Engine Control System - Self-Diagnostics - 4.2L: Overview Chevrolet TrailBlazer I

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 procedure reduces diagnostic time, and prevents the replacement of good parts.

Test Description

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

1. 2 - Lack of communication may be caused by a partial or a total malfunction of the Class 2 serial data circuit. The specified procedure determines the particular condition.
2. 5 - This step stores the Powertrain Control Module (PCM) Diagnostic Trouble Code (DTC) information into 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 procedure 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 «REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT»(ref-159085) article.
3. 6 - The presence of DTCs which begin with "U", indicate that some other module is not communicating. Following the specified procedure will gather all the available information before you perform the tests.
4. 8 - If there are other modules with DTCs set, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-155898-S19906497452003062800000) . 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 test directs you otherwise. System level DTCs, for example, misfire DTCs, fuel trim DTCs, and catalyst DTCs.
5. 10 - 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.

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 scan tool. Using 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 refers to the step numbers in the diagnostic procedures.

1. 1 - Any DTCs set, even those that are not listed in the «INSPECTION/MAINTENANCE SYSTEM DTCS»(ref-155898-S08605071532003062800000) 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 refers to the step numbers in the diagnostic procedures.

1. 1 - Make sure that you perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2 - This step runs the HO2S Heater Tests and initiates the EVAP System Test. Preprogramming 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 I/M 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 refers to the step numbers in the diagnostic procedures.

1. 1 - Make sure that you perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2 - Perform the Catalyst Test Runs 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-155898-S39274004852003062800000) .
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 the service information under 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 Evaporative (EVAP) emission system. The test may be used to set the I/M System Status indicators to YES. Service Bay Tests are included on scan tool for some systems depending upon vehicle make and model. The test is designed to allow the EVAP Diagnostic Tests to run in service bay conditions. Ensure that the vehicle meets the requirements listed in Conditions For Running before performing either EVAP System Test. Failure to meet the necessary requirements may produce inaccurate test results.

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

1. 1 - Make sure that you perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 3 - This step determines whether or not the EVAP System Test has passed. If the system is operating correctly, scan tool indicates that the system has passed and the I/M System Status updates to YES. If the EVAP Service Bay Test aborts because of lost enable conditions, the test can be repeated once the enable criteria is met.
3. 4 - A failed DTC during the EVAP Service Bay Test may not appear in the DTC Information display on some vehicles. The Service Bay Test displays an indication of which test failed as a directive to the appropriate service information. Some vehicles will display the test as aborted and the first failure of type "B" DTC appears in the DTC Information.
4. 5 - The EVAP System Test usually begins around an engine coolant temperature of 176°F (80°C). The vehicle should be operated moderately until this temperature is reached. The engine coolant temperature can be monitored using scan tool.
5. 6 - 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-155898-S19736575522003062800000) .
6. 7 - 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»(ref-155898-S11604503962003062800000) .
7. 8 - 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 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 refers to the step numbers in the procedures.

1. 1 - Make sure that you perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2 - 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-155898-S21852857482003062800000) .
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 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 refers to the step numbers in the procedures.

1. 1 - Make sure that you perform the I/M System Check before performing this test. Failure to do so may result in difficulty updating the status to YES.
2. 2 - Preprogramming 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-155898-S18072936342003062800000) .
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 the service information under 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.

Battery positive voltage is supplied directly to the Malfunction Indicator Light (MIL). The Powertrain Control Module (PCM) turns the MIL ON by grounding the MIL control circuit. There should be a steady Malfunction Indicator Light (MIL) with ignition on, with engine off.

MIL Operation

Malfunction Indicator Light (MIL) is located on the instrument panel.

MIL Function

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

MIL Illumination

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

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

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

Battery positive voltage is supplied directly to the Malfunction Indicator Light (MIL). The Powertrain Control Module (PCM) turns the MIL ON by grounding the MIL control circuit.

The Malfunction Indicator Light (MIL) is located on the instrument panel.

MIL Function

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

MIL Illumination

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

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

1. 2 - This step determines if the condition is with the MIL control circuit or the PCM.

The Camshaft Position (CMP) actuator is controlled by the PCM through a high control circuit and a low reference circuit. The high control circuit carries a 12-volt Pulse-Width Modulated (PWM) signal from the PCM to the CMP actuator solenoid in order to control the amount of engine oil flow to the cam phaser. The low reference circuit is used as a return circuit. The PCM has the ability to monitor the functionality of the high control and the low reference circuit. If the PCM detects an open, short to ground, or a short to voltage, DTC P0013 sets.

