Engine Control System - Self-Diagnostics - 4.2L: Overview Oldsmobile Bravada III

MODEL IDENTIFICATION

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

MODEL IDENTIFICATION

Description

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

Test Description

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

1. 2 Lack of communication may be caused by a partial or a total malfunction of the Class 2 serial data circuit. The specified procedure determines the particular condition.
2. 5 This step stores the 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 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 appropriate REMOVAL, OVERHAUL & INSTALLATION article.
3. 6 The presence of DTCs which begin with "U", indicate that some other module is not communicating. Following the specified procedure will gather all the available information before you perform the tests.
4. 8 If there are other modules with DTCs set, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-132531-S07878208602002012100000) . 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. 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 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 on the diagnostic procedures.

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

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

The numbers below refer to the step numbers on 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 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 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 refer to the step numbers on 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 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-132531-S41003123072002012100000) .
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 the 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 refer to the step numbers on 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, the 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 the 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-132531-S08701937372002012100000) .
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 DTC.
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 refer to the step numbers on 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-132531-S29193710982002012100000) .
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 refer to the step numbers on 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 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-132531-S35935659722002012100000) .
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 Lamp (MIL). The Powertrain Control Module (PCM) turns the MIL ON by grounding the MIL control circuit. There should be a steady Malfunction Indicator Lamp (MIL) with the ignition ON and the engine OFF.

MIL Operation

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

The numbers below refer to the step numbers on 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 Lamp (MIL). The Powertrain Control Module (PCM) turns the MIL ON by grounding the MIL control circuit.

The Malfunction Indicator Lamp (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. The MIL will illuminate with the ignition ON and the engine not running.
2. The MIL will turn OFF when the engine is started.
3. The MIL will remain ON if the self-diagnostic system has detected a malfunction.
4. The MIL may turn OFF if the malfunction is not present.
5. If the MIL is illuminated and then the engine stalls, the MIL will remain illuminated so long as the ignition switch is ON.
6. If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition switch is cycled OFF, 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 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 0 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. The driver has the ability to detect an electrical malfunction in the ignition positive or ground circuit. If an electrical malfunction occurs, the driver signals the PCM to set this Diagnostic Trouble Code (DTC).

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 0 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 Diagnostic Trouble Code (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 is ON, with the 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 refer to the step numbers on the diagnostic procedures.

1. 3 This step tests the MAP sensor's ability to correctly indicate barometric pressure. The value shown for the MAP sensor varies with altitude. 103 kPa is the approximate Barometric (BARO) pressure displayed at or near sea level.
2. 5 This step tests the MAP sensor's ability to respond to an increase in engine vacuum.
3. 6 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 numbers below refer to the step numbers on the diagnostic procedures.

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

1. 3 Operate the vehicle within the same conditions as when the DTC failed. If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records can aid in locating 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 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 operation of the circuit in the low voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to voltage.

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

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

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

The Engine Coolant Temperature (ECT) sensor is a variable resistor, sometimes called a thermistor, that measures the temperature of the engine coolant. The 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. 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 number below refers to the step number in the diagnostic procedures.

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

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 near the 5-volt reference and decreases as the throttle plate is opened. TP sensor 2 signal voltage at closed throttle is near 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 Diagnostic Trouble Code (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 near the 5-volt reference and decreases as the throttle plate is opened. TP sensor 2 signal voltage at closed throttle is near 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 Diagnostic Trouble Code (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 Diagnostic Trouble Code (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 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 on the diagnostic procedures.

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.

When the vehicle is first started, the engine operates in an Open Loop operation, ignoring the heated oxygen sensor signal and calculating the air/fuel ratio based on inputs from the Engine Coolant Temperature (ECT), the Throttle Position (TP), and the manifold absolute pressure (MAP) sensors only. The Powertrain Control Module (PCM) will begin by using the Heated Oxygen Sensor (HO2S) signal for controlling the fuel delivery (Closed Loop) when the following conditions are met

1. The engine has run a minimum amount of time based on ECT at engine start up.
2. The Heated Oxygen Sensor 1 (HO2S 1) has a varying voltage output showing that the sensor is hot enough to operate properly.
3. The ECT has increased a minimum amount based on the ECT at engine start up.

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

1. 2 When the system is operating correctly the HO2S voltage should toggle above and below the specified values.
2. 5 The specified value is what is measured on a correctly operating system.
3. 6 The specified value is what is measured on a correctly operating system.

