WO2002037399A1

WO2002037399A1 - Sensor simulator for calibration and service of internal combustion engines

Info

Publication number: WO2002037399A1
Application number: PCT/US2001/030117
Authority: WO
Inventors: Jeffery Scott Hawkins; Kurt Joseph Couture; Ian Daniel Mckenzie
Original assignee: Detroit Diesel Corporation
Priority date: 2000-11-03
Filing date: 2001-09-25
Publication date: 2002-05-10
Also published as: AU2001296327A1

Abstract

Systems and methods for calibrating and diagnosing internal combustion engines include a sensor simulator (120) which generates a signal corresponding to a known simulated engine condition. The sensor simulator (120) includes at least one connector (122) adapted for engagement with a corresponding connector on the engine or vehicle wiring harness. The sensor simulator (120) may be connected to the engine control module (ECM 20) via the wiring harness in place of one or more actual sensors (22) to test calibration parameters or to troubleshoot engine malfunctions without uninstalling the actual sensor (22). An electric or electronic circuit within the sensor simulator (120) provides at lest one known value for use in testing calibration values and/or troubleshooting engine fault codes. Various types of sensors (22) may be simulated including position sensors, pressure sensors, temperature sensors, and level sensors.

Description

SENSOR SIMULATOR FOR CALIBRATION AND SERVICE OF INTERNAL COMBUSTION ENGINES

TECHNICAL FIELD

The present invention relates to apparatus and methods for calibrating, diagnosing, servicing, and verifying feature operation for an engine using sensor simulators.

BACKGROUND ART

Electronically controlled internal combustion engines have a wide variety of applications including passenger vehicles, marine vessels, earth-moving and construction equipment, stationary generators, and on-highway trucks, among others. Electronic engine controllers provide a wide range of flexibility in tailoring engine performance to a particular application without significant changes to engine hardware. The use of a full authority electronic controller provides a number of capabilities for enhancing engine operation, tailoring engine performance to a particular application, owner, or operator, and providing features which reduce or eliminate undesirable characteristics. As engine technology becomes increasingly more sophisticated, the number and variety of sensors used in controlling the engine has continued to climb. Typical engines may include 20 or more sensors used to provide information to the vehicle owner, operator, and service personnel and/or used to control the engine.

Sensors may be used to provide engine protection by quickly detecting adverse operating conditions which may indicate a fault or malfunction to reduce or eliminate any permanent engine damage. The engine control module (ECM) monitors the sensor inputs to detect conditions which may trigger a diagnostic code or fault which may be used by owners/operators and/or service and maintenance personnel to troubleshoot and repair the engine. Calibration variables are used to set the acceptable operating parameters for the engine and typically vary based on the engine size, type, and the application for the engine. While some calibration values are set by factory personnel, many may be modified by or at the request of the owner/operator based on the particular application. However, once a particular value is selected, it may be difficult to exercise or test the engine to determine whether a particular engine protection feature will work when needed.

In addition to monitoring sensor inputs to detect potential engine problems, the ECM typically includes logic to detect whether the sensor itself is functioning properly. However, depending upon the particular sensor, it is often difficult to determine whether the sensor is malfunctioning or whether the sensor is accurately detecting an actual adverse engine condition. As such, maintenance and service personnel must perform additional troubleshooting to diagnose the problem and repair or replace any faulty components on the engine. Troubleshooting procedures may include attempting to recreate the engine condition which triggered a fault. For example, to check engine fan operation, it is often necessary to warm the engine up to a temperature which triggers fan operation. Likewise, to test an ether start system it may be necessary to cool the engine or allow the engine to "soak" overnight when cold ambient temperatures exist. In addition, because of the complex interaction of various engine systems and sensors, multiple fault codes may be triggered in the ECM. In this situation, it is often difficult and/or time consuming for service personnel to determine which component is causing the problem. This may lead to unnecessary replacement of sensors or other components with the attendant increase of maintenance and warranty costs.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a sensor simulator for use in diagnosing engine faults, providing verification of proper function of features, and testing calibration values.