The cam phasing system is a hydraulically actuated phase shifting mechanism. The Powertrain Control Module (PCM) supplies the ignition positive driver and ground circuits. A Pulse-Width Modulated (PWM) driver controls the amount that the camshaft actuator solenoid assembly advances or retards the exhaust camshaft. The exhaust camshaft is commanded to a maximum retard position of 25 degrees. When the exhaust camshaft is retarded at the maximum rate, the duty cycle of the signal is at 100 percent. The maximum advance rate has a zero percent duty cycle. Other than when the camshaft is at full advance, a 50 percent duty cycle is used to maintain a steady retard angle. This DTC sets when the Desired and Actual Cam Phase angle error exceeds its tolerance value for a time period.

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 a 5-volt reference circuit, a low reference circuit, and a 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 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 on, with engine off, or at a Wide-Open Throttle (WOT). Certain vehicle models will also use the MAP sensor 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. DTC P0105 will set if the MAP sensor signal is not within the predicted range.

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

1. 4 - This step tests the ability of the MAP sensor to correctly indicate BARO.
2. 6 - This step tests the MAP sensor's ability to respond to an increase in engine vacuum.
3. 8 - This step tests for a proper MAP sensor pressure with an applied vacuum.

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. If the PCM detects a MAP sensor signal voltage that is excessively low, DTC P0107 will set.

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

1. 4 - If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records can help to locate an intermittent condition.

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 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 procedures.

1. 3 - If you cannot duplicate the DTC, use the information included in the Freeze Frame/Failure Records data in order to locate an intermittent condition.

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 sensor 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 sensor signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the IAT sensor signal circuit. If the PCM detects an excessively low IAT sensor 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 sensor 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 sensor circuit. With lower sensor resistance, the PCM detects a lower voltage on the IAT sensor circuit. If the PCM detects an excessively high IAT sensor voltage, indicating a low temperature, DTC P0113 sets.

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

1. 6 - This step tests for the proper operation of the circuit in the low voltage range.

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 sensor 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 sensor signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT sensor signal circuit. If the PCM detects an excessively low ECT sensor signal voltage, which is a high temperature indication, this 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 sensor 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 sensor signal circuit. With lower sensor resistance, the PCM detects a lower voltage on the ECT sensor signal circuit. If the PCM detects an excessively high ECT sensor signal voltage, which is a low temperature indication, DTC P0118 sets.

The Throttle Position (TP) sensors 1 and 2 are located within the throttle body assembly. Each sensor has its own 5-volt reference, low reference, and signal circuit. This provides the Powertrain Control Module (PCM) with a signal voltage proportional to throttle plate movement. TP sensor 1 signal voltage at closed throttle is about the 5-volt reference and decreases as the throttle plate is opened. TP sensor 2 signal voltage at closed throttle is about the low reference and increases as the throttle plate is opened. When the PCM detects a fault with both TP 1 and TP 2 the DTC sets.

The Throttle Position (TP) sensors 1 and 2 are located within the throttle body assembly. Each sensor has its own 5-volt reference, low reference, and signal circuit. This provides the Powertrain Control Module (PCM) with a signal voltage proportional to throttle plate movement. TP sensor 1 signal voltage at closed throttle is about the 5-volt reference and decreases as the throttle plate is opened. TP sensor 2 signal voltage at closed throttle is about the low reference and increases as the throttle plate is opened. When the PCM detects a fault with both TP 1 and 2, the DTC sets.

An Engine Coolant Temperature (ECT) sensor monitors the coolant temperature. The Powertrain Control Module (PCM) uses this input for engine control, and for an enabling criteria for some diagnostics. The air flow coming into the engine is accumulated. The air flow is used in order to determine if the engine has been driven within conditions that would allow the engine coolant to heat normally to the thermostat-regulating temperature. If the coolant temperature does not increase normally, or if the coolant temperature does not reach regulating temperature of the thermostat, 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. This DTC will set when there has been excessive time to reach Closed Loop fuel control.

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 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 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 engine is first started the PCM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates at greater than and less than bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream. If PCM detects the loop status is open too long, DTC P0130 will set.

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

1. 2 - An HO2S heater fault may set this DTC.
2. 3 - If the voltage is varying greater than and less than the specified value, the condition is not present.

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 engine is first started, the PCM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates greater than and less than bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream. If PCM detects an HO2S voltage that stays less than a specified value, DTC P0131 will set.

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

1. 2 - When system is operating correctly, the HO2S 1 voltage should toggle greater than and less than the bias voltage. You may need to operate the vehicle within the Freeze Frame conditions and Conditions for Setting the DTC in order to duplicate the malfunction that was detected by the PCM.
2. 4 - The specified value is what is measured on a correctly operating system.

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 engine is first started, the PCM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates greater than and less than bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream. If PCM detects an HO2S voltage that stays greater than the specified value, DTC P0132 will set.

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

1. 2 - When system is operating correctly, the HO2S 1 voltage should toggle greater than and less than the bias voltage. You may need to operate the vehicle within the Freeze Frame conditions and Conditions for Setting the DTC in order to duplicate the malfunction that was detected by the PCM.
2. 4 - The specified value is what is measured on a correctly operating system.

