Engine Controls - Self Diagnostics - 8.1L: Overview Chevrolet Silverado 1500 HD

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 procedure.

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. 6 This step stores the Powertrain Control Module (PCM) 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 PCM loses during the following conditions: When a diagnostic procedures instructs you to clear the DTCs. When a diagnostic procedure instructs you to disconnect the PCM connectors. When a diagnostic procedure instructs you to replace the PCM. See appropriate REMOVAL & INSTALLATION article.
3. 7 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.
4. 9 If there are other modules with DTCs set, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-158433-S36149293242003092600000) . 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.
5. 11 This step is for areas that have inspection and maintenance testing procedures for emissions testing. Use this step if the testing facility found one or more I/M system status that did not set.

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

1. 3 Lack of communication may be due to a partial malfunction of the class 2 serial data circuit or due to a total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition.
2. 4 Determine if the Powertrain Control Module (PCM) has DTCs set which may affect engine cooling operation.
3. 5 The presence of DTCs which begin with "U" indicate some other module is not communicating. The specified procedure will compile all the available information before tests are performed.

Note. On vehicles that have several control modules connected by serial data circuits, one module is the Power Mode Master (PMM). On vehicles covered in this article, the PMM is the Body Control Module (BCM). The BCM uses 3 signals from the ignition switch. These are the Ignition 0, Ignition 1, and Accessory.

Normal vehicle class 2 communications and module operations will not begin until the system power mode has been identified. Discrete wires from the ignition switch contacts are monitored by the BCM in order to determine the correct power mode. The BCM communicates the system power mode to all class 2 modules on the class 2 serial data line.

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

1. 6 This step tests for battery voltage on the signal circuits that are not required.
2. 7 This step tests for no battery voltage on the required signal circuits.
3. 8 If any ignition switch parameters that should be inactive in the present ignition switch position are active, 2 ignition switch signal circuits may be shorted together.
4. 9 This step eliminates open circuits as the cause of the malfunction.

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 procedure.

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 procedure.

1. 1 Make sure that you perform the Inspection/Maintenance System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2 This step runs the HO2S Heater Tests and initiates the EVAP System Test. Preprogramming the scan tool will reduce the amount of time the oxygen sensor heaters operate while verifying the enable criteria. The engine control module considers the engine to be cold if the following conditions are met: Engine Coolant Temperature (ECT) less than 86°F (30°C). ECT and Intake Air Temperature (IAT) are within 14°F (8°C) of each other at start-up.
3. 3 This step runs the EVAP, AIR and the Oxygen Sensor Tests. The EVAP Test begins once the engine coolant reaches a calibrated temperature. The AIR Test, if equipped, begins shortly after Closed Loop and the indicated speed is achieved. The Oxygen Sensor Tests begin once the engine is at operating temperature, in Closed Loop fuel control, and a calibrated amount of time has elapsed.
4. 4 This step runs the Exhaust Gas Recirculation (EGR) Tests. The EGR Tests are run during a gradual deceleration with a closed throttle. The vehicle speed is required in order to maintain a high, steady MAP signal.
5. 5 This step runs the Catalyst Tests. This test runs during the idle period immediately following a cruise period that meets a minimum calibrated RPM and time period.
6. 6 Perform the individual system test for any of the systems that do not update to YES.
7. 7 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 Inspection/Maintenance readiness diagnostics for the catalyst system. The test may be used to set the I/M System Status indicators to YES. Ensure that the vehicle meets the requirements listed 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 procedure.

1. 1 Make sure that you perform the Inspection/Maintenance System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2 Perform the Catalyst Test during the idle period immediately following the cruise period.
3. 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-158433-S13129313922003092600000) .
4. 4 This step helps identify any unique or unusual criteria required to run the diagnostic test if the universal set procedure does not. This information is located in Conditions for Running DTC.
5. 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 in order to execute the I/M readiness diagnostics for the Evaporative (EVAP) emission system. The test may be used in order to set the I/M System Status indicators to YES. The I/M System Status Display on the scan tool provides an indication of when the control module has completed the required tests. The I/M System Status does not indicate that the tests have passed or failed. When all of the diagnostics for a specific system have run and passed and I/M System Status will update to YES. If a test for a specific system has failed, the I/M System Status will update to YES, indicating a determination was made, even if all of the other tests for that system have not run. Performing a visual inspection prior to running the EVAP test may prevent having to repeat the test. A failed or aborted test will require the vehicle to cool down in order to meet the enable criteria to run another test.

The purpose of this test is to satisfy the enable criteria necessary to execute I/M readiness diagnostics for the Oxygen Sensor (O2S, HO2S) system. The test may be used to set the I/M System Status to YES. Ensure the vehicle meets the requirements listed 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 on the procedure.

1. 1 Make sure that you perform the Inspection/Maintenance System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2 The oxygen sensor tests begin shortly after the indicated speed is achieved. The engine RPM may be too low in overdrive on manual transmission vehicles. If difficulty is encountered updating the status, operate the vehicle in the recommended gear during the test.
3. 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-158433-S04543802602003092600000) .
4. 4 This step helps identify any unique or unusual criteria required to run the diagnostic test if the universal set procedure does not. This information is located in Conditions for Running DTC.
5. 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 diagnostics for the Heated Oxygen Sensor (HO2S) system. The test may be used to set the I/M System Status to YES. Ensure the vehicle meets the requirements listed in Conditions for Running before performing this test. If you do not meet the necessary requirements, test results may be inaccurate.

The numbers below refer to the step numbers on the procedure.

1. 1 Make sure that you perform the I/M System Check before performing this test. If you do not, the I/M System Check may result in difficulty updating the status to YES.
2. 2 Preprogramming the scan tool will reduce the amount of time the oxygen sensor heaters operate while verifying the enable criteria.
3. 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-158433-S39162462792003092600000) .
4. 4 This step helps identify any unique or unusual criteria required to run the diagnostic test if the universal set procedure does not. This information is located in Conditions for Running DTC.
5. 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 diagnostics for the Exhaust Gas Recirculation (EGR) system. The test may be used to set the I/M System Status indicators to YES. Ensure the vehicle meets the requirements listed 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 number in the diagnostic procedure.

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 The EGR Active Tests are run during a gradual deceleration with a closed throttle. The vehicle speed is required in order to maintain a high, steady MAP signal.
3. 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. Refer to «DIAGNOSTIC AIDS»(ref-158433-S03426672182003111800000) .
4. 4 This step helps identify unique or unusual criteria required to run the diagnostic test if the universal set procedure does not run. This information is located in the service information under Conditions for Running the DTC.
5. 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 Mass Air Flow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The Powertrain Control Module (PCM) uses the MAF sensor signal in order to provide the correct fuel delivery for all engine speeds and loads. A small quantity of air entering the engine indicates a deceleration or idle. A large quantity of air entering the engine indicates an acceleration or high load condition. The MAF sensor has an ignition 1 voltage circuit, a ground circuit, and a signal circuit. The PCM applies a voltage to the sensor on the signal circuit. The sensor uses the voltage in order to produce a frequency based on inlet air flow through the sensor bore. The frequency varies within a range of around 2,000 Hertz at idle to about 10,000 Hertz at maximum engine load. The PCM uses the following sensor inputs in order to calculate a predicted MAF value

1. The Manifold Absolute Pressure (MAP).
2. The Intake Air Temperature (IAT).
3. The engine speed (RPM).

The PCM compares the actual MAF sensor frequency signal to the predicted MAF value. This comparison will determine if the signal is stuck based on a lack of variation, or is too low or too high for a given operating condition. DTC P0101 sets if the actual MAF sensor frequency signal is not within a predetermined range of the calculated MAF value.

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

1. 5 This step will determine if the MAP sensor pressure is within the proper range for a given altitude.
2. 6 This step will determine if the MAP sensor voltage is within the proper range at idle.
3. 7 This step will determine if the MAP sensor responds properly to the change in manifold pressure.
4. 8 This step will determine if the TP sensors are operating properly.
5. 9 This step will determine if any mechanical faults have caused this DTC to set.
6. 10 This voltage drop test will determine if high resistance has caused this DTC to set.