Another object of the present invention is to provide a method for troubleshooting engine diagnostic codes to reduce or eliminate unnecessary replacement of engine components.

A further object of the present invention is to provide a sensor simulator or false sensor to trigger an ECM code during troubleshooting. Another object of the present invention is to provide a sensor simulator which generates a known signal corresponding to a simulated sensed parameter.

Yet another object of the present invention is to provide sensor simulators for pressure, temperature, and level sensors for use in calibration and service of an internal combustion engine.

In carrying out the above objects, and other objects, features, and advantages of the invention a sensor simulator includes a connector adapted for engagement with a wiring harness and including at least two connector pins. The simulator includes an electric or electronic device or circuit connected between the connector pins to provide a known signal corresponding to a known sensed engine condition. In one embodiment, a resistor is connected between the pins to simulate an engine condition, such as a low coolant level, high coolant temperature, or high oil temperature. In another embodiment, a resistor network such as a voltage divider provides a signal which simulates another condition such as a low oil pressure or high crankcase pressure. Yet another embodiment includes a control to select a particular signal or value. The control may be a toggle switch, selector switch, or potentiometer, for example. Electronic or microprocessor based sensor simulators may also be provided to simulate more sophisticated sensors which may provide analog or digital signals to the ECM.

The present invention provides a number of advantages relative to prior art techniques for verifying calibration information and troubleshooting internal combustion engines. For example, the present invention may be used to test dashboard diagnostic lights and to determine whether engine protection features have been properly configured/calibrated. The present invention simplifies troubleshooting and reduces time required to diagnose faults related to engine fan controls and cold starting features such as ether start. These features may be tested and verified according to the present invention without waiting for the engine to warm up or cool down depending upon the particular feature. In addition to testing in service facilities, the present inventio may be used by the engine manufacturer during assembly and testing of the engine and/or by OEMs when building a vehicle. The above advantages, and other advantages, objects, and features of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIGURE 1 is a block diagram illustrating a prior art internal combustion engine with representative sensors for which a sensor simulator according to the present invention may be used;

FIGURE 2 illustrates a representative embodiment of a crankcase pressure sensor simulator to simulate a high pressure signal according to the present invention;

FIGURE 3 illustrates a representative embodiment of a low coolant level sensor simulator according to the present invention;

FIGURE 4 is an end view of the coolant level sensor simulator illustrated in Figure 3;

FIGURE 5 illustrates a representative embodiment of a coolant level sensor simulator with a connector adapted for engagement with a wiring harness according to the present invention;

FIGURE 6 illustrates a representative embodiment for a pump pressure sensor simulator according to the present invention;

FIGURE 7 illustrates a representative embodiment for a temperature sensor simulator with a connector adapted for engagement with a wiring harness according to the present invention;

FIGURE 8 is a circuit schematic for a two-pin sensor simulator according to one embodiment of the present invention; FIGURE 9 is a circuit schematic for a three-pin sensor simulator according to one embodiment of the present invention;

FIGURE 10 is a circuit schematic for a sensor simulator having a selectable engine condition control according to one embodiment of the present invention; and

FIGURE 11 is a flow chart illustrating a method for simulating a sensor signal according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Figure 1 provides a schematic/block diagram illustrating operation of a system or method for automatically starting an engine according to one embodiment of the present invention. System 10 includes an internal combustion engine, such as a diesel engine 12, which may be installed in a vehicle 14 depending upon the particular application. In one embodiment, vehicle 14 includes a tractor 16 and semitrailer 18. Diesel engine 12 is installed in tractor 16 and interfaces with various sensors and actuators located on engine 12, tractor 16, and semi-trailer 18 via engine and vehicle wiring harnesses as described in further detail below. In other applications, engine 12 may be used to operate industrial and construction equipment, or in stationary applications for driving generators, compressors, and/or pumps and the like.