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 engine is first started, the PCM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates greater than and less than 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 greater than 600 mV to less than 300 mV or from less than 300 mV to more than 600 mV. If PCM detects that the transition time is too long, DTC P0133 will set.

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

1. 2 - When the system is operating correctly, the HO2S 1 voltage should toggle greater than and less than the specified values. You may need to operate the vehicle within the Freeze Frame conditions and Conditions for Setting the DTC in order to duplicate the malfunction that was detected by the PCM.
2. 4 - The specified value is what is measured on a correctly operating system.
3. 5 - The specified value is what is measured on a correctly operating system.

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 engine is first started, the PCM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates greater than and less than bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream.

If PCM detects that the HO2S voltage remains within the bias voltage range, DTC P0134 will set.

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

1. 2 - An HO2S heater fault may set this DTC.
2. 3 - If voltage is varying greater than and less than the specified value, the condition is not present.

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. 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, though a low side driver within the Powertrain Control Module (PCM). The PCM monitors the current flow through the heater for diagnosis.

If PCM detects that the HO2S heater current is greater than or less than a specified range, DTC P0135 or P0141 sets.

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 engine is first started, the PCM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1,000 mV that fluctuates greater than and less than bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream.

If PCM detects an HO2S voltage that stays less than a specified value, DTC P0137 will set.

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

1. 2 - When the system is operating correctly, the HO2S 2 voltage should toggle greater than and less than the bias voltage.
2. 3 - If voltage is varying greater than and less than the specified value, the condition is not present.

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 engine is first started, PCM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates greater than and less than bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream.

If PCM detects an HO2S voltage that stays greater than a specified value, DTC P0138 will set.

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

1. 2 - When the system is operating correctly, the HO2S 2 voltage should toggle greater than and less than the bias voltage.
2. 3 - This step tests the HO2S 2 high signal circuit for a short to voltage.

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 engine is first started, PCM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates greater than and less than bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream.

If PCM detects that the HO2S voltage remains within the bias voltage range, DTC P0140 will set.

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

1. 2 - An HO2S heater fault may set this DTC.
2. 3 - If voltage is varying greater than and less than the specified value, the condition is not present.

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 Loop and Closed Loop. During Open Loop, the PCM determines fuel delivery based on sensor signals, without oxygen sensor input. During Closed Loop, the PCM adds oxygen sensor inputs to calculate short and long term fuel trim (fuel delivery adjustments). Short Term fuel trim values change rapidly in response to the HO2S voltage signals. Long Term fuel trim makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. Fuel Trim Index is the average of Short and Long Term Fuel Trim and Purge Learn Memory based on engine speed and load. If the PCM detects an excessively lean condition, this DTC will set.

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

1. 7 - If conditions were not corrected, a worn cam, worn intake or exhaust valves, or other engine mechanical failures may be at fault.

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 during Open Loop 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). 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 Air/Fuel Ratio of 14.7:1. The Fuel Trim Index is the average of Short and Long Term Fuel Trim and Purge Learn Memory based on engine speed and load. 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 PCM detects an excessively rich condition, this DTC will set. If PCM detects excessive vapor then a pass is logged.

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

1. 6 - An EVAP canister that is saturated will cause a rich condition. Fuel in the vacuum line to the fuel pressure regulator indicates a bad regulator. If conditions were not corrected, a worn cam, worn intake or exhaust valves, or other engine mechanical failure may be at fault.

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 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 Light (MIL) will flash ON and OFF when the conditions for catalytic converter damage are present.

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

1. 2 - If actual CKP sensor variation values are not within the learned values, the misfire counters may increment.

The Powertrain Control Module (PCM) uses information from the Crankshaft Position (CKP) sensor and 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 the Three-Way Catalytic Converter (TWC) to overheat under certain driving conditions. The Malfunction Indicator Light (MIL) will flash ON and OFF when the conditions for TWC overheating are present. If PCM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC will set.

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

1. 2 - If the actual CKP sensor variation values are not within the learned values, the misfire counters may increment.

The Knock Sensor (KS) system enables the Powertrain Control Module (PCM) to control the ignition timing for the best possible performance while protecting the engine from potentially damaging levels of detonation. The PCM monitors 2 KS. Each KS produces an AC voltage signal that varies at all engine speeds and loads. The PCM adjusts the spark timing based on the amplitude and the frequency of the KS signal. The PCM receives the KS signal through a signal circuit. The KS ground is supplied by the PCM through a low reference circuit. The PCM uses the KS signal to calculate the average voltage and then assigns a voltage range value. The PCM should monitor a normal KS signal within the assigned voltage range. If the PCM malfunctions in a manner that will not allow proper diagnosis of the KS system, this DTC will set.