Scheme 498

Scheme 499

ALTITUDE VERSUS BAROMETRIC PRESSURE

The Mass Air Flow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The Powertrain Control Module (PCM) uses the MAF sensor signal in order to provide the correct fuel delivery for a wide range of engine speeds and loads. A small quantity of air entering the engine indicates a deceleration or idle. A large quantity of air entering the engine indicates an acceleration or high load condition. The MAF sensor has an ignition 1 voltage circuit, a ground circuit, and a signal circuit. The PCM applies a voltage to the sensor on the signal circuit. The sensor uses the voltage in order to produce a frequency based on inlet air flow through the sensor bore. The frequency varies within a range of around 2,000 Hertz at idle to about 10,000 Hertz at maximum engine load. DTC P0102 sets if the PCM detects a frequency signal lower than the possible range of a properly operating MAF sensor.

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

1. 5 This step will determine if any mechanical faults have caused this DTC to set.
2. 7 This voltage drop test will determine if high resistance has caused this DTC to set.
3. 9 This step verifies the signal circuit from the MAF sensor electrical connector to the PCM.
4. 10 This step tests the signal circuit of the MAF sensor for a short to another 5-volt reference circuit.
5. 11 This step will determine if the PCM is able to process the frequency signal that it receives from the MAF sensor.
6. 14 This step will determine which portion of the circuit or which component is shorted to ground.
7. 17 This step verifies that the signal circuit is not shorted to any other PCM circuit.

Scheme 500

Scheme 501

Scheme 502

The Mass Air Flow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The Powertrain Control Module (PCM) uses the MAF sensor signal in order to provide the correct fuel delivery for a wide range of engine speeds and loads. A small quantity of air entering the engine indicates a deceleration or idle. A large quantity of air entering the engine indicates an acceleration or high load condition. The MAF sensor has an ignition 1 voltage circuit, a ground circuit, and a signal circuit. The PCM applies a voltage to the sensor on the signal circuit. The sensor uses the voltage in order to produce a frequency based on inlet air flow through the sensor bore. The frequency varies within a range of around 2,000 Hertz at idle to about 10,000 Hertz at maximum engine load. DTC P0103 sets if the PCM detects a frequency signal higher than the possible range of a properly operating MAF sensor.

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

1. 3 This step tests for Electromagnetic Interference (EMI) on the signal circuit of the MAF sensor. A frequency reading with the MAF sensor disconnected indicates an EMI related fault or a poor connection at the PCM. Disconnecting the MAF sensor may set additional related DTCs.
2. 4 This step will determine if incorrect harness routing has caused this DTC to set.
3. 5 This step will determine if water intrusion has caused this DTC to set.

Scheme 503

The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in the intake manifold. The pressure changes occur based on the engine load. The MAP sensor has the following circuits

1. 5-volt reference circuit.
2. Low reference circuit.
3. MAP sensor signal circuit.

The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The PCM also provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the MAP sensor signal circuit which is relative to the pressure changes in the manifold. The PCM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. The PCM should detect a high signal voltage at a high MAP, such as the ignition is ON, with the engine OFF, or at a Wide Open Throttle (WOT). The MAP sensor is also used in order to determine the Barometric (BARO) pressure. This occurs when the ignition switch is turned ON, with the engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range.

The PCM calculates a predicted value for the MAP sensor based on throttle position and engine speed. The PCM then compares the predicted value to the actual MAP sensor signal. The DTC P0106 will set if the MAP sensor signal is not within the predicted range.

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

1. 4 This step tests the MAP sensors ability to correctly indicate Barometric (BARO) pressure.
2. 6 This step tests the MAP sensors ability to respond to an increase in engine vacuum.
3. 8 This step tests for a proper MAP sensor pressure with an applied vacuum.

Scheme 504

Scheme 505

Scheme 506

The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in the intake manifold. The pressure changes occur based on the engine load. The MAP sensor has the following circuits

1. 5-volt reference circuit.
2. Low reference circuit.
3. MAP sensor signal circuit.

The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The PCM also provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the MAP sensor signal circuit which is relative to the pressure changes in the intake manifold. The PCM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. The PCM should detect a high signal voltage at a high MAP, such as the ignition is ON, with the engine OFF, or at a Wide Open Throttle (WOT). The MAP sensor is also used in order to determine the Barometric (BARO) pressure. This occurs when the ignition switch is turned ON, with the engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range. If the PCM detects a MAP sensor signal voltage that is excessively low, DTC P0107 will set.

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

1. 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 can help to locate an intermittent condition.

Scheme 507

Scheme 508

The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in the intake manifold. The pressure changes occur based on the engine load. The MAP sensor has the following circuits

1. 5-volt reference circuit.
2. Low reference circuit.
3. MAP sensor signal circuit.

The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The PCM also provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the MAP sensor signal circuit which is relative to the pressure changes in the intake manifold. The PCM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. The PCM should detect a high signal voltage at a high MAP, such as the ignition is ON, with the engine OFF, or at a Wide Open Throttle (WOT). The MAP sensor is also used in order to determine the Barometric (BARO) pressure. This occurs when the ignition switch is turned ON, with the engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range. If the PCM detects a MAP sensor signal voltage that is excessively high, DTC P0108 will set.

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

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

Scheme 509

Scheme 510

The Intake Air Temperature (IAT) sensor is a variable resistor, sometimes called a thermistor. The IAT sensor has a signal circuit and a low reference circuit. The IAT sensor measures the temperature of the air entering the engine. The Powertrain Control Module (PCM) 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 PCM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the IAT signal circuit. If the PCM 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 has a signal circuit and a low reference circuit. The IAT sensor measures the temperature of the air entering the engine. The Powertrain Control Module (PCM) 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 PCM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the IAT signal circuit. If the PCM 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 procedure.

1. 6 This step tests for the proper operating 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.

Scheme 511

Scheme 512

The Engine Coolant Temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The Powertrain Control Module (PCM) supplies 5 volts to the signal circuit and a ground for the ECT low reference circuit. When the ECT is low, the sensor resistance is high. When the ECT is high, the sensor resistance is low. The PCM uses this input for engine controls and enabling criteria for diagnostics. The internal clock of the PCM will record the amount of time the ignition is OFF. At restart the PCM will compare the temperature difference between the ECT and the Intake Air Temperature (IAT). Before failing this test the PCM will perform a calculation to determine the presence of a block heater. If the PCM detects that the temperature difference is not within the calibrated amount after the ignition OFF time, DTC P0116 sets.

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

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. 8 This step tests for a skewed sensor through the range of temperatures affecting this DTC.

Scheme 513

Scheme 514

TEMPERATURE VS. RESISTANCE

The Intake Air Temperature (IAT) sensor is a variable resistor. The IAT sensor has a signal circuit and a low reference circuit. The IAT sensor measures the temperature of the air entering the engine. The Powertrain Control Module (PCM) supplies 5 volts to the IAT signal circuit and a ground for the IAT low reference circuit. When the IAT sensor is cold, the sensor resistance is high. When the air temperature increases, the sensor resistance decreases. With high sensor resistance, the PCM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the IAT signal circuit. If the PCM detects an excessively high IAT signal voltage, indicating a low temperature, DTC P0113 sets.

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

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. 8 This step tests for a skewed sensor through the range of temperatures affecting this DTC.

Scheme 515

Scheme 516

Scheme 517

Scheme 518

The Engine Coolant Temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures the temperature of the engine coolant. The Powertrain Control Module (PCM) 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 PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit. If the PCM detects an excessively low ECT signal voltage, which is a high temperature indication, this Diagnostic Trouble Code (DTC) will set.

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

The Throttle Position (TP) sensor 1 is a potentiometer type sensor with 3 circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A signal circuit.

