Engine Controls Self-Diagnostics - 6.6L Diesel: Overview Chevrolet Silverado 2500

MODEL IDENTIFICATION

Vehicle model is identified by the fifth character of Vehicle Identification Number (VIN). VIN is stamped on metal pad on top of left end of instrument panel, near windshield. See MODEL IDENTIFICATION table.

MODEL IDENTIFICATION

Description

The Diagnostic System Check is an organized approach to identifying a condition that is created by a malfunction in the powertrain control system. The Diagnostic System Check must be the starting point for any driveability concern. The Diagnostic System Check directs the service technician to the next logical step in order to diagnose the concern. Understanding and correctly using the diagnostic table reduces diagnostic time, and prevents the replacement of good parts.

Test Description

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 Lack of communication may be caused by a partial or a total malfunction of the Class 2 serial data circuit. The specified procedure determines the particular condition.
2. 5 This step stores the Engine Control Module (ECM) Diagnostic Trouble Code (DTC) information into the scan tool's memory. After you complete the diagnostic procedure, review the captured information in order to catch the next DTC if the control module stores multiple DTCs. Review the Freeze Frame data and the Failure Records data. Use this information in order to determine how frequently and how recently the DTC set. This information may help diagnose an intermittent condition. Information about the operating conditions at the time that the DTC set may also help diagnose an intermittent condition. Capturing the stored information saves the data that the ECM loses during the following conditions: When a diagnostic procedures instructs you to clear the DTCs. When a diagnostic procedure instructs you to disconnect the ECM connectors. When a diagnostic procedure instructs you to replace the ECM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article.
3. 6 The presence of DTCs which begin with "U", indicate that some other module is not communicating. Following the specified procedure will gather all the available information before you perform the tests. DTC U1800, U2104, and U2106 are CAN communications codes, and are not part of the class 2 Data Link system.
4. 9 If there are other modules with DTCs set, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-138411-S02438938112002041200000) . The DTC list directs you to the appropriate diagnostic procedure. If the control module stores multiple powertrain DTCs, diagnose the DTCs in the following order: Component level DTCs, such as sensor DTCs, solenoid DTCs, and relay DTCs. Diagnose the multiple DTCs within this category in numerical order. Begin with the lowest numbered DTC, unless the diagnostic table directs you otherwise. System level DTCs, for example, misfire DTCs, fuel trim DTCs, and catalyst DTCs.

Several states require that a vehicle pass on-board diagnostic (OBD) system tests and the I/M emission inspection in order to renew license plates. This is accomplished by viewing the I/M System Status display on a scan tool. Using a scan tool, the technician can observe the I/M System Status in order to verify that the vehicle meets the criteria that complies with the local area requirements.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 1 Any DTCs set, even those that are not listed in the INSPECTION/MAINTENANCE SYSTEM DTCS table, may prevent the required DTCs from running. If there is any question as to whether a set DTC is disabling the required I/M diagnostic, review the Conditions for Running in the diagnostic procedures for the DTC required by the I/M diagnostic. A list of disabling DTCs, if applicable, is contained in the supporting text for that DTC.
2. 2 Anytime a control module is reprogrammed or the diagnostic trouble codes are cleared as part of a repair procedure, all the I/M System Status indicators will reset to NO.
3. 3 Use discretion when determining whether the entire system set procedure needs to be performed. For example, if the only tests that have not run are those that require the engine to be at operating temperature, then only those individual tests need to be run. There is no need to allow the engine to completely cool in order to run these tests.

The purpose of the I/M Complete System Set Procedure is to satisfy the enable criteria necessary to execute all of the I/M readiness diagnostics, and complete the trips for those particular diagnostics. When all diagnostic tests are complete, the I/M System Status indicators are set to YES. Perform this test when more than one or all of the I/M System Status indicators are set to NO.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 1 Make sure that you perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2 This step initiates the Component Monitoring Tests.
3. 3 The cruise portion of the step runs a portion of the Component Monitoring Tests and to prepare for the remaining tests.
4. 4 The acceleration portion of the step completes the Component Monitoring Tests and the idle portion completes the Misfire Monitoring diagnostic tests.
5. 5 Perform the individual system test for any of the systems that do not update to YES.
6. 6 The I/M System Status only reports on whether or not a diagnostic test has run, not the outcome of the test. If any emission related DTC sets after the tests are complete, the DTC will require diagnosis.

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostic tests for the Component Monitoring System. The test may be used to set the I/M System Status to YES. Ensure that the vehicle meets the requirements in Conditions for Running before performing this test. Failure to meet the necessary requirements may produce inaccurate test results.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 1 Ensure that you perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 3 This step identifies a first failure of a type "B" DTC. A DTC only appears on the I/M System Status display when the DTC becomes a MIL illuminating DTC. This occurs on the second failure of a type "B" DTC. A first failure of a type "B" DTC will not allow the I/M System Status to update to YES. See «DIAGNOSTIC AIDS»(ref-138411-S26735528532002041200000) .
3. 4 This step helps identify any unique or any unusual criteria required to run the diagnostic test in the event the universal set procedure does not. This information is located in the service information under Conditions for Running DTC.
4. 5 The I/M System Status only reports on whether or not a diagnostic has run, not the outcome of the test. If any Emission Related DTC sets after the tests are complete, the DTC will require diagnosis.

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostic tests for the Misfire Monitoring System. The test may be used to set the I/M System Status to YES. Make sure that the vehicle meets the requirements in Conditions for Running before performing this test. Failure to meet the necessary requirements may produce inaccurate test results.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 1 Ensure that you perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 3 This step is to identify a first failure of a type "B" DTC. A DTC only appears on the I/M System Status display when the DTC becomes a MIL illuminating DTC. This occurs on the second failure of a type "B" DTC. A first failure of a type "B" DTC will not allow the I/M System Status to update to YES. See «DIAGNOSTIC AIDS»(ref-138411-S12804033532002041200000) .
3. 4 This step is to help identify any unique or unusual criteria required to run the diagnostic test in the event the universal set procedure does not. This information is located in Conditions for Running DTC.
4. 5 The I/M System Status only reports on whether or not a diagnostic has run, not what the outcome of the test was. If any Emission Related DTC sets after the tests are complete, the DTC will require diagnosis.

The battery positive voltage is supplied directly to the Malfunction Indicator Lamp (MIL). The Engine Control Module (ECM) turns the MIL ON by grounding the MIL control circuit. There should be a steady MIL with the ignition ON and the engine OFF.

MIL Operation

The MIL is located on the Instrument Panel (IP).

MIL Function

1. The MIL informs the driver that a malfunction has occurred and the vehicle should be taken in for service as soon as possible.
2. The MIL illuminates during a bulb test and a system test.
3. A DTC will be stored if a MIL is requested by the diagnostic.

MIL Illumination

1. The MIL will illuminate with ignition ON, and the engine not running.
2. The MIL will turn OFF when the engine is started.
3. The MIL will remain ON if the self-diagnostic system has detected a malfunction.
4. The MIL may turn OFF if the malfunction is not present.
5. If the MIL is illuminated and then the engine stalls, the MIL will remain illuminated so long as the ignition is ON.
6. If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition is cycled OFF, then ON.

The numbers below refer to the step numbers n the diagnostic procedures.

1. 3 This step determines if the condition is with the MIL control circuit or the ECM.
2. 4 This step determines if a voltage is constantly being applied to the control circuit.

The battery positive voltage is supplied directly to the Malfunction Indicator Lamp (MIL). The Engine Control Module (ECM) turns the MIL ON by grounding the MIL control circuit.

The MIL is located on the Instrument Panel (IP).

MIL Function

1. The MIL informs the driver that a malfunction has occurred. The vehicle should be serviced as soon as possible.
2. The MIL illuminates during a bulb test, and during a system test.
3. A DTC will be stored if the diagnostic test requests a MIL.

MIL Illumination

1. The MIL will illuminate with ignition switch ON, and with the engine not running.
2. The MIL will turn OFF when the you start the engine.
3. The MIL will remain ON if the self-diagnostic system detects a malfunction.
4. The MIL may turn OFF if the malfunction is not present.
5. If the MIL is illuminated and then the engine stalls, the MIL will remain illuminated if the ignition switch is ON.
6. If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition switch is cycled OFF, and cycled ON again.

The number below refers to the step number in the diagnostic procedures.

1. 3 The step determines if the condition is with the MIL control circuit or the ECM.

The Engine Control Module (ECM) monitors Fuel Rail Pressure (FRP) using the FRP sensor. If the sensor indicates a pressure less than the commanded rail pressure plus a possible transitional overshoot, the ECM will set Diagnostic Trouble Code (DTC) P0087 for fuel rail pressure too low.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 If the engine starts, there is adequate fuel pressure. A restriction in a fuel line or a sensor fault exists.
2. 7 If the FRP is above 23 MPa, there is adequate pressure at this time.
3. 8 An open in the FRP sensor circuit will cause the ECM to show the maximum reading of over 175 MPa.
4. 9 If the engine starts, the problem is a faulty fuel rail pressure sensor.

The Engine Control Module (ECM) monitors Fuel Rail Pressure (FRP) using the FRP sensor. If the sensor indicates a pressure more than the commanded rail pressure plus a possible transitional overshoot, The ECM will set Diagnostic Trouble Code (DTC) P0088 for fuel rail pressure too high.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 DTC P0090 is a current flow problem in the FRP regulator circuit. This incorrect current draw could lead to incorrect fuel pressure. This hardware problem should be diagnosed before the performance DTC is checked. See «DTC P0090: FUEL RAIL PRESSURE SENSOR CURRENT OUT OF RANGE»(ref-138411-S20369296622002041200000) .