The Knock Sensor (KS) system enables the Powertrain Control Module (PCM) to control the ignition timing for the best possible performance while protecting the engine from potentially damaging levels of detonation. The PCM monitors 2 KS. Both sensors are located on the intake side of the engine block. KS 1 is located at the front of the engine. KS 2 is located at the rear of the engine. Each KS produces an AC voltage signal that varies at all engine speeds and loads. The PCM adjusts the spark timing based on the amplitude and the frequency of the KS signal. The PCM receives the KS signal through a signal circuit. The KS ground is supplied by the PCM through a low reference circuit. The PCM uses the KS signal to calculate the average voltage and then assigns a voltage range value. The PCM should monitor a normal KS signal within the assigned voltage range. If the PCM detects a KS signal outside of the assigned voltage range, or the KS signal is not present, this DTC will set. DTC P0327 refers to KS 1. DTC P0332 refers to KS 2.

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

1. 2 - This step ensures that the malfunction is present.
2. 3 - This step tests for a KS that is shorted to ground.
3. 4 - This step tests the KS for proper operation.
4. 5 - This step tests for a short to voltage on the KS signal circuit and the KS low reference circuit.

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

1. CKP sensor 1 signal circuit.
2. The low reference circuit.

If PCM detects no signal from the CKP sensor, DTC P0335 sets.

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

1. The CKP sensor 1 signal circuit.
2. The low reference circuit.

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

1. 4 - When a Medium Resolution Resync occurs, an engine stumble should also occur. If the electrical connection of a component or an electrical wire is malfunctioning, an engine stumble or a medium resolution resync may be induced by wiggling the circuit or electrical connector.
2. 5 - Operating malfunctioning, non-engine related electronic components may emit Electromagnetic Interference (EMI), which may cause a resync. This step determines if the medium resolution resyncs are being caused by an outside source.
3. 6 - Thoroughly check any suspected circuitry. See «DIAGNOSTIC AIDS»(ref-155898-S28405989682003062800000) .
4. 8 - An intermittent problem may be caused by a number of conditions. See «DIAGNOSTIC AIDS»(ref-155898-S28405989682003062800000) .
5. 11 - Program the replacement PCM and perform the Crankshaft Position System Variation Learn Procedure. See «POWERTRAIN CONTROL MODULE»(ref-155898-S06054808942003062800000) and «CRANKSHAFT POSITION SENSOR»(ref-155898-S34895643712003062800000) under PROGRAMMING.

The Camshaft Position (CMP) sensor produces a 6X plus a sync signal for each revolution of the camshaft. These signals are for control of sequential fuel injection and for exhaust camshaft phaser control. The CMP sensor is connected directly to the Powertrain Control Module (PCM) and consists of the following circuits

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

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

1. 6 - This step tests the output of the CMP sensor. If the duty cycle is not within the specified range, the sensor is bad.

The Camshaft Position (CMP) sensor produces a 6X plus a sync signal for each revolution of the camshaft. These signals are for control of sequential fuel injection and for exhaust camshaft phaser control. The CMP is connected directly to the Powertrain Control Module (PCM) and consists of the following circuits

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

If PCM receives a minimum number of CMP resyncs within a calculated amount of time, DTC P0341 will set.

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

1. 4 - The counter should stop incrementing with the sensor electrical connector disconnected and set a DTC P0341. If the counter stills increments, this indicates that the PCM is malfunctioning.

This diagnostic test is designed in order to measure the efficiency of the Three-Way Catalytic Converter (TWC) system. Catalytic converter efficiency is a measure of its ability to store oxygen after converting the levels of Hydrocarbon (HC), Carbon Monoxide (CO), and Oxides Of Nitrogen (NOx) to less harmful gases. The control module is able to evaluate the catalyst efficiency once the vehicle has met the enable criteria and the vehicle is at idle instead of the steady cruise speeds used in the past. Once the conditions for running this Diagnostic Trouble Code (DTC) are met, the control module commands either a lean or rich air/fuel ratio depending on the current state of the exhaust oxygen level. The control module issues a rich command if the exhaust is currently lean, or a lean command if the exhaust is currently rich. After completion of the first command, a second and opposite command is issued. For example, if the control module were to command a rich mixture, the upstream Heated Oxygen Sensor (HO2S) voltage would increase immediately. The rich mixture is delayed in reaching the downstream HO2S due to the conversion process occurring within the converter. The higher the efficiency, the more the delay before the rich or lean mixture is detected by the downstream Oxygen Sensor (O2S). As a result of the lower conversion efficiency within a damaged or poisoned catalyst, the delay in the rich or lean mixture reaching the downstream O2S is significantly shorter. This DTC monitors the amount of time required for both the upstream and downstream HO2S voltages to cross a calibrated voltage threshold in response to the rich or lean command.