The TP sensor is used to determine the throttle plate angle for various engine management systems. The control module provides the TP sensor a 5-volt reference circuit and a low reference circuit. The TP sensor then provides the control module a signal voltage proportional to throttle plate movement. TP sensor 1 signal voltage is low at closed throttle and increases as the throttle opens. When the control module detects that the TP sensor 1 signal or TP sensor 5-volt reference voltage is outside the predetermined range, this DTC sets.

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

1. 33 When the TAC module detects a condition within the TAC system, more than one TAC system related DTC may set. This is due to the may redundant tests run continuously on this system. Locating and repairing one individual condition may correct more than one DTC. Disconnecting components during testing may set additional DTCs. Keep this in mind when reviewing the stored information, Capture info.

Scheme 519

Scheme 520

Scheme 521

Scheme 522

The Engine Coolant Temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the Powertrain Control Module (PCM) for engine control, and as an enabling criteria for some diagnostics.

Air flow coming into the engine is accumulated and used to determine if the engine has been driven within conditions that would allow the engine coolant to heat up normally the Closed Loop temperature. If the coolant temperature does not increase normally or does not reach Closed Loop temperature, the diagnostics that use engine coolant temperature as enabling criteria may not run when expected.

This DTC will only run once per ignition cycle within the enabling conditions. If the PCM detects the calibrated amount of air flow and engine run time have been met and the ECT has not met the Closed Loop temperature, DTC P0125 sets.

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

1. 3 This step tests for excessive resistance in the ECT circuit.
2. 7 This step tests for a skewed sensor through the range of temperatures affecting this DTC.

Scheme 523

Scheme 524

The Engine Coolant Temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the Powertrain Control Module (PCM) for engine control, and as an enabling criteria for some diagnostics.

Air flow coming into the engine is accumulated and used to determine if the engine has been driven within conditions that would allow the engine coolant to heat up normally to Closed Loop temperature. If the coolant temperature does not increase normally or does not reach Closed Loop temperature, the diagnostics that use engine coolant temperature as enabling criteria may not run when expected.

This DTC will only run once per ignition cycle within the enabling conditions. If the PCM detects the calibrated amount of air flow and engine run time have been met and the ECT has not met the Closed Loop temperature, DTC P0125 sets.

An Engine Coolant Temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the Powertrain Control Module (PCM) for engine control and as an enabling criteria for some diagnostics. The air flow coming into the engine is accumulated and 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. This Diagnostic Trouble Code (DTC) will only run once per ignition cycle within the enabling conditions. If the engine coolant fails to reach a preset target temperature before a calculated air flow is accumulated, DTC P0128 will set.

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

1. 3 This step tests for excessive resistance in the ECT circuit.
2. 7 This step tests for a skewed sensor through the range of temperatures affecting this DTC.

Scheme 525

An Engine Coolant Temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the Powertrain Control Module (PCM) for engine control and as an enabling criteria for some diagnostics. The air flow coming into the engine is accumulated and 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. This Diagnostic Trouble Code (DTC) will only run once per ignition cycle within the enabling conditions. If the engine coolant fails to reach a preset target temperature before a calculated air flow is accumulated, DTC P0128 will set.

Heated Oxygen Sensor (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The Powertrain Control Module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and closed loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream; low HO2S voltage indicates a lean exhaust stream. If the PCM detects an HO2S voltage that stays below a specified value, DTCs P0131 or P0151 will set.

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

1. 2 If the voltage is varying above and below the specified value the condition is not present.

Scheme 526

Scheme 527

Heated Oxygen Sensor (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The Powertrain Control Module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and closed loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream; low HO2S voltage indicates a lean exhaust stream. If the PCM detects an HO2S voltage that stays below a specified value, DTCs P0131 or P0151 will set.

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

1. 2 If the voltage is above and below the specified value the condition is not present.

Scheme 528

Scheme 529

Scheme 530

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. the Powertrain Control Module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and closed loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream; low HO2S voltage indicates a lean exhaust stream. This diagnostic will only run once per ignition cycle. The PCM monitors the rich-to-lean and lean-to-rich transition time. A transition is defined as, the HO2S voltage changes from above 600 mV to below 250 mV or from below 250 mV to above 600 mV. If the PCM detects that the transition time is too long, DTCs P0133 or P0153 will set.

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

1. 2 If the voltage is varying above and below the specified value, the condition is not present.

Scheme 531

Scheme 532

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content in the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The Powertrain Control Module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and closed loop is achieved, the HO2S generates a voltage within a range of 0-1000 mv that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream; low HO2S voltage indicates a lean exhaust stream. If the PCM detects that the HO2S voltage remains within the bias voltage range, DTCs P0134 or P0154 will set.

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

1. 3 If the HO2S voltage is varying outside the specified range, the condition is not present.

Scheme 533

Scheme 534

The Heated Oxygen Sensor (HO2S) must reach operating temperature to provide an accurate voltage signal. A heating element inside the HO2S minimizes the time required for the sensor to reach operating temperature. Voltage is provided to the heater by the ignition 1 voltage circuit through a fuse. With the engine running, ground is provided to the heater by the HO2S heater low control circuit, through a low side driver within the Powertrain Control Module (PCM). The PCM commands the heater ON or OFF to maintain a specific HO2S operating temperature range. The PCM determines the temperature by measuring the current flow through the heater. When the heater is in the ON state, the PCM will pulse the heater OFF for a duration of 50 ms, once per second. The PCM also monitors the current flow through the heater for diagnosis. This diagnostic will only run once per ignition cycle. If the PCM detects that the current is above or below a specified range, DTC P0135, P0141, P0155 or P0161 sets.

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

1. 7 With no fault present, the test lamp will blink once per second.

Scheme 535

Scheme 536

Heated Oxygen Sensors (O2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The Powertrain Control Module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and closed loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream; low HO2S voltage indicates a lean exhaust stream. If the PCM detects an HO2S voltage that stays below a specified value, DTCs P0137 or P0157 will set.

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

1. 2 If the voltage does not change more than the specified value, the condition is present.

Scheme 537

Scheme 538

Scheme 539

Heated Oxygen Sensors (O2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The Powertrain Control Module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and closed loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream; low HO2S voltage indicates a lean exhaust stream. If the PCM detects an HO2S voltage that stays below a specified value, DTCs P0138 or P0158 will set.

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

1. 2 If the voltage does not change more than the specified value, the condition is present.

Scheme 540

Scheme 541

Scheme 542

Heated Oxygen Sensors (O2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The Powertrain Control Module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and closed loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream; low HO2S voltage indicates a lean exhaust stream. If the PCM detects an HO2S voltage that stays below a specified value, DTCs P0140 or P0160 will set.

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

1. 3 If the voltage is varying above and below the specified value, the condition is not present.

Scheme 543

Scheme 544

The Powertrain Control Module (PCM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during Open and Closed Loop. During Open Loop, the PCM determines fuel delivery based on sensor signals without oxygen sensor (O2S) input. During Closed Loop, the O2S inputs are added and used by the PCM to calculate short and long term fuel trim fuel delivery adjustments. If the O2S indicate a lean condition, fuel trim values will be above 0 percent. If the O2S indicate a rich condition, fuel trim values will be below 0 percent. Short term fuel trim values change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. Long term fuel trim makes coarse adjustment s in order to maintain an air/fuel ratio of 14.7:1. If the PCM detects an excessively lean condition, DTC P0171 or P0174 sets.

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

1. 5 If conditions were not corrected, check fuel system. See «FUEL SYSTEMS»(ref-152876-S21260063022003030100000) in BASIC DIAGNOSTIC PROCEDURES - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL article.
2. 6 If conditions were not corrected, a worn cam, worn intake or exhaust valves, or other engine mechanical failures may be at fault.