An electronic engine control module (ECM) 20 receives signals generated by engine sensors 22 and vehicle sensors 24 and processes the signals to control engine and/or vehicle actuators such as fuel injectors 26. ECM 20 preferably includes computer-readable storage media, indicated generally by reference numeral 28 for storing data representing instructions executable by a computer to control engine 12. Computer-readable storage media 28 may also include calibration information in addition to working variables, parameters, and the like. In one embodiment, computer-readable storage media 28 include a random access memory (RAM) 30 in addition to various non-volatile memory such as read-only memory (ROM) 32, and keep-alive memory (KAM) 34. Computer-readable storage media 28 communicate with a microprocessor 38 and input/output (I/O) circuitry 36 via a standard control/address bus. As will be appreciated by one of ordinary skill in the art, computer-readable storage media 28 may include various types of physical devices for temporary and/or persistent storage of data which includes solid state, magnetic, optical, and combination devices. For example, computer readable storage media 28 may be implemented using one or more physical devices such as DRAM, PROMS, EPROMS, EEPROMS, flash memory, and the like. Depending upon the particular application, computer-readable storage media 28 may also include floppy disks, CD ROM, and the like.

In a typical application, ECM 20 processes inputs from engine sensors 22, and vehicle sensors/switches 24 by executing instructions stored in computer-readable storage media 28 to generate appropriate output signals for control of engine 12. Depending upon the particular application, the system 10 may include various types of sensors to monitor engine and vehicle operating conditions. For example, variable reluctance sensors may be used to monitor crankshaft position and/or engine speed. Variable capacitance sensors may be used to monitor various pressures such as barometric air, manifold, oil gallery, and optional pump pressures. Variable resistance sensors may be used to monitor positions such as a throttle (accelerator foot pedal) position. Magnetic pick-up sensors may be used to sense vehicle speed, accumulate trip distance, and for various other vehicle features. Likewise, thermistors may be used to monitor various temperatures such as coolant, oil, and ambient air temperatures, for example. In one embodiment of the present invention, engine sensors 22 include a timing reference sensor (TRS) 40 which provides an indication of the crankshaft position and may be used to determine engine speed. An oil pressure sensor (OPS) 42 and oil temperature sensor (OTS) 44 are used to monitor the pressure and temperature of the engine oil, respectively.

An air temperature sensor (ATS) 46 is used to provide an indication of the current intake air temperature. A turbo boost sensor (TBS) 48 is used to provide an indication of the boost pressure of a turbocharger. Coolant temperature sensor (CTS) 50 is used to provide an indication of the coolant temperature. Depending upon the particular engine configuration and application, various additional sensors may be included. For example, engines utilizing a common rail fuel system may include a corresponding fuel pressure sensor (CFPS) 52. Similarly, an intercooler coolant pressure sensor (ICPS) 54 and temperature sensor (ICTS) 56 may be provided to sense the pressure and temperature of the intercooler coolant. Engine 12 also preferably includes a fuel temperature sensor (FTS) 58 and a synchronous reference sensor (SRS) 60. SRS 60 provides an indication of a specific cylinder in the firing order for engine 12. This sensor may be used to coordinate or synchronize control of a multiple-engine configuration such as used in some stationary generator applications.

Engine 12 may also include an oil level sensor (OLS) 62 to provide various engine protection features related to a low oil level. A fuel restriction sensor (FRS) 64 may be used to monitor a fuel filter and provide a warning for preventative maintenance purposes. A fuel pressure sensor (FPS) 68 provides an indication of fuel pressure to warn of impending power loss and engine fueling. Similarly, a crankcase pressure sensor (CPS) 66 provides an indication of crankcase pressure which may be used for various engine protection features by detecting a sudden increase in crankcase pressure indicative of an engine malfunction.