The Evaporative (EVAP) emission large leak test applies vacuum to the EVAP system and monitors vacuum decay. The Powertrain Control Module (PCM) monitors the Fuel Tank Pressure (FTP) sensor signal to determine the vacuum decay rate. At an appropriate time, the PCM turns the EVAP canister purge valve ON (open) and the EVAP vent valve ON (closed). This allows the engine to draw a vacuum on the EVAP system. At a calibrated time, or vacuum level, the PCM turns the purge valve OFF (closed), sealing the system, and monitors the FTP sensor input in order to determine EVAP system vacuum. If the system is unable to achieve the calibrated vacuum level, or the vacuum level decreases too rapidly, DTC P0440 will set.

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

1. 3 - This test verifies that the EVAP purge solenoid is electrically functional.
2. 4 - This test verifies that the EVAP vent solenoid is electrically functional.
3. 9 - 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.
4. 11 - This test verifies that the Fuel Tank Pressure (FTP) sensor is accurate. An FTP sensor that does not correctly respond to vacuum, or pressure may cause this DTC to set.

The Evaporative (EVAP) emission small leak test applies vacuum to the EVAP system and monitors vacuum decay. The Powertrain Control Module (PCM) monitors the Fuel Tank Pressure (FTP) sensor signal to determine the vacuum decay rate. At an appropriate time, the PCM turns the EVAP canister purge valve ON (open) and the EVAP vent valve ON (closed). This allows the engine to draw a vacuum on the EVAP system. At a calibrated time, or vacuum level, the PCM turns the purge valve OFF (closed), sealing the system, and monitors the FTP sensor input in order to determine EVAP system vacuum decay. If the system detects a leak larger than a calibrated amount, DTC P0442 will set.

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

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.

A restricted or blocked Evaporative (EVAP) emission vent path is detected by the Powertrain Control Module (PCM) commanding the purge valve ON (open) and the vent valve ON (closed) allowing a vacuum to be applied to the EVAP system. Once a calibrated vacuum level has been reached, the PCM commands the purge valve OFF (closed) and the vent valve OFF (open) while monitoring the Fuel Tank Pressure (FTP) sensor for a decrease in vacuum. If the vacuum does not decrease to about zero in. H2O in a calibrated time, DTC P0446 will set.

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

1. 5 - This step inspects the EVAP vent solenoid electrical operation.
2. 6 - This step inspects for a restricted EVAP vent solenoid.
3. 7 - This step tests if the restriction is in the EVAP canister or the vent hose.

The Powertrain Control Module (PCM) monitors the Fuel Tank Pressure (FTP) sensor signal in order to detect vacuum decay and excess vacuum during the enhanced Evaporative (EVAP) emission diagnostic. The PCM supplies a 5-volt reference and ground to the sensor. The FTP sensor signal voltage increases as the fuel tank pressure decreases (negative pressure or vacuum, high voltage). The FTP sensor signal voltage decreases as the fuel tank pressure increases (positive pressure, low voltage). When the FTP sensor signal goes below a predetermined value, DTC P0452 will set.

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

1. 2 - This step verifies that the condition is present.
2. 4 - This step tests the 5-volt reference of the FTP sensor.
3. 5 - This step tests if another component is causing the 5-volt reference circuit condition.
4. 6 - If scan tool displays 5 volts, the FTP sensor signal circuit, FTP sensor 5-volt reference circuit, and control module are okay.

The Powertrain Control Module (PCM) monitors the Fuel Tank Pressure (FTP) sensor signal in order to detect vacuum decay and excess vacuum during the enhanced Evaporative (EVAP) emission diagnostic. The PCM supplies a 5-volt reference and ground to the sensor. The FTP sensor signal voltage increases as the fuel tank pressure decreases (negative pressure or vacuum, high voltage). The FTP sensor signal voltage decreases as the fuel tank pressure increases (positive pressure, low voltage). When the FTP sensor signal voltage goes more than a predetermined value, DTC P0453 will set.

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

1. 2 - This step determines if the condition is present.
2. 4 - This step tests the signal circuit of the FTP sensor.
3. 5 - This step tests the ground circuit of the FTP sensor.
4. 6 - This step tests the 5-volt reference circuit of the FTP sensor.

The Vehicle Speed Sensor (VSS) assembly provides vehicle speed information to the Powertrain Control Module (PCM). The VSS assembly is a permanent magnet generator. The VSS produces an AC voltage as rotor teeth on the transmission output shaft pass through the sensor's magnetic field. The AC voltage level and the number of pulses increase as the speed of the vehicle increases. The PCM converts the pulsing voltage to vehicle speed. The PCM uses the vehicle speed signal to determine shift timing and Torque Converter Clutch (TCC) scheduling. When the PCM detects a low vehicle speed when there is a high engine speed in a drive gear range, then DTC P0502 sets.

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

1. 3 - This step tests the VSS assembly circuit.
2. 4 - This step tests the integrity of the VSS assembly.