Scheme 545

Scheme 546

The Powertrain Control Module (PCM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy and emission control. Fuel delivery is controlled differently during Open and Closed Loop. During Open Loop the PCM determines fuel delivery based on sensor signals, without oxygen sensor input. During Closed Loop, the oxygen sensor inputs are added and used by the PCM to calculate short and long term fuel trim, fuel delivery adjustments. If the oxygen sensors indicate a lean condition, fuel trim values will be above 0 percent. If the oxygen sensors indicate a rich condition, fuel trim values will be below 0 percent. Short term fuel trim values change rapidly in response to the Heated Oxygen Sensor (HO2S) voltage signals. Long term fuel trim makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. The fuel trim diagnostic will conduct a test to determine if a rich failure actually exists or if excessive vapor from the Evaporative (EVAP) emission canister is causing a rich condition. If the PCM detects an excessively rich condition, this Diagnostic Trouble Code (DTC) will set.

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

1. 5 If conditions were not corrected, see «BASIC DIAGNOSTIC PROCEDURES - 8.1L AVALANCHE, SIERRA, SILVERADO, SUBURBAN & YUKON XL»(ref-152876) article.
2. 6 If conditions were not corrected, a worn cam, worn intake or exhaust valves, or other engine mechanical conditions may exist.

Scheme 547

Scheme 548

The control module enables the appropriate fuel injector on the intake stroke for each cylinder. Ignition voltage is supplied to the fuel injectors. The control module controls each fuel injector by grounding the control circuit via a solid state device called a driver. The control module monitors the status of each driver. If the control module detects an incorrect voltage for the commanded state of the driver, a fuel injector control DTC sets.

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

1. 4 This step tests for voltage at the fuel injector harness connector. The INJ fuse supplies power to the coil side of the fuel injector harness connector. If the B+ supply circuit is indicated.
2. 5 This step verifies that the PCM is able to control the fuel injector. If the lamp blinks, then the PCM and wiring are OK.
3. 6 This step tests if a ground is constantly being applied to the fuel injector.

Scheme 549

Scheme 550

The Throttle Position (TP) sensor 2 is a potentiometer type sensor with 3 circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A signal circuit.

The TP sensor is used to determine the throttle plate angle for various engine management systems. The control module provides the TP sensor a 5-volt reference circuit and a low reference circuit. The TP sensor then provides the control module a signal voltage proportional to throttle plate movement. TP sensor 1 signal voltage is low at closed throttle and increases as the throttle opens. When the control module detects that the TP sensor 2 signal or the TP sensor 5-volt reference voltage is outside the predetermined range, this DTC sets.

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

1. 31 When the TAC module detects a condition within the TAC system, more than one TAC system related DTC may set. This is due to the may redundant tests run continuously on this system. Locating and repairing one individual condition may correct more than one DTC. Disconnecting components during testing may set additional DTCs. Keep this in mind when reviewing the stored information, Capture Info.

Scheme 551

Scheme 552

Scheme 553

Scheme 554

The Powertrain Control Module (PCM) provides ignition positive voltage to the coil side of the fuel pump relay. When the ignition switch is first turned ON, the PCM energizes the fuel pump relay, which applies power to the fuel pump. The PCM enables the fuel pump relay as long as the engine is cranking or running, and crankshaft reference pulses are received. If no crankshaft reference pulses are received, the PCM de-energizes the fuel pump relay after 2 seconds. The PCM monitors the voltage on the fuel pump relay control circuit. If the PCM detects an incorrect voltage on the fuel pump relay control circuit, DTC P0230 sets.

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

1. 2 Listen for a click when the fuel pump relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
2. 4 This step verifies that the PCM is providing voltage to the fuel pump relay.
3. 5 This step tests for an open in the ground circuit to the fuel pump relay.
4. 6 This step determines if voltage is constantly being applied to the control circuit of the fuel pump relay.

Scheme 555

Scheme 556

The Powertrain Control Module (PCM) uses information from the crankshaft position (CKP) sensor and the camshaft position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder, the PCM is able to detect individual misfire events. A misfire rate that is high enough can cause three-way catalytic converter damage. The Malfunction Indicator Lamp (MIL) will flash ON and OFF when the conditions for catalytic converter damage are present. If the PCM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC P0300 will set.

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

1. 2 If the CKP variations are not within the learned values, the misfire counters may increment.
2. 3 DTC P0135 or P0155 can be set because of a misfire.

Scheme 557

Scheme 558

Scheme 559

The Crankshaft Position (CKP) system variation learn feature is used to calculate reference period errors caused by slight tolerance variations in the crankshaft, and the CKP sensors. The calculated error allows the Powertrain Control Module (PCM) to accurately compensate for reference period variation. This enhances the ability of the PCM to detect misfire events over a wider range of engine speed and load. The PCM stores the CKP system variation values after a learn procedure has been performed. This DTC set indicated that the CKP system variation values have not been stored in the PCM and the CKP system variation learn procedure must be performed.

The Knock Sensor (KS) produce an AC signal when specific frequencies are detected. When the engine operates, the Powertrain Control Module (PCM) learns a minimum and maximum frequency of noise of normal engine operation. The KS system monitors both KS in order to determine if knock is present. If the KS system determines that excessive knock is present, the PCM retards the spark timing based on the signals from the KS system. The PCM then retards timing until no knock is present.

The Knock Sensors (KS) produce and AC signal when specific frequencies are detected. When the engine operates, the Powertrain Control Module (PCM) learns a minimum and maximum frequency of noise of normal engine operation. The KS system monitors both knock sensors in order to determine if knock is present. If the KS system determines that excessive knock is present, the PCM retards the spark timing based on the signals from the KS system. The PCM then retards the timing until no knock is present. When the PCM detects a frequency that is less than or more than a defined range, DTC P0327 will sent for a failure in KS 1 which is located on bank 1 on the drivers side of the engine or DTC P0332 will set for a failure in KS 2 which is located on bank 2 on the passenger side of the engine.

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

1. 2 This step ensures the malfunction is present.
2. 3 This test will isolate the KS from the rest of the circuit.
3. 4 Tapping on the engine block will simulate an engine knock.

Scheme 560

Scheme 561

The crankshaft position (CKP) sensor signal indicates the crankshaft speed and position. The CKP sensor is connected directly to the Powertrain Control Module (PCM), and consists of the following circuits

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

If the PCM detects there is no signal from the CKP sensor for 3 seconds, DTC P0335 sets.

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

1. 3 This step determines if the fault is present.
2. 6 This step simulates a CKP sensor signal to the PCM. If the PCM receives the signal, the fuel pump will operate for about 2 seconds.

Scheme 562

Scheme 563

The crankshaft position (CKP) sensor signal indicates the crankshaft speed and position. The CKP sensor is connected directly to the Powertrain Control Module (PCM), and consists of the following circuits

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

If the PCM detects that the CKP sensor signal is inconsistent for 120 seconds, DTC P0336 sets.

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

1. 2 This step verifies that the malfunction is present.
2. 3 This step inspects for electromagnetic interference (EMI) on the CKP sensor circuits.

Scheme 564

Scheme 565

The camshaft position (CMP) sensor works in conjunction with a 1 X reluctor wheel on the camshaft. The Powertrain Control Module (PCM) provides a 12-volt reference to the CMP sensor as well as a low reference and a signal circuit.

As the camshaft rotates, the reluctor wheel interrupts a magnetic field produced by a magnet within the sensor. The sensors internal circuitry detects this and produces a signal which the PCM reads.

The CMP uses this 1 X signal is used by the PCM to determine if the cylinder is at Top Dead Center (TDC) is on the firing stroke or the exhaust stroke. The PCM can determine TDC for all cylinders by using the CKP sensor 24 X signal alone. The engine will start without a CMP signal as long as the PCM receives the CKP sensor 24 X signal. A slightly longer cranking time may be a symptom of this condition. The system attempts synchronization and looks for an increase in engine speed indicating that the engine started. If the PCM does not detect an increase in engine speed, the PCM assumes that the PCM incorrectly synchronized to the exhaust stroke and re-syncs to the opposite cam position. If the PCM detects that a CMP to CKP mis-match has occurred DTC P0341 sets.

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

1. 3 This step inspects for electromagnetic interference (EMI) on the CMP sensor circuits.
2. 6 Damage to the face of the sensor could indicate foreign material passing between the CMP sensor and the reluctor wheel. This condition would cause this DTC to set. Damage to the reluctor wheel would affect the CMP sensor output.