System 10 preferably includes various vehicle sensors/switches 24 to monitor vehicle operating parameters and driver input used in controlling vehicle 14 and engine 12. For example, vehicle sensors/switches 24 may include a vehicle speed sensor (VSS) which provides an indication of the current vehicle speed. A coolant level sensor (CLS) 72 monitors the level of engine coolant in a vehicle radiator. Switches used to select an engine operating mode or otherwise control operation of engine 12 or vehicle 14 may include an engine braking selection switch 74 which preferably provides for low, medium, high, and off selections, cruise control switches 76, 78, and 80, a diagnostic switch 82, and various optional, digital, and/or analog switches 84. ECM 20 also receives signals associated with an accelerator or foot pedal 86, a clutch 88, and a brake 90. ECM 20 may also monitor position of a key switch 92 and a system voltage provided by a vehicle battery 94. ECM 20 may communicate with various vehicle output devices such as status indicators/lights 96, analog displays 98, digital displays 100, and various analog/digital gauges 102. In one embodiment of the present invention, ECM 20 utilizes an industry standard data link 104 to broadcast various status and/or control messages which may include engine speed, accelerator pedal position, vehicle speed, and the like. Preferably, data link 104 conforms to SAE J1939 and SAE J1587 to provide various service, diagnostic, and control information to other engine systems, subsystems, and connected devices such as display 100.

A service tool 106 may be periodically connected via data link 104 to program selected parameters stored in ECM 20 and/or receive diagnostic information from ECM 20. Likewise, a computer 108 may be connected with the appropriate software and hardware via data link 104 to transfer information to ECM 20 and receive various information relative to operation of engine 12, and/or vehicle 14.

Each of the various engine and vehicle sensors communicates with the ECM via a wiring harness. Engine and vehicle sensors typically include a connector designed for the particular sensor and application to provide reliable electrical contacts while withstanding harsh environmental conditions which allows the sensor to be replaced, if necessary. The form factor for each sensor and its corresponding connector typically varies by the type of sensor and may vary by manufacturer. According to the present invention, one or more sensor simulators are provided with a connector corresponding to the actual sensor connector which is adapted for engagement with the wiring harness. To provide a simulated known engine condition, such as a high temperature or low pressure, the corresponding sensor is disconnected from the wiring harness with the corresponding sensor simulator plugged into the wiring harness. There is no need to uninstall the engine sensor at this point, or to actually reproduce the engine condition, such as a high coolant temperature. The ECM is powered-up (the engine may be started and operated depending upon the test) using the sensor simulator so that ECM and/or other diagnostic indicators can be monitored to verify the calibration, determine if the sensor is operating correctly, etc. Figure 2 illustrates a representative embodiment of a crankcase pressure sensor simulator to simulate a high pressure signal according to the present invention. Sensor simulator 120 includes a connector 122 adapted for engagement with a wiring harness as described and illustrated with reference to Figures 5-7. A body or housing 124 contains appropriate circuitry to simulate a known or predetermined engine condition. In this embodiment, the known engine condition corresponds to a crankcase pressure which exceeds a corresponding threshold value stored in the ECM. Sensor simulator 120 may be used to simulate a high crankcase pressure condition without uninstalling the crankcase pressure sensor. Connector 122 is connected to the appropriate pigtail and the wiring harness. When the ECM is powered, a nominal 5-volt signal is applied to sensor simulator 120 which returns a voltage of about 3.5 volts which corresponds to a crankcase pressure of about 10 kPa (1.5 psig). For a typical application, the engine failure threshold is calibrated to a value of about 2.5 kPa (0.3psig) such that the simulated value exceeds the corresponding threshold stored in the ECM to activate the associated fault code.

As will be appreciated by one of ordinary skill in the art, the various representative values provided throughout the description of the invention will vary depending upon the particular application and sensor being simulated. Likewise, the sensor simulators of the preferred embodiments use a passive element such as a resistor to simulate a known engine condition. However, various other circuit elements may be provided to simulate capacitive, inductive, or any other type of sensor signal. Active elements may also be used to provide an appropriate signal to the ECM to simulate a known engine condition.