The Engine Control Module (ECM) uses commanded fuel pump flow to determine a desired Fuel Rail Pressure (FRP). The actual fuel pressure is monitored using the FRP sensor. If the FRP sensor indicates a pressure more than 20 MPa greater than desired, DTC P0089 will set.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 DTC P0090 is a current flow problem in the FRP regulator circuit. This incorrect current draw could lead to incorrect fuel pressure. This hardware problem should be diagnosed before the performance DTC is checked.
2. 3 DTC P1093 indicates a major leak in the fuel system. All fuel leaks and electrical circuit faults must be diagnosed before the performance DTC is checked.
3. 5 A restriction in the fuel return system may cause this DTC to set. A plugged return line will result in a leak.

The Engine Control Module (ECM) supplies power and ground to the fuel rail pressure (FRP) regulator. The ECM monitors current on the circuits to detect a failure. If the current is outside of the expected range, DTC P0090 will set.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 6 This step tests for battery voltage through the ECM to the FRP regulator.
2. 7 This step tests for an open control circuit between the ECM and the FRP regulator.
3. 8 This excessive current code can be set by voltage being applied between the ECM and the FRP regulator on the FRP control circuit.

The Mass Air Flow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The Engine Control Module (ECM) uses the MAF sensor voltage signal in order to provide the correct fuel delivery for a reduction in emissions. The ECM uses the MAF sensor signal in order to control fuel delivery until a calibrated amount of engine air flow is attained. The MAF sensor has an ignition 1 voltage circuit, a signal circuit and a low reference circuit. The MAF sensor produces an output voltage based on inlet air flow through the air induction system. This output voltage will display on the scan tool as a grams per second (g/s) value. The ECM will calculate a predicted MAF value. The ECM compares the actual MAF sensor voltage signal to the predicted MAF value. This comparison will determine if the signal is stuck, or is too low or too high for a given operating condition. DTC P0101 will set if the actual MAF sensor voltage signal is not within a predetermined range of the calculated MAF value.

The Mass Air Flow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The Engine Control Module (ECM) uses the MAF sensor voltage signal in order to provide the correct fuel delivery for a reduction in emissions. The ECM uses the MAF sensor signal in order to control fuel delivery until a calibrated amount of engine air flow is attained. The MAF sensor has an ignition 1 voltage circuit, a signal circuit and a low reference circuit. The MAF sensor produces an output voltage based on inlet air flow through the air induction system. This output voltage will display on the scan tool as a grams per second (g/s) value. DTC P0102 will set if the actual MAF sensor voltage signal is less than the possible range of a normally operating sensor.

The number below refers to the step numbers in the diagnostic procedures.

1. 11 A short to another ECM-controlled circuit may not be present when the ECM is disconnected as part of the previous test. A short across two ECM circuits can cause this DTC to set.

The Mass Air Flow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The Engine Control Module (ECM) uses the MAF sensor voltage signal in order to provide the correct fuel delivery for a reduction in emissions. The ECM uses the MAF sensor signal in order to control fuel delivery until a calibrated amount of engine air flow is attained. The MAF sensor has an ignition 1 voltage circuit, a signal circuit and a low reference circuit. The MAF sensor produces an output voltage based on inlet air flow through the air induction system. This output voltage will display on the scan tool as a grams per second (g/s) value. DTC P0103 will set if the actual MAF sensor voltage signal is more than the possible range of a normally operating sensor.

The Barometric (BARO) pressure sensor responds to changes in altitude and atmospheric conditions. This gives the Engine Control Module (ECM) an indication of barometric pressure. The ECM uses this information to calculate fuel delivery. The BARO sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The ECM supplies 5 volts to the BARO sensor on the 5-volt reference 2 circuit, and provides a ground on a low reference circuit. The BARO sensor provides a signal to the ECM on a signal circuit relative to the pressure changes. The ECM compares the BARO sensor to the Exhaust Gas Recirculation (EGR) vacuum sensor in order to monitor the BARO sensor operation. This DTC will set if the difference between the 2 sensors is more than a predetermined amount.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 This step tests the BARO sensors ability to correctly indicate barometric pressure. The value shown for the BARO sensor varies with altitude.
2. 4 The EGR system will activate at idle when the coolant temperature is more than 140°F (60°C). The EGR system must be disabled for this step.
3. 5 This step tests for a sensor stuck in range.

The Barometric (BARO) pressure sensor responds to changes in altitude and atmospheric conditions. This gives the Engine Control Module (ECM) an indication of barometric pressure. The ECM uses this information to calculate fuel delivery. The BARO sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The ECM supplies 5 volts to the BARO sensor on the 5-volt reference 2 circuit, and provides a ground on a low reference circuit. The BARO sensor provides a signal to the ECM on a signal circuit relative to the pressure changes. The ECM compares the BARO sensor to the boost sensor in order to monitor the BARO sensor operation. This DTC will set if the difference between the two sensors is more than a predetermined amount.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 This step tests the BARO sensors ability to correctly indicate barometric pressure. The value shown for the BARO sensor varies with altitude.
2. 4 This step tests for a sensor stuck in range.

The Barometric (BARO) pressure sensor responds to changes in altitude and atmospheric conditions. This gives the Engine Control Module (ECM) an indication of barometric pressure. The ECM uses this information to calculate fuel delivery. The BARO sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The ECM supplies 5 volts to the BARO sensor on the 5-volt reference 2 circuit, and provides a ground on a low reference circuit. The BARO sensor provides a signal to the ECM on a signal circuit relative to the pressure changes. The ECM monitors the BARO sensor signal for voltage outside of the normal range. If the ECM detects a BARO sensor signal voltage that is excessively low, this DTC will set.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 The BARO sensor 5-volt reference circuit is shared with other sensors. If DTC P1639 is set, this indicates that the 5-volt reference circuit is shorted to ground and should be diagnosed first. The short may be on another sensor 5-volt reference circuit.
2. 4 Operate the vehicle within the same conditions as when the DTC failed. If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data can aid in locating an intermittent condition.

The Barometric (BARO) pressure sensor responds to changes in altitude and atmospheric conditions. This gives the Engine Control Module (ECM) an indication of barometric pressure. The ECM uses this information to calculate fuel delivery. The BARO sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The ECM supplies 5 volts to the BARO sensor on the 5-volt reference 2 circuit, and provides a ground on a low reference circuit. The BARO sensor provides a signal to the ECM on a signal circuit relative to the pressure changes. The ECM monitors the BARO sensor signal for voltage outside of the normal range. If the ECM detects a BARO sensor signal voltage that is excessively low, this DTC will set.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 The BARO sensor 5-volt reference circuit is shared with other sensors. If DTC P1639 is set, this indicates that the 5-volt reference circuit is shorted to ground and should be diagnosed first. The short may be on another sensor 5-volt reference circuit.
2. 4 Operate the vehicle within the same conditions as when the DTC failed. If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data can aid in locating an intermittent condition.

The Barometric (BARO) pressure sensor responds to changes in altitude and atmospheric conditions. This gives the Engine Control Module (ECM) an indication of barometric pressure. The ECM uses this information to calculate fuel delivery. The BARO sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The ECM supplies 5 volts to the BARO sensor on the 5-volt reference 2 circuit, and provides a ground on a low reference circuit. The BARO sensor provides a signal to the ECM on a signal circuit relative to the pressure changes. The ECM monitors the BARO sensor signal for voltage outside of the normal range. If the ECM detects a BARO sensor signal voltage that is excessively high, this DTC will set.

The number below refers to the step number in the diagnostic procedures.

1. 4 A short to voltage on the 5-volt reference circuit will cause DTC P1639 to set.
2. 7 This step tests the signal circuit of the BARO sensor for a short to voltage. The short may backfeed through the sensor to the 5-volt reference circuit causing the DTC P1639 to set.
3. 8 This step tests the signal circuit of the boost sensor for a short to voltage. The short may backfeed through the sensor to the 5-volt reference circuit causing the DTC P1639 to set.
4. 9 This step tests the signal circuit of the EGR vacuum sensor for a short to voltage. The short may backfeed through the sensor to the 5-volt reference circuit causing the DTC P1639 to set.

The Barometric (BARO) pressure sensor responds to changes in altitude and atmospheric conditions. This gives the Engine Control Module (ECM) an indication of barometric pressure. The ECM uses this information to calculate fuel delivery. The BARO sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The ECM supplies 5 volts to the BARO sensor on the 5-volt reference 2 circuit, and provides a ground on a low reference circuit. The BARO sensor provides a signal to the ECM on a signal circuit relative to the pressure changes. The ECM monitors the BARO sensor signal for voltage outside of the normal range. If the ECM detects a BARO sensor signal voltage that is excessively high, this DTC will set.

1. 4 A short to voltage on the 5-volt reference circuit will cause DTC P1639 to set.
2. 7 This step tests the signal circuit of the BARO sensor for a short to voltage. The short may backfeed through the sensor to the 5- volt reference circuit causing the DTC P1639 to set.
3. 8 This step tests the signal circuit of the boost sensor for a short to voltage. The short may backfeed through the sensor to the 5-volt reference circuit causing the DTC P1639 to set.

The Intake Air Temperature (IAT) sensor is a variable resistor, sometimes called a thermistor. The IAT sensor measures the temperature of the air entering the engine. The Engine Control Module (ECM) supplies 5 volts to the IAT signal circuit. When the IAT sensor is cold, the sensor resistance is high. When the air temperature increases, the sensor resistance lowers. With high sensor resistance, the ECM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the ECM detects a lower voltage on the IAT signal circuit. If the ECM detects an excessively low IAT signal voltage, indicating a high temperature, DTC P0112 sets.