Scheme 566

The camshaft position (CMP) sensor works in conjunction with a 1 X reluctor wheel on the camshaft. The Powertrain Control Module (PCM) provides a 12 volt reference to the CMP sensor as well as a low reference and a signal circuit.

As the camshaft rotates, the reluctor wheel interrupts a magnetic field produced by a magnet within the sensor. The sensors internal circuitry detects this and produces a signal which the PCM reads.

The CMP sensor 1 X signal is used by the PCM to determine if the cylinder at Top Dead Center (TDC) is on the firing stroke or the exhaust stroke. The PCM can determine TDC for all cylinders by using the CKP sensor 24 X signal alone. The engine will start without a CMP signal as long as the PCM receives the CKP sensor 24 X signal. A slightly longer cranking time may be a symptom of this condition. The system attempts synchronization and looks for an increase in engine speed indicating that the engine started. If the PCM does not detect an increase in engine speed, the PCM assumes that the PCM incorrectly synchronized to the exhaust stroke and re-syncs to the opposite cam position. If the PCM detects that a CMP signal is constantly low, DTC P0342 sets.

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

1. 5 This step tests the CMP sensor signal circuit. Applying a voltage causes the CMP sensor high to low and low to high parameter to increase if the circuit and the PCM are operating properly.

Scheme 567

Scheme 568

The camshaft position (CMP) sensor works in conjunction with a 1 X reluctor wheel on the camshaft. The Powertrain Control Module (PCM) provides a 12-volt reference to the CMP sensor as well as a low reference and a signal circuit.

The CMP sensor determines whether a cylinder is on a firing stroke or on an exhaust stroke. As the camshaft rotates, the reluctor wheel interrupts a magnetic field produced by a magnet within the sensor. The sensors internal circuitry detects this and produces a signal which the PCM reads.

The CMP sensor 1 X signal is used by the PCM to determine if the cylinder at Top Dead Center (TDC) is on the firing stroke or the exhaust stroke. The PCM can determine TDC for all cylinders by using the CKP sensor 24 X signal. A slightly longer cranking time may be a symptom of this condition. The system attempts synchronization and looks for an increase in engine speed indicating that the engine started. If the PCM does not detect an increase in engine speed, the PCM assumes that the PCM incorrectly synchronized to the exhaust stroke and re-syncs to the opposite cam position. If the PCM detects that the CMP signal is constantly high, DTC P0343 sets.

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

1. 5 This step tests the CMP sensor signal circuit. Applying a voltage causes the CMP sensor high to low and low to high parameter to increase if the circuit and the PCM are operating properly.

Scheme 569

Scheme 570

The ignition system on this engine uses an individual ignition coil for each cylinder. The Powertrain Control Module (PCM) controls the ignition system operation. The PCM controls each coil using one of 8 Ignition Control (IC) circuits. The PCM commands the IC circuit low when a spark event is requested. This causes the IC module to energize the ignition coil to create a spark at the spark plug. Each ignition coil has the following circuits

1. The Ignition Control (IC) circuit.
2. The ignition 1 voltage circuit.
3. A ground circuit.
4. A reference low circuit.

The sequencing and timing are PCM controlled. This DTC sets when the IC circuit is out of range.

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

1. 3 This step verifies the integrity of the IC circuit and the PCM output.
2. 4 This step tests for a short to ground on the IC circuit.

Scheme 571

Scheme 572

The Powertrain Control Module (PCM) tests the Exhaust Gas Recirculation (EGR) system during deceleration. The PCM does this by momentarily commanding the EGR valve to open while monitoring the signal circuit of the Manifold Absolute Pressure (MAP) sensor. When the EGR valve is opened, the PCM will expect to see a predetermined increase in MAP. If the expected increase in MAP is not detected, the PCM records the amount of MAP difference that was detected and adjusts a calibrated fail counter towards a calibrated fail threshold level. The number of EGR flow test counts required to exceed the fail threshold may vary according to the amount of detected EGR flow error.

Normally, the PCM will only allow one EGR flow test during an ignition cycle. TO aid in verifying a repair, the PCM will allow up to 13 EGR flow test counts during the first ignition cycle following a code clear event. Between 8-13 EGR flow test counts should be sufficient for the PCM to determine adequate EGR flow and pass the EGR flow test. If the PCM detects an EGR flow error, DTC P0401 sets.

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

1. 2 MAP sensor faults must be diagnosed first. A skewed MAP sensor reading could cause this DTC to set.

Scheme 573

The Powertrain Control Module (PCM) monitors the EGR position sensor parameter of the Exhaust Gas Recirculation (EGR) valve to ensure that the valve responds properly to commands from the PCM. The PCM compares the EGR position sensor parameter with the desired EGR position parameter when the valve is commanded open. If the PCM detects a difference of 12 percent between the EGR position sensor parameter and desired EGR position parameter for a calibrated amount of time, DTC P0404 will set.

The Exhaust Gas Recirculation (EGR) valve position sensor is monitored by the Powertrain Control Module (PCM). The 5-volt reference circuit, low reference circuit and the EGR valve position signal circuit are used by the PCM to determine the EGR valve position. If the EGR valve position sensor signal voltage is pulled below a calibrated value, DTC P0405 sets.

The engine systems uses a 3-way catalytic converter (TWC) to control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides Of Nitrogen (NOx). The catalyst within the TWC promotes a chemical reaction, which oxidizes the HC and CO that are present in the exhaust system. This reaction converts these chemicals into harmless water vapor and carbon dioxide. The catalyst also reduces the NOx which converts into nitrogen. The Powertrain Control Module (PCM) monitors this process using Heated Oxygen Sensors (HO2S) bank 1 sensor 2 and HO2S bank 2 sensor 2, which are located in the exhaust stream past the TWC. These sensors are referred to as catalyst monitor sensors. The catalyst monitor sensors produce an output signal which indicates the oxygen storage capacity of the catalyst. This determines the catalysts ability to effectively convert the exhaust emissions. If the catalyst is functioning correctly, the catalyst monitor signals will be far less active than that of the signals which are produced by the fuel control HO2S 1 bank 1 and fuel control HO2S bank 2. This indicates that the TWC oxygen storage capacity is at an acceptable threshold. When the response time of the catalyst monitors are close to that of the fuel control sensors, the ability of the catalyst to store oxygen is considered to be below an acceptable threshold. If the PCM detects this condition, DTC P0420 catalyst low efficiency for bank 1 or DTC P0430 catalyst low efficiency for bank 2 sets.

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

1. 6 This step inspects for conditions than can cause the 3-way catalytic converter efficiency to appear degraded.
2. 8 A catalytic converter which has been discolored may be due to an engine running rich, lean or had a previous severe misfire. Verifying the fuel trim percentages may be of assistance in determining if such a condition exists.

Scheme 574

Scheme 575

This diagnostic tests the Evaporative Emission (EVAP) system for a small leak when the key is turned OFF and the correct conditions are met.

Heat is transferred into a vehicle fuel tank while the vehicle is operating. When the vehicle is turned OFF, a change in the fuel tank vapor temperature occurs, which may result in corresponding pressure changes in the fuel vapor space. This change is monitored by the control module using the fuel tank pressure sensor input. The control module then makes a judgement on the integrity of the system. With a 0.020 inch (0.51 mm) leak in the system, the amount of pressure change observed is significantly less than that of a sealed system.

If the control module detects a pressure change less than a calibrated amount, DTC P0442 sets.

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

1. 3 Introducing smoke in 15 second intervals may allow smaller leak areas to be more noticeable. When the system is less pressurized, the smoke will sometimes escape in a more condensed manner.
2. 5 This step verifies that repairs are complete and that no other condition is present.

Scheme 576

Scheme 577

An ignition voltage is supplied directly to the Evaporative (EVAP) emission canister purge valve. The EVAP canister purge valve is pulse width modulated (PWM). The scan tool displays the amount of ON time as a percentage. The control module monitors the status of the driver. The control module controls the EVAP canister purge valve ON time by grounding the control circuit via an internal switch called a driver. If the control module detects an incorrect voltage for the commanded state of the driver, this DTC sets.