Figure 3 illustrates a representative embodiment of a low coolant level sensor simulator according to the present invention. Coolant level sensor simulator 130 includes a connector 132 adapted for engagement with a wiring harness such as the vehicle interface harness. Depending upon the particular application, one or more wiring harnesses may be used to connect the sensors and corresponding sensor simulators to the ECM. Connector 132 is preferably of the same form factor as the corresponding low coolant level sensor connector used on the engine. Sensor simulator 130 also includes a body or housing 134 which includes a circuit to provide a signal corresponding to a known engine condition. In this example, housing 134 includes a circuit to provide a low coolant level signal to the ECM. *

Figure 4 provides an end view of the coolant level sensor simulator illustrated in Figure 3. As shown in Figure 4, connector 132 may include one or more alignment or orientation pins 140 in addition to one or more conductors 142 and 144. The particular form factor for conductors 142 and 144 may vary depending upon the particular sensor and application. For example, conductors 142 and 144 may comprise pins, sockets, pads, or the like. Sensor simulators according to the present invention may also include a tab 146 to secure the simulator to the corresponding connector on the wiring harness during operation of the engine for troubleshooting and/or calibration verification purposes.

Figure 5 illustrates a representative embodiment of a coolant level sensor simulator with a connector adapted for engagement with a wiring harness according to the present invention. Sensor simulator 150 includes a connector adapted for engagement with a corresponding connector 152 on the wiring harness which is represented generally by conductors 154 and 156. The wiring harness includes one or more connectors 160 adapted for engagement with the ECM. As illustrated in Figure 5, sensor simulator 150 is coupled to the corresponding connector 152 and includes two conductors which engage with corresponding conductors in the wiring harness to simulate a known engine condition upon operation of the engine and/or powering of the ECM.

Figure 6 illustrates a representative embodiment for a pump pressure sensor simulator according to the present invention. Pump pressure sensor simulator 178 includes a body or housing 180 coupled to a connector 182 having a plurality of conductors (not shown). Connector portion 182 is adapted for engagement with a corresponding connector 184 to provide an electrical connection through conductors 186 which are coupled to the wiring harness represented by conductors 188, 190, and 192. Conductors 190 and 192 are coupled to connector 194 which is adapted for engagement with the ECM. Conductor 188 provides an available input for various applications which may utilize a pump pressure sensor. In operation, the pump pressure sensor is disconnected from connector 184 and replaced by the corresponding pump pressure sensor simulator 178. Pump pressure sensor simulator 178 provides a signal corresponding to a known engine or vehicle condition, i.e. a known pressure or pressure condition.

Referring now to Figure 7, a representative embodiment for a temperature sensor simulator with a connector adapted for engagement with a wiring harness according to the present invention is shown. Sensor simulator 200 is preferably a two-wire simulator which provides a known temperature condition or a known temperature for use in calibration, verification, and troubleshooting procedures. Simulator 200 includes a connector 202 adapted for engagement with a corresponding connector 204 on the wiring harness. Connector 204 includes two conductors 206 which are connected to the wiring harness, indicated generally by reference numeral 208. Wiring harness 208 includes corresponding conductors 210, 212 which provide an electrical connection to the ECM via a corresponding connector 214.

In operation, temperature sensor simulator 200 is connected to wiring harness 208 via connectors 202 and 206. Temperature sensor simulator 200 provides a signal representing a known engine or vehicle condition. In this example, simulator 200 may provide a signal representing a particular temperature or temperature condition for air temperature, coolant temperature, etc. The known temperature may be used to trigger a particular diagnostic or fault code in the ECM or may be used to trigger operation of various engine or vehicle accessories such as an ether start system or engine cooling fan. Various temperature sensor signal errors may be provided to test coolant temperature shutdown logic, oil temperature shutdown logic, and/or cooling fan control logic based on coolant or oil temperature, for example. As with various other sensor simulators according to the present invention, simulator 200 may also be used to test diagnostic or warning indicators or lamps.

Figure 8 is a circuit schematic for a two-pin sensor simulator according to one embodiment of the present invention. In the embodiment of Figure 8, sensor simulator 220 includes conductors 222 and 224 which are coupled via a passive circuit element 226, such as a resistor. Passive circuit element 226 is used to provide a signal indicative of a known engine or vehicle condition. In one embodiment, passive circuit element 226 provides a signal corresponding to a temperature of 250 °F or 121 °C by providing a nominal resistance of about 100 ohms. The signal provided by the ECM is a nominal 5-volt signal. A passive circuit element 226, such as a resistor, may be implemented using conventional discrete components, a solid state device, surface mount device, or the like. Likewise, rather than providing a simulator which produces a single, specific temperature, multiple selectable resistors may be provided to switch between corresponding specific temperatures or a variable resistor/potentiometer may be used to vary the temperature signal throughout a selected temperature range.