The Vehicle Speed Sensor (VSS) assembly provides vehicle speed information to the Powertrain Control Module (PCM). The VSS assembly is a permanent magnet generator. The VSS produces an AC voltage as rotor teeth on the transmission output shaft pass through the sensor's magnetic field. The AC voltage level and the number of pulses increase as the speed of the vehicle increases. The PCM converts the pulsing voltage to vehicle speed. The PCM uses the vehicle speed signal to determine shift timing and Torque Converter Clutch (TCC) scheduling. When the PCM detects an unrealistically large drop in vehicle speed, then DTC P0503 sets.

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

1. 3 - This step tests the VSS assembly circuit.
2. 4 - This step tests the integrity of the VSS assembly.

The Throttle Actuator Control (TAC) motor is controlled by the Powertrain Control Module (PCM). The DC motor located in the throttle body drives the throttle plate. In order to decrease idle speed, the PCM commands the throttle closed reducing air flow into the engine and the idle speed decreases. In order to increase idle speed, the PCM commands the throttle plate open allowing more air to pass the throttle plate. If the actual idle RPM does not match the desired idle RPM within a calibrated time, this DTC sets.

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

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

The Throttle Actuator Control (TAC) motor is controlled by the Powertrain Control Module (PCM). The DC motor located in the throttle body drives the throttle plate. In order to decrease idle speed, the PCM commands the throttle closed reducing air flow into the engine and the idle speed decreases. In order to increase idle speed, the PCM commands the throttle plate open allowing more air to pass the throttle plate. If the actual idle RPM does not match the desired idle RPM within a calibrated time, this DTC sets.

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

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

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 refers to the step numbers in the diagnostic procedures.

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

The Throttle Position (TP) sensors 1 and 2 are located within the throttle body assembly. Each sensor has the following components

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

This provides the Powertrain Control Module (PCM) with a signal voltage proportional to throttle plate movement. TP sensor 1 signal voltage at closed throttle is about 5-volt reference and decreases as the throttle plate is opened. TP sensor 2 signal voltage at closed throttle is about the low reference and increases as the throttle plate is opened. When TP sensor 1 signal voltage is not within the predicted range, this DTC sets.

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 engine is first started, PCM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates greater than and less than 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 of rich-to-lean and lean-to-rich transitions. A transition is defined as the HO2S voltage changes from greater than 600 mV to less than 300 mV or from less than 300 mV to greater than 600 mV. If the PCM detects that the number of transitions were less than a specified value, DTC P1133 will set.

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

1. 2 - When the system is operating correctly, the HO2S 1 voltage should toggle greater than and less than the specified values. You may need to operate the vehicle within the Freeze Frame conditions and Conditions for Setting the DTC in order to duplicate the malfunction that was detected by the PCM.
2. 4 - The specified value is what is measured on a correctly operating system.
3. 5 - The specified value is what is measured on a correctly operating system.

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 engine is first started, PCM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates greater than and less than 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 transitions. A transition is defined as the HO2S voltage changes from greater than 600 mV to less than 300 mV or from less than 300 mV to greater than 600 mV. If PCM detects that the transition time ratio is not within a specified range, DTC P1134 will set.

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

1. 2 - When the system is operating correctly, the HO2S 1 voltage should toggle greater than and less than the specified values. You may need to operate the vehicle within the Freeze Frame conditions and Conditions for Setting the DTC in order to duplicate the malfunction that was detected by the PCM.
2. 4 - The specified value is what is measured on a correctly operating system.
3. 5 - The specified value is what is measured on a correctly operating system.

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 temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1,000 mV that fluctuates greater than and less than bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream.

If PCM detects an HO2S voltage that stays less than a specified value, DTC P1137 will set.

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

1. 2 - When the system is operating correctly, the HO2S 2 voltage should toggle greater than and less than the bias voltage.

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 engine is first started, PCM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates greater than and less than bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream.

If PCM detects an HO2S voltage that stays greater than a specified value, DTC P1138 will set.

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

1. 2 - When the system is operating correctly, the HO2S 2 voltage should toggle greater than and less than the specified values. You may need to operate the vehicle within the Freeze Frame conditions and Conditions for Setting the DTC in order to duplicate the malfunction that was detected by the PCM.
2. 6 - Disconnecting the HO2S 2 and connecting a jumper wire between the HO2S 2 high signal circuit and the HO2S 2 low signal circuit to ground, should cause the scan tool to display HO2S 2 voltage less than 100 mV. If the signal voltage is still high, this indicates that the PCM is malfunctioning.

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 engine is first started, PCM operates in Open Loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperatures and Closed Loop is achieved, the HO2S generates a voltage within a range of 0-1000 mV that fluctuates greater than and less than bias voltage. High HO2S voltage indicates a rich exhaust stream. Low HO2S voltage indicates a lean exhaust stream.