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

1. 2 This step tests if the concern is active. The EVAP purge valve is PWM. You should hear a clicking sound when the purge valve is commanded to 50 percent. The clicking sound should stop when the EVAP purge valve is commanded to 0 percent. The rate at which the valve cycles should increase when the commanded state is increased, and decrease when the commanded state is decreased. Repeat the commands as necessary.
2. 5 This step verifies that the control module is providing ground to the EVAP purge valve.
3. 6 This step tests if a ground is constantly being applied to the EVAP purge valve.

Scheme 578

Scheme 579

This DTC tests the Evaporative Emission (EVAP) system for a restricted or blocked EVAP vent path. The control module commands the EVAP canister purge solenoid ON and the EVAP canister vent solenoid ON. This allows vacuum to be applied to the EVAP system. Once a calibrated vacuum level has been reached, the control module commands the EVAP canister purge solenoid OFF and the EVAP canister vent solenoid OFF. The control module monitors the Fuel Tank Pressure (FTP) sensor for a decrease in vacuum. If the vacuum does not decrease to near 0 inches H2O in a calibrated time, this DTC sets.

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

1. 3 This test determines if the failure is present or intermittent.

Scheme 580

Scheme 581

An ignition voltage is supplied to the Evaporative Emission (EVAP) canister vent valve. The control module grounds the EVAP canister vent valve control circuit to close the valve be means of an internal switch called a driver. The scan tool displays the commended state of the EVAP canister vent valve as ON or OFF. The control module monitors the status of the driver. If the control module detects an incorrect voltage for the commanded state of the driver, this DTC sets.

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

1. 2 A click should be heard or felt when the valve operates. Ensure that both the ON and the OFF states are commanded. Repeat the commands as necessary.
2. 5 This step verifies that the control module is providing ground to the EVAP vent valve.
3. 6 This step tests if the EVAP vent valve control circuit is grounded.

Scheme 582

Scheme 583

The Fuel Tank Pressure (FTP) sensor measures the difference between the air pressure or vacuum in the evaporative emission (EVAP) system, and the outside pressure. The control module supplies a 5-volt reference and a low reference circuit to the FTP sensor. The FTP sensor signal circuit voltage varies depending on EVAP system pressure or vacuum. If the FTP sensor signal voltage goes below a calibrated value, this DTC sets.

If FTP sensor signal voltage is 1.5 volts or more the FTP has negative pressure/vacuum. If the FTP sensor signal voltage is 1.5 volts or less the FTP has positive pressure.

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

1. 5 This step tests for the proper operation of the circuit in the high voltage range.
2. 6 The 5-volt reference circuit for the FTP sensor is routed through connector C152. This area may provide a good test point for diagnosing concerns with this circuit.
3. 7 The FTP sensor signal circuit is routed through connector C152. This area may provide a good test point for diagnosing concerns with this circuit.

Scheme 584

Scheme 585

The Fuel Tank Pressure measures the difference between the air pressure or vacuum in the Evaporative Emission (EVAP) system, and the outside air pressure. The control module supplies a 5-volt reference and a low reference circuit to the FTP sensor. The FTP sensor signal circuit voltage varies depending on EVAP system pressure or vacuum. If the FTP sensor signal voltage increases above a calibrated value, this DTC sets.

If FTP sensor signal voltage is 1.5 volts or more the FTP has negative pressure/vacuum. If the FTP sensor signal voltage is 1.5 volts or less the FTP has positive pressure.

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

1. 2 If DTC P0641 or P0651 is set, the 5-volt reference circuit maybe shorted to a voltage.

Scheme 586

Scheme 587

The control module tests the Evaporative Emission (EVAP) system for a large leak. The control module monitors the fuel tank pressure (FTP) sensor signal to determine the EVAP system vacuum level. When the conditions for running are met, the control module commands the EVAP canister purge valve OPEN and the EVAP vent valve CLOSED. This allows engine vacuum to enter the EVAP system. At a calibrated time, or vacuum level, the control module commands the EVAP canister purge valve closed, sealing the system, and monitors the FTP sensor input in order to determine the EVAP system vacuum level. If the system is unable to achieve the calibrated vacuum level, or the vacuum level decreases too rapidly, this DTC sets.

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

1. 3 Introducing smoke in 15 second intervals may allow smaller leak areas to be more noticeable. When the system is less pressurized, the smoke will sometimes escape in a more condensed manner.
2. 5 This step verifies proper operation of the Fuel Tank Pressure (FTP) sensor.
3. 6 A normal operating FTP sensor should increase above 5 inches of H2O and stop between 6 and 7 inches of H2O.

Scheme 588

Scheme 589

Scheme 590

This DTC tests for undesired intake manifold vacuum flow to the Evaporative Emission (EVAP) system. The control module seals the EVAP system by commanding the EVAP canister purge valve OFF and the EVAP canister vent valve ON. The control module monitors the Fuel Tank Pressure (FTP) sensor to determine if a vacuum is being drawn on the EVAP system. If vacuum in the EVAP system is more than a predetermined time, this DTC sets.

If the control module command is ON the EVAP purge valve is OPEN and the EVAP canister vent valve is CLOSED. If the control module command is OFF the EVAP purge valve is CLOSED and the EVAP canister vent valve is OPEN.

The Throttle Actuator Control (TAC) system uses vehicle electronics and components to calculate and control the position of the throttle plate. In order to decrease idle speed the TAC system closes the throttle plate reducing airflow into the engine. In order to increase idle speed the TAC system opens the throttle plate allowing more airflow into the engine. If the actual idle RPM does not match the desired idle RPM within a calibrated time, this DTC set.

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

1. 2 This test determines if the engine can achieve the commanded RPM. If the engine does not reach the commanded RPM, the test determines whether the RPM is too high or too low.

Scheme 591

This diagnostic applies to internal microprocessor integrity conditions within the Powertrain Control Module (PCM). This diagnostic also addresses if the PCM is not programmed.

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

1. 2 A DTC P0602 indicates the PCM is not programmed.

Scheme 592

The Powertrain Control Module (PCM) provides 5 volts to the following sensors

1. The Engine Oil Pressure (EOP) sensor.
2. The Exhaust Gas Recirculation (EGR) valve.
3. The Manifold Absolute Pressure (MAP) sensor.

These 5-volt reference circuits are independent of each other outside the PCM, but are bussed together inside the PCM. Therefore a circuit condition on one sensor 5-volt reference circuit may affect the other sensor 5-volt reference circuits. The PCM monitors the voltage on the 5-volt reference circuit. If the PCM detects that the voltage is out of tolerance, DTC P0641 sets.

The Malfunction Indicator Lamp (MIL) is located on the Instrument Panel Cluster (IPC). The MIL informs the driver than an emission system fault has occurred and that the engine control system requires service. The control module monitors the MIL control circuit for conditions that are incorrect for the commanded state of the MIL. For example, a failure condition exists if the control module detects low voltage when the MIL is commanded OFF, or high voltage when the MIL is commanded ON. If the control module detects an improper voltage on the MIL control circuit, DTC P0650 will set.

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

1. 4 This step tests for a short to ground in the MIL control circuit. With the Powertrain Control Module (PCM) disconnected and the ignition ON, the MIL should be OFF.
2. 5 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.

Scheme 593

Scheme 594

The Powertrain Control Module (PCM) provides 5 volts to the following sensors

1. The Air Conditioning (A/C) pressure sensor.
2. The Fuel Tank Pressure (FTP) sensor, if equipped.

These 5-volt reference circuits are independent of each other outside the PCM, but are bussed together inside the PCM. Therefore a circuit condition on one sensor 5-volt reference circuit may affect the other sensor 5-volt reference circuits. The PCM monitors the voltage on the 5-volt reference circuit. The PCM detects that the voltage is out of tolerance, DTC P0651 sets.

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

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

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

Scheme 595

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

The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in the intake manifold. The pressure changes occur based on changes in the intake manifold. The pressure changes occur based on the engine load. The MAP sensor has the following circuits

1. 5-volt circuit.
2. Low reference circuit.
3. MAP sensor signal circuit.