Figure 9 is a circuit schematic for a three-pin sensor simulator according to one embodiment of the present invention. Sensor simulator 230 includes at least three conductors 232, 234, and 236 coupled by a voltage divider circuit comprising resistors 238 and 240. Sensor simulator 230 is preferably used to produce a signal or signals which simulate a specific pressure. When connected to the ECM via a wiring harness, the ECM provides a voltage across conductors 232 and 236. The resulting voltage between conductors 232 and 234, or alternatively between 234 and 236, is used to simulate a known engine condition or specific pressure. For example, a specific pressure may correspond to a low pressure signal relative to corresponding calibration variables stored in the ECM. Similar to the temperature sensor simulator described with reference to Figure 8, pressure simulators according to the present invention may also include selectable voltage divider circuits which provide corresponding selectable specific pressures. Likewise, a variable resistence device, such as a potentiometer, may be used to vary the indicated pressure throughout a selected pressure range.

Figure 10 is a circuit schematic for a sensor simulator having a selectable engine condition control according to one embodiment of the present invention. Sensor simulator 250 includes conductors 252, 254, and 256 with selectable voltage divider circuits connected therebetween. One of the plurality of circuits or circuit elements is selected using a corresponding selector 258. In this example, selector 258 which may be a toggle switch, connects either one of resistors 260, 262 in series with resistor 264 to form a voltage divider network or circuit among conductors 252, 254, and 256. Depending upon the particular application, selector 258 may be used to select a particular known engine or vehicle condition from numerous available conditions with corresponding circuits or circuit elements in a similar fashion.

In operation, sensor simulator 250 is connected to the engine or vehicle wiring harness in place of a corresponding sensor. One of the available known engine conditions is selected via selector 258. The ECM is then powered-up and/or the engine is operated to execute the corresponding control logic with the sensor simulator 250 providing a simulated engine condition to trigger vehicle accessories and/or engine/vehicle diagnostic codes.

Figure 11 is a flowchart illustrating a method for simulating a sensor signal according to the present invention. Block 280 of Figure 11 represents disconnecting the engine sensor from the corresponding wiring harness. Depending upon the particular application, the ECM may include one or more wiring harnesses to connect the various sensors and actuators to the ECM. Step 280 is preferably performed without actually uninstalling or removing the engine/vehicle sensor which is to be simulated. A corresponding sensor simulator is connected to the wiring harness in place of the actual sensor as represented by block 282. For simulators which include multiple available engine conditions, one of the conditions is selected as represented by block 284. The selection may be made with a corresponding selector switch or dial on the sensor simulator as described above.

After the sensor simulator has been connected to the wiring harness (and an engine condition has been selected, if applicable), the ECM is powered-up and/or the engine is started with the sensor simulator in place as represented by block 286. As will be appreciated by one of ordinary skill in the art, depending upon the particular sensor simulator, the calibrations may be verified and/or diagnostic codes may be set without actually running the engine. Other codes or calibrations can be verified only upon actual operation of the engine.

The simulated engine condition provided by the sensor simulator is used to generate and analyze results as represented by block 288. Again, depending upon the particular application and sensor simulator, block 288 may be performed by monitoring diagnostic indicators 290, checking ECM diagnostic codes 292, or monitoring operation of an engine accessory or component 294. For example, diagnostic indicators represented by block 290 may include a check engine light, stop engine light, or various other alarms or lights. ECM codes include various diagnostic and/or fault codes generated by the ECM which may be monitored by a service tool as illustrated in Figure 1. Alternatively, engine codes may be communicated by flashing lights, or a dashboard display 100 (Figure 1). Visual inspections of various engine/vehicle components may include monitoring operation of a cooling fan, for example.