The Intake Air Temperature (IAT) sensor is a variable resistor, sometimes called a thermistor. The IAT sensor measures the temperature of the air entering the engine. The Engine Control Module (ECM) supplies 5 volts to the IAT signal circuit. When the IAT sensor is cold, the sensor resistance is high. When the air temperature increases, the sensor resistance lowers. With high sensor resistance, the ECM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the ECM detects a lower voltage on the IAT signal circuit. If the ECM detects an excessively high IAT signal voltage, indicating a low temperature, DTC P0113 sets.

The number below refer to the step number in the diagnostic procedures.

1. 6 This step tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.

The Engine Coolant Temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The Engine Control Module (ECM) supplies 5 volts to the signal circuit. When coolant temperatures are low, resistance is high. When coolant temperatures are high the resistance is low. The ECM uses this input for engine controls and enabling criteria for diagnostics. The ECM will record the amount of time the engine is OFF. At restart the ECM will compare the temperature difference between the ECT and Intake Air Temperature (IAT). If the temperature difference is not within the calculated amount, after the predetermined soak time, DTC P0116 sets. Before failing this test, the ECM will check for the presence of a block heater.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 This step tests for excessive resistance in the ECT sensor circuit.
2. 4 This step tests for excessive resistance in the IAT sensor circuit.
3. 5 This step tests for a skewed sensor through the range of temperatures affecting this DTC.

The Engine Coolant Temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures the temperature of the engine coolant. The Engine Control Module (ECM) supplies 5 volts to the ECT signal circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance lowers. With high sensor resistance, the ECM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the ECM detects a lower voltage on the ECT signal circuit. If the ECM detects an excessively low ECT signal voltage, which is a high temperature indication, DTC P0117 sets.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 If DTC P0117 can only be repeated by duplicating the Failure Records, refer to Temperature vs Resistance table. The table may be used to test the ECT sensor at various temperatures in order to evaluate the possibility of a shifted sensor that may be shorted above or below a certain temperature. If the ECT sensor appears to be okay, the malfunction is intermittent: see «DIAGNOSTIC AIDS»(ref-138411-S30207927902002041200000) .
2. 5 When testing ECT signal circuit for a short to ground, you may need to inspect for continuity between all other ECM circuits.

The Engine Coolant Temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures the temperature of the engine coolant. The Engine Control Module (ECM) supplies 5 volts to the ECT signal circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance lowers. With high sensor resistance, the ECM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the ECM detects a lower voltage on the ECT signal circuit. If the ECM detects an excessively high ECT signal voltage, which is a low temperature indication, DTC P0118 sets.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 If DTC P0118 can only be repeated by duplicating the Failure Records, refer to the Temperature vs Resistance table. The table may be used to test the ECT sensor at various temperatures to evaluate the possibility of a shifted sensor that may be shorted above or below a certain temperature. If the ECT sensor appears to be okay, the malfunction is intermittent. See «DIAGNOSTIC AIDS»(ref-138411-S13679526022002041200000) .
2. 4 This step tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.
3. 10 The ECM in this vehicle use an Electrically Erasable Programmable Read-Only Memory (EEPROM). If the ECM is replaced, the new ECM must be programmed.

An Engine Coolant Temperature (ECT) sensor monitors the temperature of the coolant. The fuel burned since start up is used to determine if the engine has been driven within conditions that would allow the engine coolant to heat up normally to the thermostat regulating temperature. If the coolant temperature does not increase normally, or does not reach regulating temperature of the thermostat, diagnostics that use engine coolant temperature as enabling criteria, may not run when expected. If engine coolant fails to reach a preset target temperature before the calculated amount of fuel is burned, DTC P0128 will set. This Diagnostic Trouble Code (DTC) will only run once per ignition cycle until a Pass, Fail or Disable condition exists.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 This step tests for excessive resistance in the ECT circuit.
2. 4 This step tests for a skewed sensor through the range of temperatures affecting this DTC.

The Fuel Rail Temperature (FRT) sensor is a thermistor type sensor. The Engine Control Module (ECM) supplies 5 volts and a ground circuit to the sensor. When the ECM detects a FT above a pre-determined value, a type C code, no Malfunction Indicator Lamp (MIL) sets. A fuel cooler located in front of the fuel tank is used to help keep the fuel temperature at an acceptable limit.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 This step checks for a problem in the fuel cooler that could cause the FRT to increase above the pre-determined specification due to a lack of cooler efficiency.
2. 5 This step checks for a voltage above or below the 5 volts supplied by the ECM.

The fuel temperature sensor is a thermistor. The Engine Control Module (ECM) supplies the fuel temperature sensor a reference voltage of 5 volts on the signal circuit and also provides a low reference circuit to the sensor. When the fuel temperature sensor is cold, the resistance is high. The fuel temperature sensor signal voltage remains near the supplied voltage cold and decreases the signal voltage as the sensor warms. The control module monitors the fuel temperature sensor signal circuit in order to calculate the temperature of the fuel entering the engine.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 This step determines if the IAT sensor reading is reading within a normal range. If the reading is outside of the specification, the IAT sensor may have a fault in the sensor or circuit.
2. 3 This step determines if the fault is present at the time of diagnosis.
3. 11 Reprogram the replacement ECM. See «ENGINE CONTROL MODULE»(ref-138411-S14665279672002041200000) under PROGRAMMING.

The Fuel Rail Temperature (FRT) sensor is a thermistor. The Engine Control Module (ECM) supplies the FRT sensor a reference voltage of 5 volts on the signal circuit and also provides a low reference circuit to the sensor. When the FRT sensor is cold, the resistance is high. The FRT sensor signal voltage remains near the supplied voltage cold and decreases the signal voltage as the sensor warms. The control module monitors the FRT sensor signal circuit in order to calculate the temperature of the fuel entering the engine. If the ECM detects an excessively low FRT signal voltage, a high temperature indication, this DTC will set.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 If DTC P0182 can only be repeated by duplicating the Failure Records, refer to Temperature vs Resistance table. The table may be used to test the FRT sensor at various temperatures in order to evaluate the possibility of a shifted sensor that may be shorted above or below a certain temperature. If this is the case, replace the FRT sensor. If the FRT sensor appears to be okay, the malfunction is intermittent: see «DIAGNOSTIC AIDS»(ref-138411-S29962531722002041600000) .
2. 5 When testing FRT sensor signal circuit for a short to ground, you may need to inspect for continuity between all other PCM circuits.

The Fuel Rail Temperature (FRT) sensor is a thermistor. The Engine Control Module (ECM) supplies the FRT sensor a reference voltage of 5 volts on the signal circuit and also provides a ground circuit to the sensor. When the FRT sensor is cold, the resistance is high. The FRT sensor signal voltage remains near the supplied voltage cold and decreases the signal voltage as the sensor warms. The control module monitors the FRT sensor signal circuit in order to calculate the temperature of the fuel entering the engine. If the ECM detects an excessively high FRT voltage, a low temperature indication, this DTC will set.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 If DTC P0183 can only be repeated by duplicating the Failure Records, refer to the Temperature vs Resistance table. The table may be used to test the FT sensor at various temperatures to evaluate the possibility of a shifted sensor that may be shorted above or below a certain temperature. If this is the case, replace the FT sensor. If the FT sensor appears to be okay, the malfunction is intermittent. See «DIAGNOSTIC AIDS»(ref-138411-S21689263332002041600000) .
2. 4 Tests for the proper operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.
3. 10 The ECM in this vehicle uses an Electrically Erasable Programmable Read-Only Memory (EEPROM). If the PCM is replaced, the new ECM must be programmed.

The Engine Control Module (ECM) monitors the fuel rail pressure via a Fuel Rail Pressure (FRP) sensor. When the fuel rail pressure is high the signal voltage is high. When the fuel rail pressure is low the signal voltage is low. If the fuel rail pressure is not above the lower limit for the sensor, DTC P0192 will set.

The numbers below refer to the step numbers on the diagnostic procedures.

1. 3 This step tests for the proper operation of the circuit in the low voltage range.
2. 4 This step tests for the proper operation of the circuit in the high voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to ground.

The Engine Control Module (ECM) monitors the fuel rail pressure via a Fuel Rail Pressure (FRP) sensor. When the fuel rail pressure is high the signal voltage is high. When the fuel rail pressure is low the signal voltage is low. If the fuel rail pressure is above the upper limit for the sensor, DTC P0193 will set.