If PCM detects an HO2S voltage that stays less than a specified value, DTC P1171 will set.

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

1. 2 - When the system is operating correctly, the HO2S 1 voltage should toggle greater than and less than the bias voltage. You may need to operate the vehicle within the Freeze Frame conditions and Conditions for Setting the DTC in order to duplicate the malfunction that was detected by the PCM.
2. 5 - The specified value is what is measured on a correctly operating system.

The Throttle Position (TP) sensors 1 and 2 are located within the throttle body assembly. Each sensor has the following components

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

This provides the Powertrain Control Module (PCM) with a signal voltage proportional to throttle plate movement. TP sensor 1 signal voltage at closed throttle is about the 5-volt reference and decreases as the throttle plate is opened. TP sensor 2 signal voltage at closed throttle is about the low reference and increases as the throttle plate is opened. When TP sensor 2 signal voltage is not within the predicted range, this DTC sets.

The throttle actuator control assembly has 2 Throttle Position (TP) sensors mounted within the assembly. The Powertrain Control Module (PCM) provides individual signal, ground, and 5-volt reference circuits to each sensor. Both sensors operate within a voltage range between 0.35-4.65 volts. When the throttle is opened from zero to 100 percent, one sensor signal voltage increases while the other decreases. The signal circuit for TP sensor 1 is referenced to ground, and the signal circuit for TP sensor 2 is pulled up to 5 volts within the PCM.

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

1. 6 - This step checks the integrity of the 5-volt reference and ground circuits of the TP sensors.
2. 7 - This step determines if the 5-volt reference circuit or the sensor ground circuit is the cause of the DTC.
3. 8 - If scan tool displays 100 percent for the TP sensor 1 and the TP sensor 2 angle, this indicates that the TP sensor signal circuits are not the cause of the DTC.
4. 9 - This step checks for excessive resistance in the TP sensor 5-volt reference circuit between the TP sensor harness connector and the PCM harness connector.
5. 10 - This step checks for excessive resistance in the TP sensor ground circuit between the TP sensor harness connector and the PCM harness connector.
6. 11 - This step checks for the TP sensor signal circuits for being shorted to another circuit in the PCM wiring harness between the PCM and the TP sensor wiring harness.
7. 16 - When the PCM detects a problem within the throttle control system, more than one related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing one individual problem may correct more than one DTC. Keep this in mind when reviewing captured DTC info.

The Accelerator Pedal Position (APP) sensors 1 and 2 are located within the accelerator pedal assembly. Each sensor has the following circuits

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

This provides the Powertrain Control Module (PCM) with a signal voltage proportional to accelerator pedal movement. The APP sensor 1 signal voltage at rest position is about the low reference and increases as the pedal is actuated. The APP sensor 2 signal voltage at rest position is about the 5-volt reference and decreases as the pedal is actuated.

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

1. 2 - Any circuit faults on either APP sensor 1 or 2 will set one of the DTCs listed. Refer to the appropriate test for diagnosis.

The Accelerator Pedal Position (APP) sensors 1 and 2 are located within the accelerator pedal assembly. Each sensor has the following circuits

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

This provides the Powertrain Control Module (PCM) with a signal voltage proportional to accelerator pedal movement. The APP sensor 1 signal voltage at rest position is about the low reference and increases as the pedal is actuated. The APP sensor 2 signal voltage at rest position is about the 5-volt reference and decreases as the pedal is actuated. When APP sensor 1 signal voltage is not within the predicted range, this code sets.

The Accelerator Pedal Position (APP) sensors 1 and 2 are located within the accelerator pedal assembly. Each sensor has the following circuits

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

This provides the Powertrain Control Module (PCM) with a signal voltage proportional to accelerator pedal movement. The APP sensor 1 signal voltage at rest position is about the low reference and increases as the pedal is actuated. The APP sensor 2 signal voltage at rest position is about the 5-volt reference and decreases as the pedal is actuated. When APP sensor 2 signal voltage is not within the predicted range, this DTC sets.

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

The Powertrain Control Module (PCM) uses the crankshaft sensor and the camshaft sensor information to monitor the correlation between the crankshaft and camshaft positions. This DTC will set if the deviation between the crankshaft and camshaft exceeds a calibrated amount.

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

1. 2 - If this sets, there is a problem with the camshaft position actuator solenoid high control circuit shorted to voltage or the solenoid stuck open.

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 vehicle is operating on a rough road. If ABS is detecting a rough road condition severe enough to effect misfire detection, a rough road signal is sent to 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 rotation 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 P1381 will set.

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

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

This DTC tests for undesired intake manifold vacuum flow to the Evaporative (EVAP) emission system. The Powertrain Control Module (PCM) seals the EVAP system by commanding the EVAP purge valve OFF (closed) and the EVAP vent valve ON (closed). The PCM monitors the Fuel Tank Pressure (FTP) sensor to determine if a vacuum is being drawn on the EVAP system. If the vacuum in the EVAP system is more than a calibrated value within a calibrated time, DTC P1441 will set.