The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The PCM also provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the MAP sensor signal circuit which is relative to the pressure changes in the manifold. The PCM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. The PCM should detect a high signal voltage at a high MAP, such as the ignition is ON, with the engine OFF, or at a Wide Open Throttle (WOT). The MAP sensor is also used in order to determine the Barometric Pressure (BARO). This occurs when the ignition switch is turned ON, with the engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range. If the PCM detects a MAP sensor signal voltage that is intermittently high, DTC P1106 sets.

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

1. 3 This step attempts to pinpoint the location of the intermittent fault.

Scheme 596

The Manifold Absolute Pressure (MAP) sensor responds to pressure changes in the intake manifold. The pressure changes occur based on the engine load. The MAP sensor has the following circuits

1. 5-volt reference circuit.
2. Low reference circuit.
3. MAP sensor signal circuit.

The Powertrain Control Module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The PCM also provides a ground on the low reference circuit. The MAP sensor provides a signal to the PCM on the MAP sensor signal circuit which is relative to the pressure changes in the manifold. The PCM should detect a low signal voltage at a low MAP, such as during an idle or a deceleration. The PCM should detect a high signal voltage at a high MAP, such as the ignition is ON, with the engine OFF, or at a Wide Open Throttle (WOT). The MAP sensor is also used in order to determine the Barometric Pressure (BARO). This occurs when the ignition switch is turned ON, with the engine OFF. The BARO reading may also be updated whenever the engine is operated at WOT. The PCM monitors the MAP sensor signal for voltage outside of the normal range. If the PCM detects a MAP sensor signal voltage that is intermittently low, DTC P1107 sets.

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

1. 3 This step attempts to pinpoint the location of the intermittent t fault.

Scheme 597

The Intake Air Temperature (IAT) sensor is a variable resistor, sometimes called a thermistor. The IAT sensor has a signal circuit and a low reference circuit. The IAT sensor measures the temperature of the air entering the engine. The Powertrain Control Module (PCM) 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 PCM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the IAT signal circuit. If the PCM detects an intermittent high IAT signal voltage, indicating a low temperature, DTC P1111 sets.

The Intake Air Temperature (IAT) sensor is a variable resistor, sometimes called a thermistor. The IAT sensor has a signal circuit and a low reference circuit. The IAT sensor measures the temperature of the air entering the engine. The Powertrain Control Module (PCM) 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 PCM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the IAT signal circuit. If the PCM detects an intermittent low IAT signal voltage, indicating a high temperature, DTC P1112 sets.

The Engine Coolant Temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures the temperature of the engine coolant. The Powertrain Control Module (PCM) 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 PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit. If the PCM detects an excessively low ECT signal voltage, which is a high temperature indication, this Diagnostic Trouble Code (DTC) will set.

The Engine Coolant Temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures the temperature of the engine coolant. The Powertrain Control Module (PCM) 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 PCM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT signal circuit, if the PCM detects an excessively high signal voltage, which is a low temperature indication, this Diagnostic Trouble Code (DTC) will set.

The Accelerator Pedal Position (APP) sensor is mounted on the accelerator pedal assembly. The sensor is actually 2 individual APP sensors within 1 housing. Two separate signal circuits are used in order to connect the accelerator pedal sensor assembly, and the Throttle Actuator Control (TAC) module

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A signal circuit.

If only 1 APP sensor DTC is set, the redundant APP systems allow the TAC system to continue operating normally. This DTC sets if the Powertrain Control Module (PCM) detects a condition with more than 1 APP sensor. One APP sensor DTC will not cause the Reduced Engine Power message to be displayed. 2 APP sensor DTCs for the same sensor also will not cause the Reduced Engine Power message to be displayed. However, if two or more DTCs are set involving more than 1 APP sensor, this DTC will set and the Reduced Engine Power message is displayed.

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

1. 2 When the problems are corrected which are causing the APP sensor DTCs to set, the status of this DTC will change to history.

Scheme 598

Heated Oxygen Sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compared the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The Powertrain Control Module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and closed loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream; low HO2S voltage indicates a lean exhaust stream. This diagnostic will only run once per ignition cycle. The PCM monitors the number or rich-to-lean and lean-to-rich transitions. A transition is defined as, the HO2S voltage changes from above 600 mV to below 250 mV or from below 250 mV to above 600 mV. If the PCM detects that the number or transitions were less than a specified value, DTCs P1133 or P1153 will set.

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

1. 2 If the voltage is varying above and below the specified value, the condition is not present.

Scheme 599

Scheme 600

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. The Diagnostic Trouble Code (DTC) sets when the Powertrain Control Module (PCM) 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 procedure.

1. 2 This step tests the supply voltage circuit of the secondary fuel pump relay.
2. 4 This step verifies the secondary fuel pump operation. Listen for an audible sound as the secondary fuel pump relay harness connector is jumpered.
3. 5 This step verifies that there is adequate fuel in the rear fuel tank. The rear fuel tank sensor voltage must be above 1 volt in order to continue.
4. 7 This step tests the secondary fuel pumps ability to transfer fuel. The rear fuel level sensor voltage should decrease while the secondary fuel pump is ON.
5. 8 This step tests for a short to ground on the control circuit of the secondary fuel pump relay. If the test lamp illuminates, a short to ground is indicated.
6. 9 This step tests for a short to voltage on the control circuit of the secondary fuel pump relay. If the test lamp illuminates, a short to voltage is indicated.
7. 10 This step verifies the secondary fuel pump relay operation. An audible click should be heard as the secondary fuel pump relay control circuit is grounded. The secondary fuel pump should turn ON as the fuel pump relay control circuit is grounded.

Scheme 601

Scheme 602

Scheme 603

Scheme 604

The PCM uses the ECT sensor to monitor the engine for an over temperature condition. This condition occurs when the coolant temperature is above 270°F (132°C). When an over temperature condition is present, DTC P1258 will set. The PCM will disable two groups of four cylinders by turning OFF the fuel injectors. By switching between the two groups of cylinders, the PCM is able to reduce the temperature of the coolant.

The Powertrain Control Module (PCM) detects engine misfire events by monitoring variations in crankshaft rotation speed. Wheel speed changes caused by rough road conditions can cause changes in crankshaft speed. By monitoring the wheel speed sensors, the Anti-Lock Brake System (ABS) can determine if the vehicle is operating on a rough road. If the ABS is detecting a rough road condition severe enough to effect misfire detection, a rough road signal is sent to the PCM on the serial data circuit. If DTC P0300 is set and the rough road information is not available due to an ABS malfunction, DTC P1380 will set.

The Powertrain Control Module (PCM) detects engine misfire events by monitoring variations in the crankshaft rotation speed. Wheel speed changes caused by rough road conditions can cause changes in crankshaft speed. By monitoring the wheel speed sensors, the Anti-Lock Brake System (ABS) can determine if the vehicle is operating on a rough road. If the ABS is detecting a rough road condition severe enough to effect misfire detection, a rough road signal is sent to the PCM on the serial data circuit. If DTC P0300 is set and the rough road information is not available due to and ABS malfunction, DTC P1381 will set.

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

1. 1 This step will diagnose a malfunction in the serial data circuits.

Scheme 605

The Powertrain Control Module (PCM) monitors the Exhaust Gas Recirculation (EGR) valve pintle position input to ensure that the valve responds properly to commands from the PCM. When the ignition switch is turned ON, the PCM learns the EGR learned minimum position. The PCM compares the EGR learned minimum position to the EGR position sensor when the EGR valve is commanded closed. If the EGR position sensor indicates that the EGR valve is still open when the PCM is commanding the EGR valve closed, this DTC will set.

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

1. 2 This step verifies that the malfunction is present.

Scheme 606

Scheme 607

The Powertrain Control Module (PCM) uses the following readings in order to calculate the predicted Mass Air Flow (MAF) rate

1. The Throttle Position (TP).
2. The Barometric (BARO) pressure.
3. The Intake Air Temperature (IAT).
4. The engine RPM.