The Fuel Injection Control Module (FICM) supplies high voltage to each fuel injector on the ignition voltage circuits. The FICM energizes each fuel injector by grounding the command circuit between the FICM and the fuel injector. The FICM monitors the status of the ignition voltage circuits and the fuel injector command circuits. When a fuel injector circuit condition is detected by the FICM, all of the fuel injectors on the affected ignition voltage circuit will be disabled. If a circuit condition is detected on a fuel injector circuit for cylinders 1, 4, 6, or 7, DTCs P0201, P0204, P0206, P0207 will set, along with DTC P1261. If a circuit condition is detected on a fuel injector circuit for cylinders 2, 3, 5, or 8, DTCs P0202, P0203, P0205, P0208 will set, along with DTC P1262.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 This step verifies that the condition is not intermittent.
2. 4 This step determines which set of fuel injectors the circuit condition is affecting. If DTC P1261 is set, then a condition exists on cylinders 1, 4, 6, or 7. If DTC P1262 is set, then a condition exists on cylinders 2, 3, 5, or 8.
3. 5 This step tests if a ground is constantly being applied to the fuel injectors.
4. 6 This step isolates which circuit is causing the condition. If the test lamp turns OFF when a multi-way connector is disconnected, test the affected circuits for a short to ground.
5. 7 This step tests for an open circuit. If the Digital Multimeter (DMM) displays OL on all of the fuel injector circuits, the ignition voltage circuit is open.
6. 8 This step tests for an open circuit. If the DMM displays OL on one of the fuel injector circuits, the fuel injector command circuit is open.
7. 9 This step tests for excessive resistance in a fuel injector circuit.
8. 10 This step is testing for a short between the ignition feed circuit, and the fuel injector command circuit. If the resistance of the circuits is less than 0.3 ohms, test for a short between the circuits. If a short cannot be found, the fuel injector may be the cause of the condition. The normal fuel injector resistance is between 0.3-0.4 ohms.
9. 11 This step tests for a short to voltage on a fuel injector circuit. If the test lamp illuminates, a short to voltage is the cause of the condition.
10. 12 This step isolates which circuit is causing the condition. If the test lamp turns OFF when a multi-way connector is disconnected, test the affected circuits for a short to voltage.
11. 13 This step tests if a ground is constantly being applied to the fuel injectors.
12. 14 This step isolates which circuit is causing the condition. If the test lamp turns OFF when a multi-way connector is disconnected, test the affected circuits for a short to ground.
13. 15 This step tests for an open circuit. If the DMM displays OL on all of the fuel injector circuits, the ignition voltage circuit is open.
14. 16 This step tests for an open circuit. If the DMM displays OL on one of the fuel injector circuits, the fuel injector command circuit is open.
15. 17 This step tests for excessive resistance in a fuel injector circuit.
16. 18 This step is testing for a short between the ignition feed circuit, and the fuel injector command circuit. If the resistance of the circuits is less than 0.3ohms, test for a short between the circuits. If a short cannot be found, the fuel injector may be the cause of the condition. The normal fuel injector resistance is between 0.3-0.4 ohms.
17. 19 This step tests for a short to voltage on a fuel injector circuit. If the test lamp illuminates, a short to voltage is the cause of the condition.
18. 20 This step isolates which circuit is causing the condition. If the test lamp turns OFF when a multi-way connector is disconnected, test the affected circuits for a short to voltage.

The boost sensor responds to pressure changes in the intake manifold. This pressure is created by the turbocharger and changes with Accelerator Pedal Position (APP) and engine speed. The Engine Control Module (ECM) uses this information to provide engine overboost protection. The boost sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The ECM supplies 5 volts to the boost sensor on the 5-volt reference 2 circuit, and provides a ground on a low reference circuit. The boost sensor provides a signal to the ECM on a signal circuit relative to the pressure changes. The ECM monitors the boost sensor signal for voltage outside of the normal range. The ECM calculates a predicted value for the boost sensor. The ECM then compares the predicted value to the actual signal. This DTC will set if the boost pressure signal is above the predicted range.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 With the ignition ON and the engine OFF, the BARO sensor and the boost sensor should indicate the current barometric pressure. A significant difference between the readings indicates an electrical fault.
2. 5 This step tests the wastegate actuator diaphragm for a leak.
3. 6 This step tests the wastegate actuator, the linkage, and the wastegate for proper operation.

The boost sensor responds to pressure changes in the intake manifold. This pressure is created by the turbocharger and changes with Accelerator Pedal Position (APP) and engine speed. The Engine Control Module (ECM) uses this information to assist in diagnosis of the Barometric (BARO) pressure sensor and to provide engine overboost protection. The boost sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The ECM supplies 5 volts to the boost sensor on the 5-volt reference 2 circuit, and provides a ground on a low reference circuit. The boost sensor provides a signal to the ECM on a signal circuit relative to the pressure changes. The ECM monitors the boost sensor signal for voltage outside of the normal range. The ECM calculates a predicted value for the boost sensor. The ECM then compares the predicted value to the actual signal. This DTC will set if the boost sensor signal is above the predicted range.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 With the ignition ON and the engine OFF, the BARO sensor and the boost sensor should indicate the current barometric pressure. A significant difference between the readings indicates an electrical fault.
2. 5 This step tests the wastegate actuator diaphragm for a leak.
3. 6 This step tests the wastegate actuator, the linkage, and the wastegate for proper operation.

The boost sensor responds to pressure changes in the intake manifold. This pressure is created by the turbocharger and changes with Accelerator Pedal Position (APP) and engine speed. The Engine Control Module (ECM) uses this information to provide engine overboost protection. The boost sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The ECM supplies 5 volts to the boost sensor on the 5-volt reference 2 circuit, and provides a ground on a low reference circuit. The boost sensor provides a signal to the ECM on a signal circuit relative to the pressure changes. The ECM monitors the boost sensor signal for voltage outside of the normal range. The ECM calculates a predicted value for the boost sensor. The ECM then compares the predicted value to the actual signal. This DTC will set if the boost sensor signal is below the predicted range.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 With the ignition ON and the engine OFF, the BARO sensor and the boost sensor should indicate the current barometric pressure. A significant difference between the readings indicates an electrical fault.
2. 7 The spring in the wastegate actuator should return the wastegate via the linkage back to the closed position.

The boost sensor responds to pressure changes in the intake manifold. This pressure is created by the turbocharger and changes with Accelerator Pedal Position (APP) and engine speed. The Engine Control Module (ECM) uses this information to assist in diagnosis of the Barometric (BARO) pressure sensor and to provide engine overboost protection. The boost sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The ECM supplies 5 volts to the boost sensor on the 5-volt reference 2 circuit, and provides a ground on a low reference circuit. The boost sensor provides a signal to the ECM on a signal circuit relative to the pressure changes. The ECM monitors the boost sensor signal for voltage outside of the normal range. The ECM calculates a predicted value for the boost sensor. The ECM then compares the predicted value to the actual signal. This DTC will set if the boost sensor signal is below the predicted range.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 With the ignition ON and the engine OFF, the BARO sensor and the boost sensor should indicate the current barometric pressure. A significant difference between the readings indicates an electrical fault.
2. 7 The spring in the wastegate actuator should return the wastegate via the linkage back to the closed position.

The boost sensor responds to pressure changes in the intake manifold. This pressure is created by the turbocharger and changes with Accelerator Pedal Position (APP) and engine speed. The Engine Control Module (ECM) uses this information to provide engine overboost protection. The boost sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The ECM supplies 5 volts to the boost sensor on the 5-volt reference 2 circuit, and provides a ground on a low reference circuit. The boost sensor provides a signal to the ECM on a signal circuit relative to the pressure changes. The ECM monitors the boost sensor signal for voltage outside of the normal range. If the ECM detects a boost sensor signal voltage that is excessively low, this DTC will set.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 The boost sensor 5-volt reference circuit is shared with other sensors. If DTC P1639 is set, this indicates that the 5-volt reference circuit is shorted to ground and should be diagnosed first. The short may be on another sensor 5-volt reference circuit.
2. 4 Operate the vehicle within the same conditions as when the DTC failed. If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data can aid in locating an intermittent condition.

The boost sensor responds to pressure changes in the intake manifold. This pressure is created by the turbocharger and changes with Accelerator Pedal Position (APP) and engine speed. The Engine Control Module (ECM) uses this information to assist in diagnosis of the Barometric (BARO) pressure sensor and to provide engine overboost protection. The boost sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The ECM supplies 5 volts to the boost sensor on the 5-volt reference 2 circuit, and provides a ground on a low reference circuit. The boost sensor provides a signal to the ECM on a signal circuit relative to the pressure changes. The ECM monitors the boost sensor signal for voltage outside of the normal range. If the ECM detects a boost sensor signal voltage that is excessively low, this DTC will set.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 The boost sensor 5-volt reference circuit is shared with other sensors. If DTC P1639 is set, this indicates that the 5-volt reference circuit is shorted to ground and should be diagnosed first. The short may be on another sensor 5-volt reference circuit.
2. 4 Operate the vehicle within the same conditions as when the DTC failed. If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data can aid in locating an intermittent condition.

The boost sensor responds to pressure changes in the intake manifold. This pressure is created by the turbocharger and changes with Accelerator Pedal Position (APP) and engine speed. The Engine Control Module (ECM) uses this information to provide engine overboost protection. The boost sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The ECM supplies 5 volts to the boost sensor on the 5-volt reference 2 circuit, and provides a ground on a low reference circuit. The boost sensor provides a signal to the ECM on a signal circuit relative to the pressure changes. The ECM monitors the boost sensor signal for voltage outside of the normal range. If the ECM detects a boost sensor signal voltage that is excessively high, this DTC will set.

The number below refers to the step number in the diagnostic procedures.

1. 3 Operate the vehicle within the same conditions as when the DTC failed. If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data can aid in locating an intermittent condition.

The boost sensor responds to pressure changes in the intake manifold. This pressure is created by the turbocharger and changes with Accelerator Pedal Position (APP) and engine speed. The Engine Control Module (ECM) uses this information to assist in diagnosis of the Barometric (BARO) pressure sensor and to provide engine overboost protection. The boost sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The ECM supplies 5 volts to the boost sensor on the 5-volt reference 2 circuit, and provides a ground on a low reference circuit. The boost sensor provides a signal to the ECM on a signal circuit relative to the pressure changes. The ECM monitors the boost sensor signal for voltage outside of the normal range. If the ECM detects a boost sensor signal voltage that is excessively high, this DTC will set.

The number below refers to the step number in the diagnostic procedures.

1. 3 Operate the vehicle within the same conditions as when the DTC failed. If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data can aid in locating an intermittent condition.

The ECM adjusts the fuel delivery to each cylinder in order to minimize crankshaft speed changes. If the ECM identifies a cylinder or cylinders requiring an excessive amount of fuel in order to maintain the correct crankshaft speed, DTC P0300 will set.