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

1. 2 - This step inspects for a leaking EVAP purge solenoid.
2. 4 - Removing the fuel fill cap will equalize the pressure inside the tank with atmospheric pressure. At zero in. H2O, the FTP sensor should be about 1.5 volts. If sensor is not, there is a concern with the sensor or related wiring.

The commanded throttle position is compared to the actual throttle position based on accelerator pedal position and possibly other limiting factors. Both values should be within a calibrated range of each other. The Powertrain Control Module (PCM) continuously monitors the commanded and actual throttle positions. This DTC sets if the values are greater than the calibrated range.

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

1. 8 - The throttle valve is spring loaded in a slightly open position and should move in either direction without binding. The throttle valve should always be under spring pressure.
2. 11 - When ignition is turned on, PCM operates the throttle control motor to verify the integrity of the system prior to start-up. This can be seen by the momentary flash of the test light as the ignition is turned ON.

The Powertrain Control Module (PCM) uses the following information in order to calculate an expected airflow rate

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

If PCM detects the airflow rate is more than expected, DTC P1514 sets.

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

1. 5 - This step will determine if the Manifold Absolute Pressure (MAP) sensor voltage is within the proper range at idle.
2. 6 - This step will determine if the MAP sensor responds properly to the change in manifold pressure.
3. 7 - A throttle blade that sticks or binds may set this code. Opening the throttle through the entire range will indicate problems such as these.
4. 9 - When the PCM detects a condition within the ETC system, other DTCs may set due to the many redundant tests run continuously on this system. Locating and repairing one individual condition may correct more than one DTC. Keep this in mind when reviewing captured DTC info.

The commanded throttle position is compared to the actual throttle position based on accelerator pedal position and possibly other limiting factors. Both values should be within a calibrated range of each other. The Powertrain Control Module (PCM) continuously monitors the commanded and actual throttle positions. This DTC sets if the values are greater than the calibrated range.

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

1. 8 - The throttle valve is spring loaded in a slightly open position and should move in either direction without binding. The throttle valve should always be under spring pressure.
2. 11 - When ignition is turned on, PCM operates the throttle control motor to verify the integrity of the system prior to start-up. This can be seen by the momentary flash of the test light as the ignition is turned ON.

The commanded throttle position is compared to the actual throttle position based on Accelerator Pedal Position (APP) and possibly other limiting factors. Both values should be within a calibrated range of each other. The Powertrain Control Module (PCM) continuously monitors the commanded and actual throttle positions. This DTC sets if the values are greater than the calibrated range.

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

1. 8 - The throttle valve is spring loaded in a slightly open position and should move in either direction without binding. The throttle valve should always be under spring pressure.
2. 11 - When ignition is turned on, the PCM operates the throttle control motor to verify the integrity of the system prior to start-up. This can be seen by the momentary flash of the test light as the ignition is turned on.

During Battery Saver Mode, the Powertrain Control Module (PCM) determines if the throttle plate is returning to the correct de-energized position. If the PCM determines the throttle plate is not at the correct position during battery saver mode, this DTC is set.

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

1. 8 - More than one ETC system related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing one individual condition may correct more than one DTC. Keep this in mind when reviewing captured DTC info.

The Powertrain Control Module (PCM) receives the following ignition inputs from the ignition switch

1. Ignition 0 signal.
2. Ignition 1 signal.
3. Crank signal

The PCM uses a Class II Ignition mode message and the voltage input from 2 separate systems to test the ignition 0 circuit. If PCM detects an improper ignition 0 signal, DTC P1633 will set.

The Powertrain Control Module (PCM) provides a 5-volt reference to the following sensors

1. Throttle Position (TP) sensor 1.
2. Accelerator Pedal Position (APP) sensor 2.
3. A/C pressure sensor.
4. Fuel Tank Pressure (FTP) sensor.
5. Oil Pressure Sensor (OPS).

The PCM monitors voltage on the 5-volt reference circuit. If the voltage is higher or lower than required, DTC P1635 will set.

The Powertrain Control Module (PCM) provides a 5-volt reference to the following sensors

1. Throttle Position (TP) sensor 2.
2. Accelerator Pedal Position (APP) sensor 1.
3. Manifold Absolute Pressure (MAP) sensor.

The PCM monitors voltage on the 5-volt reference circuit. If the voltage is higher or lower than required, DTC P1639 will set.

The Throttle Actuator Control (TAC) system uses an ignition voltage supply separate from the PCM supply. If PCM detects a voltage difference between the 2 circuits, this DTC will set.

See also:
• SENSOR OPERATING RANGE CHARTS - TRUCKS