The PCM compares the predicted MAF value to the actual MAF value, and to the speed density calculation in order to verify the proper throttle operation.

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

1. 5 Locating and repairing an individual condition may correct more than 1 DTC.

Scheme 608

The commanded Throttle Position (TP), based on Accelerator Pedal Position (APP) and possibly other limiting factors, is compared to the actual TP. The 2 values should be within a calibrated range of each other. Both the Powertrain Control Module (PCM) and the Throttle Actuator Control (TAC) module redundantly monitor the commanded and actual TP. This DTC sets if the PCM detects an out-of-range condition between commanded and actual pedal position.

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

1. 5 If the TP indicated angle does not follow the movement of the throttle blade, and no TP sensor DTCs are set, there is a mechanical condition with the throttle shaft or the TP sensor.
2. 16 Locating and repairing an individual condition may correct more than 1 DTC.

Scheme 609

Scheme 610

The predicted Throttle Position (TP), based on Accelerator Pedal Position (APP) and other limiting factors, is compared to the Actual throttle position. The 2 values should be within a calibrated range of each other. Both the Powertrain Control Module (PCM) and the Throttle Actuator Control (TAC) module redundantly monitor the predicted and actual throttle position. This DTC sets if the PCM detects an out of range condition between the predicted and actual throttle position.

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

1. 7 If the TP indicated angle does not follow the movement of the throttle blade, and no TP sensor DTCs are set, there is a mechanical condition with the throttle shaft or the TP sensor.
2. 18 Locating and repairing an individual condition may correct more than 1 DTC.

Scheme 611

Scheme 612

The Throttle Actuator Control (TAC) module and the Powertrain Control Module (PCM) communicate via a dedicated serial data circuit. This serial data circuit is separate from any other serial data circuit on the vehicle. Accurate transmitting and receiving of serial data requires not only good circuit integrity but also adequate system voltage. This diagnostic test monitors the accuracy of the serial data transmitted between the TAC module and the PCM. If the PCM detects a loss of data or invalid data, this DTC sets.

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

1. 2 This step determines if the IGN relay is supplying a voltage to the ETC fuse.
2. 5 Increasing the engine speed to 3000 RPM aids in locating a shorted throttle actuator motor control circuit. Depending on the polarity of the throttle actuator motor transistors, this DTC may not set with a fault in the control circuits. The throttle actuator motor is a bi-directional DC motor. Raising the engine speed changes the polarity of the transistors in the throttle actuator motor. This occurs because 1 set of the transistors are low, 0 volts, and the other set are high, battery voltage. Therefore, if 1 set of transistors are at a low voltage and the corresponding circuit is shorted low, DTC P1518 will not set. When the polarity of the transistors change this DTC sets. If this DTC does not Fail This ignition, continue to monitor this DTC status while moving related harnesses and connectors.
3. 29 Locating and repairing an individual condition may correct more than 1 DTC.

Scheme 613

Scheme 614

Scheme 615

Scheme 616

The Throttle Actuator Control (TAC) module contains data which is essential for proper TAC system operation. The TAC module continuously tests the integrity of this data. When the TAC module is unable to write or read data to and from random access memory (RAM), or the TAC module is unable to correctly read data from the flash memory or and internal TAC module processor fault is detected, this DTC sets.

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

1. 4 Locating and repairing an individual condition may correct more than 1 DTC.

Scheme 617

The Accelerator Pedal Position (APP) sensor 1 is a potentiometer type sensor with the following 3 circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A signal circuit.

The control module provides the APP sensor a 5-volt reference circuit and a low reference circuit. The APP sensor then provides the control module a signal voltage proportional to pedal movement. The APP sensor 1 signal voltage is low at rest and increases as the pedal is depressed. When the control module detects that the APP sensor 1 signal or APP sensor 5-volt reference voltage is outside the predetermined range, this DTC sets.

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

1. 12 This test isolates whether the short is to another TAC system circuit in the harness or within the TAC module.
2. 26 When the TAC module detects a condition within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting components during testing may set additional DTCs. Remember this if you review the stored information in Capture Info.

Scheme 618

Scheme 619

Scheme 620

The Accelerator Pedal Position (APP) sensor 1 is a potentiometer type sensor with the following 3 circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A signal circuit.

The control module provides the APP sensor a 5-volt reference circuit and a low reference circuit. The APP sensor then provides the control module a signal voltage proportional to pedal movement. The APP sensor 1 signal voltage is low at rest and increases as the pedal is depressed. The APP sensor 2 signal voltage is also low at rest and increases as the pedal is depressed. When the control module detects that the APP sensor 1 signal and the APP sensor 2 signal circuits are out of correlation, this DTC sets.

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

1. 2 This step determines if a communication condition exists.
2. 5 This step isolates an internal APP sensor failure. The condition may only occur at a certain accelerator pedal position. Monitoring the APP angles for sensor 2 and sensor 3 is an accurate way of verifying the actual position of the pedal. The APP angles for all 3 sensors should be within a set percent of each other. If the pedal is at rest, the APP angle for all 3 sensors should be 0 percent. If the pedal is fully depressed, all APP angles should be 100 percent.
3. 6 The APP sensor 1 shares a common 5-volt reference circuit with the throttle position (TP) sensor 1. Monitoring the TP sensor 1 voltage aids in diagnosing the APP sensor 5-volt reference and low reference circuits. If the scan tool displays near 0 volts, the circuits are OK.
4. 9 With the TAC module still connected, this test will help determine a short to the signal circuit either within the TAC module or wiring.
5. 10 This step determines whether the TAC module or a short circuit is causing the condition.
6. 19 When the TAC module detects a condition within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting components during testing may set addition DTCs. Remember this if you review the stored information in Capture Info.

Scheme 621

Scheme 622

Scheme 623

The Accelerator Pedal Position (APP) sensor 2 is a potentiometer type sensor with the following 3 circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A signal circuit.

The control module provides the APP sensor a 5-volt reference circuit and a low reference circuit. The APP sensor then provides the control module a signal voltage proportional to pedal movement. The APP sensor 1 signal voltage is low at rest and increases as the pedal is depressed. When the control module detects that the APP sensor 2 signal or the APP sensor 5-volt reference voltage is outside the predetermined range, this DTC sets.

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

1. 2 The throttle position (TP) senor 2 and the APP sensor 2 share a common 5-volt reference source. Diagnose DTC P0220 first if P0220 is also set.
2. 18 This test determines whether or not the TAC module can recognize a change in signal voltage.
3. 19 There are 2 separate 5-volt reference sources within the TAC module. The TP sensor 1 and APP sensor 1 share one 5-volt reference source. The TP sensor 2 and the APP sensor 2 share another common 5-volt reference source. The test determines whether the signal circuit is shorted to any one of the 5-volt reference circuits. If a short exists, the corresponding sensor voltage will be pulled low.
4. 20 The previous step found the signal circuit and a 5-volt reference circuit shorted together. This test isolates whether the short is in the harness or within the TAC module.
5. 26 When the TAC module detects a condition within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting components during testing may set additional DTCs. Remember this if you review the stored information in Capture Info.

Scheme 624

Scheme 625

Scheme 626

The Throttle Position (TP) sensors 1 and 2 are potentiometer type sensors each with 3 circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A signal circuit.

The TP sensor are used to determine the throttle plate angle for various engine management systems. The control module provides each TP sensor a 5-volt reference circuit and a low reference circuit. The TP sensors then provide the control module with signal voltage proportional to throttle plate movement. Both TP sensor signal voltages are low at closed throttle and increase as the throttle opens. When the control module detects that TP sensor 1 signal and TP sensor 2 signals disagree or signal voltages are outside the predetermined range, this DTC set.

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

1. 21 When the TAC module detects a condition within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting components during testing may set additional DTCs. Remember this if you review the stored information in Capture Info.

Scheme 627

Scheme 628

See also:
• SENSOR OPERATING RANGE CHARTS - TRUCKS