The Engine Control Module (ECM) monitors changes in crankshaft speed using inputs from the Crankshaft Position (CKP) sensor and the Fuel Injection Control Module (FICM). The ECM adjusts the fuel delivery to each cylinder in order to minimize crankshaft speed changes. This DTC will set when the ECM identifies a cylinder or cylinders requiring an excessive amount of fuel in order to maintain the correct crankshaft speed.

The Hall Effect Crankshaft Position (CKP) sensor signal indicates the crankshaft speed and position. There are 57 teeth on the front of the crankshaft sprocket, plus a sync gap. The CKP sensor will output an ON-OFF pulse as each window passes the sensing element. The CKP sensor is connected directly to the Engine Control Module (ECM) by the following circuits

1. The 12-volt reference circuit.
2. The low reference circuit.
3. The CKP sensor signal circuit.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 This step determines if the fault is present.
2. 6 This step simulates a CKP sensor signal to the ECM. If the ECM receives the signal, the fuel pump will operate for about two seconds.
3. 11 The CKP system variation learn procedure must be performed anytime the relationship between the CKP sensor and the CKP reluctor wheel is changed.
4. 13 The CKP system variation learn procedure must be performed anytime the relationship between the CKP sensor and the CKP reluctor wheel is changed.

The Hall Effect Crankshaft Position (CKP) sensor signal indicates the crankshaft speed and position. There are 57 teeth on the front of the crankshaft sprocket, plus a sync gap. The CKP sensor will output an ON-OFF pulse as each window passes the sensing element. The CKP sensor is connected directly to the Engine Control Module (ECM) by the following circuits

1. The 12-volt reference circuit.
2. The low reference circuit.
3. The CKP sensor signal circuit.

The Hall Effect Camshaft Position (CMP) sensor produces 3 ON-OFF pulses for each revolution of the camshaft. The CMP output is pulse width encoded. The Engine Control Module (ECM) uses the CMP and Crankshaft Position (CKP) output pulses to determine the engine speed and position. The CMP is connected directly to the ECM by the following circuits

1. 12-volt reference.
2. Low reference.
3. CMP sensor signal.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 If the engine starts and runs, the condition is suspected to be intermittent. If there is a condition with the CMP sensor circuit the vehicle will not run.
2. 6 This step determines if the CMP sensor is working correctly.
3. 13 Inspect the CMP sensor for physical damage. The camshaft may damage the sensor.

The Hall Effect Camshaft Position (CMP) sensor produces 3 ON-OFF pulses for each revolution of the camshaft. The CMP output is pulse width encoded. The Engine Control Module (ECM) uses the CMP and Crankshaft Position (CKP) output pulses to determine the engine speed and position. The CMP is connected directly to the ECM by the following circuits

1. 12-volt reference.
2. Low reference.
3. CMP sensor signal.

The Engine Control Module (ECM) replicates the signal received from the Crankshaft Position (CKP) sensor. This signal is sent to the fuel injection control module (FICM) through the engine speed signal circuit. The FICM uses this replicated signal to generate injection current and control the recharge of the fuel injection high voltage circuits. When cranking, the FICM has full control of the fuel injectors. The only input the FICM uses at this time is the engine speed signal from the ECM. The FICM monitors the signal along with the injection request signals from the ECM after the engine is running. If there is a problem with this signal, a DTC could set.

The glow plug system is used to assist in providing the heat required to begin combustion during cold engine temperatures. The glow plugs are heated before and during cranking, as well as initial engine operation. The Engine Control Module (ECM) controls the glow plug ON times by monitoring coolant temperature and glow plug voltage. The California Glow Plug system has eight individual glow plug supply circuits between the controller and the glow plugs. If the feedback voltage from the controller to the ECM is not within range, DTC P0380 will set.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 4 This step will determine if DTC P0380 is a hard failure.
2. 5 This step will determine if there is a short to voltage on the signal circuit.
3. 9 This step will determine if there is ignition voltage at the glow plug relay.
4. 11 This step will determine if the glow plug control circuit and ECM are working properly.
5. 12 This step will determine if there is a short to voltage on the relay control circuit.
6. 14 This step will determine if the glow plugs or the glow plug harness is causing the DTC P0380.

The glow plug system is used to assist in providing the heat required to begin combustion during cold engine temperatures. The glow plugs are heated before and during cranking, as well as initial engine operation. The Engine Control Module (ECM) controls the glow plug ON times by monitoring coolant temperature and glow plug voltage.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 This step will determine if DTC P0380 is a hard failure.
2. 3 This step will determine if the ECM is requesting the glow plug system ON.

The Engine Control Module (ECM) uses the Mass Air Flow (MAF) sensor signal to calculate the amount of Exhaust Gas Recirculation (EGR) flow. The ECM will control the EGR valve vacuum control solenoid and the EGR vacuum vent solenoid to allow vacuum to operate the EGR valve. The EGR control system uses vacuum from a belt driven mechanical pump called a vacuum pump. Diesel engines do not create enough engine vacuum on their own to allow the EGR gases into the combustion process. When the ECM commands the EGR valve to open, the EGR throttle valve will be commanded closed. The EGR throttle valve creates a restriction of incoming fresh air to the engine in order to create engine vacuum. If the ECM detects a calibrated difference between the desired MAF rate and the actual MAF rate during EGR system operation, DTC P0401 sets.

The Exhaust Gas Recirculation (EGR) valve is vacuum operated. Vacuum for the EGR valve control system is supplied by a belt driven vacuum pump. The EGR valve vacuum control solenoid and the EGR valve vacuum vent solenoid work together to control the position of the EGR valve. The Engine Control Module (ECM) monitors the EGR vacuum sensor signal to determine the amount of vacuum that is applied to the EGR valve. The ECM uses the Mass Air Flow (MAF) sensor to calculate the amount of exhaust gas that is consumed by the engine. When the EGR valve is opened, the MAF rate will decrease. If the EGR vacuum sensor signal is lower than desired and the MAF rate is higher than expected, it is assumed that the EGR valve is not opening enough due to a vacuum problem and Diagnostic Trouble Code (DTC) P0404 sets.

The Exhaust Gas Recirculation (EGR) vacuum sensor is used to monitor the amount of vacuum that is available to the EGR valve. A low reference circuit, 5-volt reference circuit and a vacuum sensor signal circuit are used to interface the ECM with the EGR vacuum sensor. If the EGR vacuum sensor signal voltage is pulled below a calibrated value, DTC P0405 sets.

The Exhaust Gas Recirculation (EGR) vacuum sensor is used to monitor the amount of vacuum that is available to the EGR valve. A low reference circuit, 5-volt reference circuit and a vacuum sensor signal circuit are used to interface the ECM with the EGR vacuum sensor. If the EGR vacuum sensor signal voltage is above a calibrated value, DTC P0406 sets.

The number below refers to the step number in the diagnostic procedures.

1. 2 If DTC P1639 sets, there is a short to voltage on the 5-volt reference circuit. Perform the DTC P1639 diagnostic before proceeding. See «DTC P1639: 5-VOLT REFERENCE 2 CIRCUIT»(ref-138411-S29319932602002041200000) .

The Exhaust Gas Recirculation (EGR) valve is vacuum operated. Vacuum for the EGR valve control system is supplied by a belt driven vacuum pump. The EGR valve vacuum control solenoid and the EGR valve vacuum vent solenoid work together to control the position of the EGR valve. The EGR valve vacuum control solenoid is supplied with 12 volts through the ignition 1 circuit. The EGR valve vacuum control solenoid is pulse width modulated through the EGR valve solenoid control circuit by the Engine Control Module (ECM). The ECM monitors the voltage on the EGR valve vacuum solenoid control circuit. If the ECM detects a low voltage condition on this circuit, DTC P0489 sets.

The Exhaust Gas Recirculation (EGR) valve is vacuum operated. Vacuum for the EGR valve control system is supplied by a belt driven vacuum pump. The EGR valve vacuum control solenoid and the EGR valve vacuum vent solenoid work together to control the position of the EGR valve. The EGR valve vacuum control solenoid is supplied with 12 volts through the ignition 1 circuit. The EGR valve vacuum control solenoid is pulse width modulated through the EGR valve vacuum solenoid control circuit by the Engine Control Module (ECM). The ECM monitors the voltage on the EGR valve vacuum solenoid control circuit. If the ECM detects a high voltage condition on this circuit, Diagnostic Trouble Code (DTC) P0490 sets.

The Vehicle Speed Sensor (VSS) monitors the rotation speed of the transmission output shaft. The VSS assembly is a permanent magnet generator. It produces an AC voltage as the rotor teeth on the output shaft of the transmission, 2WD, or transfer case, 4WD, pass through the sensor's magnetic field. The AC voltage frequency and amplitude increase as the vehicle speed increases. The TCM will send a controlled duty cycle voltage to the Engine Control Module (ECM) that operates in a range of -4.5 volts or +5.0 volts. The ECM converts this signal into vehicle speed. As vehicle speed increases, the frequency of the duty cycle will increase.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 4 This step tests the TCM and circuit 400 for voltage at the ECM connector.
2. 5 This step tests for continuity and a short to ground in the wiring system between the TCM and ECM.