As such, the present invention provides a method and apparatus for use in calibrating and servicing an internal combustion engine which provide a number of advantages relative to the prior art. The sensor simulators can be quickly and easily connected to the engine/vehicle harness to generate a signal corresponding to a known simulated engine condition to reduce time required for troubleshooting and verification of engine protection systems and the like.

While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. A sensor simulator for an internal combustion engine including an engine control module (ECM) in communication with a plurality of sensors via a wiring harness, the simulator comprising: a connector adapted for engagement with the wiring harness; and a circuit coupled to the connector for providing a signal corresponding to a known simulated engine or vehicle condition.

2. The sensor simulator of claim 1 wherein the circuit comprises at least one resistor.

3. The sensor simulator of claim 2 wherein the connector includes at least three conductors for engagement with corresponding conductors in the wiring harness and wherein the at least one resistor includes a plurality of resistors arranged as a voltage divider between the at least three conductors.

4. The sensor simulator of claim 3 wherein the circuit generates a signal corresponding to an abnormal crankcase pressure as determined by at least one corresponding crankcase pressure calibration value stored in the ECM.

5. The sensor simulator of claim 3 wherein the circuit generates a signal corresponding to an abnormal oil pressure as determined by at least one corresponding oil pressure calibration value stored in the ECM.

6. The sensor simulator of claim 2 wherein the circuit generates a signal corresponding to a known coolant temperature as determined by a corresponding coolant temperature calibration value stored in the ECM.

7. The sensor simulator of claim 2 wherein the circuit generates a signal corresponding to a known oil temperature as determined by a corresponding oil temperature calibration value stored in the ECM.

8. The sensor simulator of claim 2 wherein the circuit generates a signal indicating a low fluid level.

9. The sensor simulator of claim 2 wherein the circuit generates a signal indicating a restriction in an engine fluid circuit.

10. The sensor simulator of claim 9 wherein the circuit generates a signal indicated an airflow restriction.

11. The sensor simulator of claim 1 wherein the circuit comprises at least one selector switch for selecting one of a plurality of known simulated engine or vehicle conditions.

12. A sensor simulator for use with an internal combustion engine having a plurality of sensors connected via respective connectors to at least one wiring harness which is connected to a an engine control module (ECM), the sensor simulator comprising: a housing: a connector coupled to the housing and adapted for engagement with at least one of the connectors on the at least one wiring harness, the connector including at least two conductors adapted for engagement with corresponding conductors of the wiring harness; a circuit disposed within the housing and including at least one passive circuit element connected between the at least two conductors, the passive circuit element providing a sensor signal corresponding to a known engine condition when connected to the wiring harness during operation of the engine.

13. The sensor simulator of claim 12 wherein the connector includes at least three conductors and wherein the circuit includes at least two resistors connected to provide a voltage divider circuit via three of the conductors.

14. The sensor simulator of claim 12 wherein the passive circuit element comprises a variable resistor.

15. The sensor simulator of claim 12 wherein the passive circuit element comprises a plurality of resistors, the simulator further comprising: a selector switch positioned on the housing and connected to the plurality of resistors to select one of the plurality of resistors to simulate one of a plurality of known engine conditions.

16. A method for operating an internal combustion engine having an engine control module (ECM) connected via at least one wiring harness to a plurality of engine sensors, the method comprising: disconnecting at least one of the plurality of engine sensors from the wiring harness without removing the sensor from the engine; connecting a sensor simulator to the wiring harness in place of the engine sensor, the sensor simulator providing a signal corresponding to a known engine operating condition; and running the engine while the sensor simulator is connected to the wiring harness.

17. The method of claim 16 wherein the sensor simulator provides a signal corresponding to a high temperature relative to a corresponding temperature calibration stored in the ECM to trigger operation of at least one engine cooling fan.

18. The method of claim 16 wherein the sensor simulator provides a signal corresponding to a low coolant level.

19. The method of claim 16 wherein the sensor simulator provides a signal corresponding to a restriction in an engine fluid flow.

20. The method of claim 16 further comprising: selecting one known engine operating condition from a plurality of known engine operating conditions using a selector switch on the sensor simulator.