The Vehicle Speed Sensor (VSS) assembly provides vehicle speed information to the Engine Control Module (ECM). The VSS assembly is a permanent magnet generator. The VSS produces alternating current (AC) as the rotor teeth on the output shaft of the transmission (2WD) or transfer case (4WD) pass through the magnetic field of the sensor. The frequency and amplitude of the AC waveform increase as vehicle speed increases. If the ECM detects no vehicle speed for a specified length of time, while other sensors indicate that the vehicle is moving, DTC P0500 sets.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 5 The resistance measurement will not change if either the VSS high signal circuit or the VSS low signal circuit, but not both, is shorted to ground. The vehicle speed detector in the ECM and the VSS are matched in such a way that an open or a short to ground in the VSS low signal circuit will not usually cause a loss of speed signal or a DTC P0500 to set. The lower resistance value given represents the nominal resistance specification of the VSS at -40°F (-40°C), minus the manufacturing tolerance specification of 10 percent. The higher resistance value given represents the nominal resistance specification of the VSS at 302°F (150°C), plus the manufacturing tolerance specification of 10 percent.
2. 8 This step isolates the short between the VSS and the wiring.
3. 10 Do not skip step 7 . The Digital Multimeter (DMM) will detect AC voltage if the VSS high signal circuit is shorted to ground.
4. 13 The replacement ECM must be programmed and the crankshaft position system variation procedure must be performed. See «ENGINE CONTROL MODULE»(ref-138411-S14665279672002041200000) under PROGRAMMING.

The Engine Control Module (ECM) uses an Intake Air Heater (IAH) to warm the incoming air for proper cylinder combustion. The ECM grounds the control coil of the IAH relay to energize the heater during cold operation. If the ECM detects voltage on the IAH circuit when the relay is commanded OFF, or incorrect voltage when the relay is commanded ON, a DTC will set.

The numbers below refer to step numbers in the diagnostic procedures.

1. 3 The IAH relay is only commanded ON for 5 seconds when there is an active DTC fault.
2. 4 This step checks for battery voltage output from the IAH relay to the IAH.
3. 6 The IAH relay is only commanded ON for 5 seconds when there is an active DTC fault.

The Engine Control Module (ECM) uses an Intake Air Heater (IAH) to warm the incoming air for proper cylinder combustion. The ECM grounds the control coil of the IAH relay to energize the heater during cold operation. The ECM sends a bias voltage on diagnostic circuits 1 and 2. If this voltage is not pulled low when the relay is OFF, or is not high with the relay ON, DTC P0543 will set.

This diagnostic applies to internal microprocessor integrity conditions within the Engine Control Module (ECM). This diagnostic also addresses if the ECM is not programmed. The following DTCs are diagnosed in this DTC test

1. DTC P0601 Control Module Read Only Memory (ROM).
2. DTC P0602 Control Module Not Programmed.
3. DTC P0603 Control Module Long Term Memory Reset.
4. DTC P0604 Control Module Random Access Memory (RAM).
5. DTC P1621 Control Module Long Term Memory Performance.
6. DTC P1683 Control Module Ignition Off Timer Performance.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 A DTC P0602 indicates the ECM is not programmed.
2. 4 Attempt to program the ECM. If the ECM fails to program a second time, replace the ECM.

The Fuel Injection Control Module (FICM) has the ability to perform internal circuit checks on the FICM microprocessor, status of the monitoring module, and status of the FICM A/D conversion module. If the FICM senses a problem in the FICM circuits, the FICM will send an error message to the Engine Control Module (ECM). If this condition exists, DTC P0611 will set.

The Engine Control Module (ECM) monitors the condition of the ignition relay control circuit. If the ECM senses excessive voltage on this circuit, DTC P0612 will set.

Ignition voltage is supplied directly to the Malfunction Indicator Lamp (MIL). The Engine Control Module (ECM) controls the lamp by grounding the control circuit via an internal switch called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line which is monitored by the ECM. When the ECM is commanding a component ON, the voltage of the control circuit should be low, near 0 volts. When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be high, near battery voltage. If the fault detection circuit senses a voltage other than what is expected, the fault line status will change causing the DTC to set.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 5 This step tests for a short to ground in the MIL control circuit. With the ECM disconnected and the ignition ON the MIL should be OFF.
2. 6 This step tests for a short to voltage on the MIL control circuit. With the fuse removed there should be no voltage on the MIL control circuit.
3. 17 This vehicle is equipped with a ECM that utilizes an electrically erasable programmable read only memory (EEPROM). When the ECM is being replaced, the new ECM must be programed.

The Malfunction Indicator Lamp (MIL) request circuit signals the Engine Control Module (ECM) that the transmission control module (TCM) is requesting MIL illumination.

The number below refers to the step number in the diagnostic procedures.

1. 2 If the TCM has DTCs set that are requesting MIL illumination, those DTCs must be diagnosed first.

A mechanical switch attached to the brake pedal sends a signal to the Transmission Control Module (TCM) indicating the service brake has been applied. This signal is either ignition voltage or a ground signal depending on the calibration installed in the TCM.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 This step tests brake switch status.
2. 4 This step tests for voltage at the C1 connector.
3. 5 This step tests for voltage after the stop lamp switch.
4. 6 This step tests for voltage before the stop lamp switch.

Battery voltage is supplied from the brake fuse to the clutch switch. The clutch switch is a normally-closed switch. When the clutch pedal is released, the clutch pedal position switch signal circuit is pulled up to battery voltage. When the clutch pedal is applied, the switch opens, and the voltage drops to 0 volts. If the Engine Control Module (ECM) detects a specified number of vehicle speed transitions without detecting a clutch switch transition, DTC P0704 will set.

The installation of a transmission-mounted neutral start/reverse signal switch is required. This switch, commonly called a Park/Neutral Position (PNP) switch, mounts directly onto the transmission housing from the outside and detects the angular position of the shift selector shaft. This position is communicated to the Transmission Control Module (TCM) so that certain vehicle control functions can be coordinated with the position of the shift controls. The PNP switch has redundant circuitry to alert the TCM in the event of a single wire or switch failure. The neutral signal output of the PNP switch is typically used as confirmation that the transmission is in neutral before the engine starter is engaged. The PNP switch is interfaced to the starter circuit with weatherproof electrical connectors. The reverse signal provision may be used to activate vehicle back-up lights and/or reverse warning devices.

The numbers below refer to the step numbers n the diagnostic procedures.

1. 3 This step tests PNP switch status.
2. 4 This step tests TCM input response.
3. 5 This step tests the wiring harness for opens or shorts.

The Engine Control Module (ECM) uses the Fuel Rail Pressure (FRP) sensor to determine fuel pressure to the fuel injectors. This is then compared to the calculated target fuel pressure as determined by the ECM. The ECM adjusts the FRP by modulating the duty cycle of the control driver of the fuel pressure regulator. Injector pulse duration is determined by the measured rail pressure and the target injection fuel into each cylinder. If a sensor circuit malfunction is detected, or the commanded fuel injection pump flow is not within the proper range for a given engine load and speed, DTC will be set.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 If the fuel temperature is high enough to set DTC P0168, the fuel may be thin enough to cause this DTC to set.
2. 3 The engine will not start if the fuel leak is large enough.
3. 4 This step checks for an inaccurate fuel rail pressure sensor.
4. 5 This step checks for a restriction in the fuel system between the fuel injection pump and the fuel tank.
5. 6 This test checks to see if the fuel injection pump is able to supply maximum fuel pressure at idle. The fuel injection pump should be able to create 145-158 MPa at idle. At higher ambient temperatures, the fuel pressure will be lower, but still more than 145 MPa.
6. 7 This step checks for a restriction in the fuel system between the fuel injection pump and the fuel tank that may only cause symptoms at higher engine speed and load conditions.
7. 9 This step checks to see if the fuel rail pressure sensor wiring and ECM are functioning normally.
8. 11 If the vacuum is still too high in the fuel supply system after replacing the fuel filter, there is a restriction in the fuel supply lines or sending unit in the fuel tank.

The Engine Control Module (ECM) uses the Fuel Rail Pressure (FRP) sensor to determine fuel pressure to the fuel injectors. This is then compared to the calculated target fuel pressure as determined by the ECM. The ECM adjusts the FRP by modulating the duty cycle of the control driver of the fuel pressure regulator. Injector pulse duration is determined by the measured rail pressure and the target injection fuel into each cylinder. If a sensor circuit malfunction is detected, or the commanded fuel injection pump flow is not within the proper range for a given engine load and speed, DTC will be set.

The Accelerator Pedal Position (APP) sensor is mounted on the accelerator pedal control assembly. The sensor is made up of 3 individual sensors within one housing. Three separate signal, low reference, and 5-volt reference circuits are used in order to interface the APP sensor with the ECM. Each sensor has a unique functionality to determine pedal position. See APP SENSOR POSITION VOLTAGE table. The Engine Control Module (ECM) uses the APP sensor to determine the amount of acceleration or deceleration desired by the person driving the vehicle via fuel injector control. This Diagnostic Trouble Code (DTC) sets if the ECM detects a condition with more than one sensor within the APP sensor.

APP SENSOR POSITION VOLTAGE

The secondary fuel pump is located in the rear fuel tank. The secondary fuel pump is powered by a secondary fuel pump relay. Fuel is transferred from the rear fuel tank to the front fuel tank in order to ensure all of the usable fuel volume is available to the primary fuel pump. The secondary fuel pump relay supply voltage is received from the primary fuel pump relay when the primary fuel pump is energized. This DTC sets when the Engine Control Module (ECM) commands the secondary fuel pump ON and a predetermined change in both the front and rear fuel level sensors does not occur.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 This step determines if the condition is on the coil side, or the switch side of the fuel pump relay. Listen for an audible click as the fuel pump relay is commanded ON and OFF. Repeat the commands as necessary in order to verify the fuel pump relay operation.
2. 4 This step tests the control circuit of the fuel pump relay. The test lamp should turn ON and OFF with the scan tool commands. Repeat the commands as necessary.
3. 8 This step verifies the fuel pump operation. Listen for the fuel pump as you command the fuel pump ON. Repeat the commands as necessary in order to verify the fuel pump operation.
4. 9 This step tests the ignition voltage circuit of the fuel pump relay.
5. 10 This step verifies the fuel pump operation. If the test lamp blinks, then the fuel pump and circuits are okay.
6. 13 The rear fuel level sensor voltage must be above the specified value in order to continue with the diagnostic procedure.
7. 15 This step tests for a fuel flow condition. If the rear fuel level sensor voltage does not decrease as the fuel pump is operating, a restriction in the fuel lines or rear sender is the probable cause of the DTC.
8. 16 If a restriction in the fuel lines, or rear fuel sender is not isolated, a mechanical condition exists in the fuel pump. Replace the fuel pump.

The Mass Air Flow (MAF) sensor measures the amount of air entering the engine during a given time. The Engine Control Module (ECM) uses the MAF sensor information to monitor Exhaust Gas Recirculation (EGR) flow rate. A large quantity of air entering the engine indicates an acceleration or high load situation, while a small quantity of air indicates deceleration or idle. The ECM has the ability to determine an intake leak by using the MAF sensor and the EGR control pressure sensor.

The number below refers to the step number in the diagnostic procedures.

1. 3 A large leak in the intake system will set a MAF sensor DTC. All intake ducts should be checked after the MAF sensor for proper installation.

The Engine Control Module (ECM) enables the appropriate fuel injector on the compression stroke for each cylinder. The ECM controls the Fuel Injection Control Module (FICM) by grounding the control circuit via a solid state device called a driver. The ECM monitors the state of the driver. If the ECM detects an incorrect voltage for the commanded state of an injector driver, DTCs P1223, P1226, P1229, P1232, P1235, P1238, P1241, or P1244 will set.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 4 This step determines how many fuel injector control circuit DTCs are set. If there is only 1 fuel injector DTC set, an open circuit, or poor connection is likely the cause of the concern. To determine which cylinder is causing the condition, see «DIAGNOSTIC AIDS»(ref-138411-S11012152322002050200000) .
2. 5 This step determines if there are 4 or 8 fuel injector control circuit DTCs are set. A short to ground will set 4 fuel injector control circuit DTCs for cylinders 2, 3, 5, 8, or cylinders 1, 4, 6, 7. To determine which cylinders are affected, see «DIAGNOSTIC AIDS»(ref-138411-S11012152322002050200000) . If there are 8 fuel injector control circuit DTCs set, a short to voltage on a fuel injector control circuit is likely the cause of the concern. A short to voltage will set all 8 of the fuel injector control circuit DTCs.
3. 6 This step verifies the FICM is supplying the appropriate voltage to the control circuit. If the Digital Multimeter (DMM) displays 5 volts, inspect for a poor connection at the ECM.
4. 8 This step is testing for a short to ground on a fuel injector control circuit. If the test lamp illuminates on any fuel injector control circuit, a short to ground is the cause of the condition.
5. 9 This step is testing for a short to a voltage. If the DMM displays a voltage greater than the specified value, a short to voltage is the cause of the condition.

The Fuel Injection Control Module (FICM) supplies high voltage to each fuel injector on the ignition voltage circuits. The FICM energizes each fuel injector by grounding the command circuit between the FICM and the fuel injector. The FICM monitors the status of the ignition voltage circuits and the fuel injector command circuits. When a fuel injector circuit condition is detected by the FICM, all of the fuel injectors on the affected ignition voltage circuit will be disabled. If a circuit condition is detected on a fuel injector circuit for cylinders 1, 4, 6, or 7, DTCs P0201, P0204, P0206, P0207 will set, along with DTC P1261. If a circuit condition is detected on a fuel injector circuit for cylinders 2, 3, 5, or 8, DTCs P0202, P0203, P0205, P0208 will set, along with DTC P1262.

The number below refers to the step number in the diagnostic procedures.

1. 2 This step determines if a wiring or injector problem caused this DTC to set. If DTC P1261 set alone, an internal FICM fault is the cause.

The Fuel Injection Control Module (FICM) supplies high voltage to each fuel injector on the ignition voltage circuits. The FICM energizes each fuel injector by grounding the command circuit between the FICM and the fuel injector. The FICM monitors the status of the ignition voltage circuits and the fuel injector command circuits. When a fuel injector circuit condition is detected by the FICM, all of the fuel injectors on the affected ignition voltage circuit will be disabled. If a circuit condition is detected on a fuel injector circuit for cylinders 1, 4, 6, or 7, DTCs P0201, P0204, P0206, P0207 will set, along with DTC P1261. If a circuit condition is detected on a fuel injector circuit for cylinders 2, 3, 5, or 8, DTCs P0202, P0203, P0205, P0208 will set, along with DTC P1262.

The number below refers to the step number in the diagnostic procedures.

1. 2 This step determines if a wiring or injector problem caused this DTC to set. If DTC P1262 sets alone, an internal FICM fault is the cause.

The Engine Control Module (ECM) reads analog data from the Accelerator Pedal Position (APP) sensor and processes the analog data into digital data in order to interface with the powertrain software. If the ECM microprocessor can not perform this task then this DTC will set.

The Accelerator Pedal Position (APP) sensor is mounted on the accelerator pedal control assembly. The sensor is made up of 3 individual sensors within 1 housing. Three separate signal, low reference, and 5-volt reference circuits are used in order to interface the APP sensor with the Engine Control Module (ECM). Each sensor has a unique functionality to determine pedal position. See APP SENSOR POSITION VOLTAGE table. The ECM uses the APP sensor to determine the amount of acceleration or deceleration desired by the person driving the vehicle via fuel injector control. This DTC sets if the ECM determines an out of range condition with the APP sensor.

APP SENSOR POSITION VOLTAGE

The Accelerator Pedal Position (APP) sensor is mounted on the accelerator pedal control assembly. The sensor is made up of 3 individual sensors within 1 housing. Three separate signal, low reference, and 5-volt reference circuits are used in order to interface the APP sensor with the Engine Control Module (ECM). Each sensor has a unique functionality to determine pedal position. See APP SENSOR POSITION VOLTAGE table under DTC P1271: APP SENSOR 1-2 PERFORMANCE. The ECM uses the APP sensor to determine the amount of acceleration or deceleration desired by the person driving the vehicle via fuel injector control. This DTC sets if the ECM determines an out of range condition with the APP sensor.

The Accelerator Pedal Position (APP) sensor is mounted on the accelerator pedal control assembly. The sensor is made up of 3 individual sensors within one housing. Three separate signal, low reference, and 5-volt reference circuits are used in order to interface the APP sensor with the Engine Control Module (ECM). Each sensor has a unique functionality to determine pedal position. See APP SENSOR POSITION VOLTAGE table under DTC P1271: APP SENSOR 1-2 PERFORMANCE. The ECM uses the APP sensor to determine the amount of acceleration or deceleration desired by the person driving the vehicle via fuel injector control. This DTC sets if the ECM determines an out of range condition with the APP sensor.

The Accelerator Pedal Position (APP) sensor is mounted on the accelerator pedal control assembly. The sensor is made up of 3 individual sensors within 1 housing. Three separate signal, low reference, and 5-volt reference circuits are used in order to interface the APP sensor with the Engine Control Module (ECM). Each sensor has a unique functionality to determine pedal position. See APP SENSOR POSITION VOLTAGE table under DTC P1271: APP SENSOR 1-2 PERFORMANCE. The ECM uses the APP sensor to determine the amount of acceleration or deceleration desired by the person driving the vehicle via fuel injector control. This DTC sets if the ECM determines an out of range condition with the APP sensor.

The Accelerator Pedal Position (APP) sensor is mounted on the accelerator pedal control assembly. The sensor is made up of 3 individual sensors within 1 housing. Three separate signal, low reference, and 5-volt reference circuits are used in order to interface the APP sensor with the Engine Control Module (ECM). Each sensor has a unique functionality to determine pedal position. See APP SENSOR POSITION VOLTAGE table under DTC P1271: APP SENSOR 1-2 PERFORMANCE. The ECM uses the APP sensor to determine the amount of acceleration or deceleration desired by the person driving the vehicle via fuel injector control. This DTC sets if the ECM determines an out of range condition with the APP sensor.

The Accelerator Pedal Position (APP) sensor is mounted on the accelerator pedal control assembly. The sensor is made up of 3 individual sensors within 1 housing. Three separate signal, low reference, and 5-volt reference circuits are used in order to interface the APP sensor with the Engine Control Module (ECM). Each sensor has a unique functionality to determine pedal position. See APP SENSOR POSITION VOLTAGE table under DTC P1271: APP SENSOR 1-2 PERFORMANCE. The ECM uses the APP sensor to determine the amount of acceleration or deceleration desired by the person driving the vehicle via fuel injector control. This DTC sets if the ECM determines an out of range condition with the APP sensor.

The Accelerator Pedal Position (APP) sensor is mounted on the accelerator pedal control assembly. The sensor is made up of 3 individual sensors within 1 housing. Three separate signal, low reference, and 5-volt reference circuits are used in order to interface the APP sensor with the Engine Control Module (ECM). Each sensor has a unique functionality to determine pedal position. See APP SENSOR POSITION VOLTAGE table under DTC P1271: APP SENSOR 1-2 PERFORMANCE. The ECM uses the APP sensor to determine the amount of acceleration or deceleration desired by the person driving the vehicle via fuel injector control. This DTC sets if the ECM determines an out of range condition with the APP sensor.

The Accelerator Pedal Position (APP) sensor is mounted on the accelerator pedal control assembly. The sensor is made up of 3 individual sensors within 1 housing. Three separate signal, low reference, and 5-volt reference circuits are used in order to interface the APP sensor with the Engine Control Module (ECM). Each sensor has a unique functionality to determine pedal position. See APP SENSOR POSITION VOLTAGE table under DTC P1271: APP SENSOR 1-2 PERFORMANCE. The ECM uses the APP sensor to determine the amount of acceleration or deceleration desired by the person driving the vehicle via fuel injector control. This DTC sets if the ECM determines an out of range condition with the APP sensor.

The Accelerator Pedal Position (APP) sensor is mounted on the accelerator pedal control assembly. The sensor is made up of 3 individual sensors within 1 housing. Three separate signal, low reference, and 5-volt reference circuits are used in order to interface the APP sensor with the Engine Control Module (ECM). Each sensor has a unique functionality to determine pedal position. See APP SENSOR POSITION VOLTAGE table under DTC P1271: APP SENSOR 1-2 PERFORMANCE. The ECM uses the APP sensor to determine the amount of acceleration or deceleration desired by the person driving the vehicle via fuel injector control. This DTC sets if the ECM determines an out of range condition with the APP sensor.

The Engine Control Module (ECM) monitors the Crankshaft Position (CKP) and the Camshaft Position (CMP) signals to determine if they are synchronized. If both signals are not observed by the ECM within a narrow time window, the ECM will determine that an error has occurred and DTC P1345 will set.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 A condition that sets one of these DTCs may also result in a DTC P1345. Diagnose these codes before continuing with this diagnostic.
2. 4 A loose CMP sensor may result in a DTC P1345. Attempt to tighten the sensor to proper torque specifications. If unable to prevent CMP sensor movement, inspect the cover for damage before replacing the sensor.
3. 5 A cracked CMP sensor or internal breakage could result in DTC P1345. This will not be apparent unless the sensor is removed from the front engine cover.
4. 6 If the CMP sensor appears to be damaged by contact with the camshaft gear, you may need to remove the front engine cover and inspect for excessive camshaft end-play.

The Exhaust Gas Recirculation (EGR) valve is vacuum operated. Vacuum for the EGR valve control system is supplied by a belt driven vacuum pump. The EGR valve vacuum control solenoid and the EGR valve vacuum vent solenoid work together to control the position of the EGR valve. The Engine Control Module (ECM) monitors the EGR vacuum sensor signal to determine the amount of vacuum that is applied to the EGR valve. The ECM uses the Mass Air Flow (MAF) sensor to calculate the amount of exhaust gas that is consumed by the engine. When the EGR valve is opened, the MAF rate will decrease. If the EGR vacuum sensor signal is higher than desired and the MAF rate is lower than expected, it is assumed that the EGR valve is not closing due to a vacuum problem and Diagnostic Trouble Code (DTC) P1404 sets.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 3 The EGR vacuum vent solenoid is normally closed. When the EGR vacuum vent solenoid is closed, it will vent to atmosphere. Therefore it should not hold vacuum with this test.
2. 4 The EGR valve vacuum control solenoid is normally closed. When vacuum is applied to the commanded open EGR vacuum vent solenoid it should hold vacuum. If the vacuum does not hold, then a stuck open EGR valve vacuum control solenoid is indicated.

The Fuel Injector Control Module (FICM) activates the fuel injector. The Engine Control Module (ECM) signals the FICM to turn ON the injectors through the fuel injector control circuits. The FICM self monitors the supply voltage whenever the ignition is ON. If the FICM senses a low voltage condition, DTC P1550 will set.

The Engine Control Module (ECM) uses the 5-volt reference 1 circuit as a sensor feed to the following sensors

1. The Accelerator Pedal Position (APP) sensor 1.
2. The APP sensor 3.
3. The Fuel Rail Pressure (FRP) sensor.

The ECM monitors the voltage on the 5-volt reference 1 circuit. If the voltage is out of tolerance, the ECM will set DTC P1635.

The numbers below refer to the step number in the diagnostic procedures.

1. 8 A short to the Transmission Control Module (TCM) MIL request may not show up on the scan tool as skewed sensor readings. The TCM momentarily grounds the circuit as a test, and the test is just long enough to set this DTC.
2. 11 This vehicle is equipped with a ECM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the ECM is being replaced, the new ECM must be programmed.

The Engine Control Module (ECM) uses the 5-volt reference 2 circuit as a sensor feed to the following sensors

1. The boost sensor.
2. The Accelerator Pedal Position (APP) sensor 2.
3. The Exhaust Gas Recirculation (EGR) vacuum sensor, if applicable.
4. The Barometric (BARO) pressure sensor.

The ECM monitors the voltage on the 5-volt reference 2 circuit. If the voltage is out of tolerance, the ECM will set DTC P1639.

The numbers below refer to the step number in the diagnostic procedures.

1. 8 If the circuit is shorted to the Transmission Control Module (TCM) MIL request circuit, the scan tool will show skewed BARO and boost sensor readings just after the ignition is turned ON. The sensor readings will then return to normal in under 1 second.
2. 11 This vehicle is equipped with a ECM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the ECM is being replaced, the new ECM must be programmed.

A Wait to Start indicator is illuminated by the Engine Control Module (ECM) when the glow plugs are commanded ON. When the ECM is commanding the Wait To Start indicator ON, the voltage potential of the circuit will be low, near 0 volts. When the ECM is commanding the Wait To Start indicator OFF, the voltage potential of the circuit will be high, near battery voltage. The primary function of the ECM is to supply the ground for the Wait To Start indicator control circuit.

The numbers below refer to the step numbers in the diagnostic procedures.

1. 2 The Wait to Start indicator is illuminated briefly when the ignition is turned ON. The ON time depends upon the temperature of the engine at that time.
2. 5 If the fuse opens during this test, there is a short to voltage on the control circuit.
3. 9 If no trouble is found in the control circuit or the connection at the ECM, the ECM may be malfunctioning.

The Fuel Injection Control Module (FICM) self monitors driver performance and sends this information to the Engine Control Module (ECM) through the CAN system. If a fault is detected in the driver circuits, the FICM will signal the ECM, and DTC P1658 will set. This is an internal circuit fault, and can not be caused by external failures.

The Transmission Control Module (TCM) Malfunction Indicator Lamp (MIL) request circuit signals the Engine Control Module (ECM) that the TCM is requesting MIL illumination.

Diesel engines do not create enough engine vacuum on their own to allow the Exhaust Gas Recirculation (EGR) gases into the combustion process. When the Engine Control Module (ECM) commands the EGR valve to open, the EGR throttle valve will be commanded closed. The EGR throttle valve creates a restriction of incoming fresh air to the engine in order to create engine vacuum. When the EGR throttle valve is closed, engine vacuum develops and allows exhaust gases to enter the engine from the EGR system. The EGR throttle valve vacuum control solenoid is supplied 12 volts by the ignition 1 voltage circuit. The EGR throttle valve vacuum control solenoid is controlled through the EGR throttle valve vacuum solenoid control circuit by the ECM. If the ECM detects a low voltage condition on the EGR throttle valve vacuum solenoid control circuit, DTC P2141 sets.

Diesel engines do not create enough engine vacuum on their own to allow the Exhaust Gas Recirculation (EGR) gases into the combustion process. When the Engine Control Module (ECM) commands the EGR valve to open, the EGR throttle valve will be commanded closed. The EGR throttle valve creates a restriction of incoming fresh air to the engine in order to create engine vacuum. When the EGR throttle valve is closed, engine vacuum develops and allows exhaust gases to enter the engine from the EGR system. The EGR throttle valve vacuum control solenoid is supplied 12 volts by the ignition 1 voltage circuit. The EGR throttle valve vacuum control solenoid is controlled through the EGR throttle valve vacuum solenoid control circuit by the ECM. If the ECM detects a high voltage condition on the EGR throttle valve vacuum solenoid control circuit, DTC P2142 sets.

The Engine Control Module (ECM) uses an Exhaust Gas Recirculation (EGR) vacuum vent solenoid and an EGR valve vacuum control solenoid to control the position of the EGR valve. When the EGR valve is desired to open, the EGR vacuum vent solenoid is commanded open and the EGR valve vacuum control solenoid is commanded open. This will allow vacuum from the vacuum pump to open the EGR valve. When the EGR valve is desired closed, the EGR valve vacuum control solenoid is commanded closed and the EGR vacuum vent solenoid is commanded closed. When the EGR vacuum vent solenoid is commanded closed, the EGR vacuum control system is vented to atmosphere which causes the EGR valve to close very fast. The EGR vacuum vent solenoid is supplied 12 volts by the ignition 1 voltage circuit. The EGR vacuum vent solenoid is controlled through the EGR vacuum vent solenoid control circuit by the ECM. If the ECM detects a low voltage condition on the EGR vacuum vent solenoid control circuit, DTC P2144 sets.

The Engine Control Module (ECM) uses an Exhaust Gas Recirculation (EGR) vacuum vent solenoid and an EGR valve vacuum control solenoid to control the position of the EGR valve. When the EGR valve is desired to open, the EGR vacuum vent solenoid is commanded open and the EGR valve vacuum control solenoid is commanded open. This will allow vacuum from the vacuum pump to open the EGR valve. When the EGR valve is desired closed, the EGR valve vacuum control solenoid is commanded closed and the EGR vacuum vent solenoid is commanded closed. When the EGR vacuum vent solenoid is commanded closed, the EGR vacuum control system is vented to atmosphere which causes the EGR valve to close very fast. The EGR vacuum vent solenoid is supplied 12 volts by the ignition 1 voltage circuit. The EGR vacuum vent solenoid is controlled through the EGR vacuum vent solenoid control circuit by the ECM. If the ECM detects a high voltage condition on the EGR vacuum vent solenoid control circuit, DTC P2145 sets.