The Powertrain Control Module (PCM) supplies a voltage of about 447 mV between the Heated Oxygen Sensor 1 (HO2S 1) high signal and the low signal circuit. The HO2S 1 varies the voltage within a range of about 1000 mV if the exhaust is rich, down through about 100 mV if the exhaust is lean. The sensor is like an open circuit and produces no voltage when below 600°F (315°C). Do not attempt to repair the HO2S. Replace the entire HO2S if the following conditions exist

1. Damaged wiring.
2. Damaged electrical connector.
3. Damaged terminals.

The Powertrain Control Module (PCM) supplies a voltage of about 447 mV between the Heated Oxygen Sensor 1 (HO2S 1) high signal and the low signal circuit. The HO2S 1 varies the voltage within a range of about 1000 mV if the exhaust is rich, down through about 100 mV if the exhaust is lean. The sensor is like an open circuit and produces no voltage when below 600°F (315°C). Do not attempt to repair the HO2S. Replace the entire HO2S if the following conditions exist

1. Damaged wiring.
2. Damaged electrical connector.
3. Damaged terminals.

The Powertrain Control Module (PCM) continuously monitors the Heated Oxygen Sensor 1 (HO2S 1) activity for 100 seconds. During the monitor period, the PCM counts the number of times that the HO2S 1 switches from rich to lean and from lean to rich and adds the amount of time that the HO2S 1 took in order to complete all of the switches. With this information, you can determine an average time for all of the switches. If the average time to switch is too slow, a DTC P0133 will set. Do not attempt to repair the HO2S. Replace the entire HO2S if the following conditions exist

1. Damaged wiring.
2. Damaged electrical connector.
3. Damaged terminals.

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

1. 2 When the system is operating correctly, the HO2S voltage should toggle above and below the specified values.
2. 5 The specified value is what is measured on a correctly operating system.
3. 6 The specified value is what is measured on a correctly operating system.

The Powertrain Control Module (PCM) supplies a voltage of about 447 mV between the Heated Oxygen Sensor 1 (HO2S 1) high signal and the low signal circuit. The HO2S 1 varies the voltage within a range of about 1000 mV if the exhaust is rich, down through about 100 mV if the exhaust is lean. The sensor is like an open circuit and produces no voltage when below 600°F (315°C). Do not attempt to repair the HO2S. Replace the entire HO2S 1 assembly if the following conditions exist

1. Damaged wiring.
2. Damaged electrical connector.
3. Damaged terminals.

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

1. 2 When the system is operating correctly, the HO2S voltage should toggle above and below the specified values.
2. 5 The specified value is what is measured on a correctly operating system.
3. 6 The specified value is what is measured on a correctly operating system.

Heated Oxygen Sensors (HO2S) are used to minimize the amount of time required to enter Closed Loop fuel control operation and to allow accurate catalyst monitoring. The HO2S heater is fed power directly from ignition 1. The HO2S heater control circuit or heater ground is connected to the Powertrain Control Module (PCM). The PCM controls HO2S heater operation by grounding the control circuit via an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. The driver for the HO2S heater control circuit has the ability to measure the amount of current drawn by the controlled device.

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

1. 2 Allow the engine to cool before performing this test. This allows the HO2S to cool which causes the HO2S signal voltage to return to near bias voltage, approximately 450 mV. This test determines if ground is constantly being applied to the HO2S heater.
2. 3 After the HO2S heater is commanded ON, the HO2S will heat up. This will cause the signal voltage to change either more than or less than bias voltage, verifying the HO2S heater is operating.
3. 4 This step tests for voltage at the HO2S heater. The O2 fuse supplies power to the HO2S heater.
4. 5 This step verifies that the PCM is providing ground to the HO2S heater.
5. 6 This step tests if ground is constantly being applied to the HO2S heater.
6. 11 If more than one HO2S DTC is set, this is a good indication that the O2 fuse is open. Test all related circuits going to all the heated oxygen sensors for a short to ground. If you cannot locate a shorted circuit, it may be necessary to disconnect each HO2S one at a time to locate a shorted sensor.

In order to control emissions, a catalytic converter converts any harmful exhaust emissions into harmless water vapor and carbon dioxide. The Powertrain Control Module (PCM) has the capability to monitor this process by using a rear Heated Oxygen Sensor 2 (HO2S 2). The HO2S 2, located in the exhaust stream past the catalytic converter, produces an output signal which indicates the storage capacity of the catalyst. This in turn indicates the catalysts ability to convert the exhaust emissions effectively. If the catalyst is functioning properly, the HO2S 2 signal will be far less active than the signal produced by the front oxygen sensor (HO2S 1). Do not attempt to repair the HO2S 2. Replace the entire HO2S 2 assembly if the following conditions exist

1. Damaged wiring.
2. Damaged electrical connector.
3. Damaged terminals.

Obstruction of the air reference and degraded HO2S 2 performance could result in any attempt to repair the above conditions. The HO2S 2 must have a clean air reference in order for the HO2S 2 to function properly. This clean air reference is obtained by way of the HO2S 2 wires.

In order to control emissions, a catalytic converter converts any harmful exhaust emissions into harmless water vapor and carbon dioxide. The Powertrain Control Module (PCM) has the capability to monitor this process by using a rear Heated Oxygen Sensor 2 (HO2S 2). The HO2S 2, located in the exhaust stream past the catalytic converter, produces an output signal which indicates the storage capacity of the catalyst. This in turn indicates the catalysts ability to convert the exhaust emissions effectively. If the catalyst is functioning properly, the HO2S 2 signal will be far less active than the signal produced by the front oxygen sensor (HO2S 1). Do not attempt to repair the HO2S 2. Replace the entire HO2S 2 assembly if the following conditions exist

1. Damaged wiring.
2. Damaged electrical connector.
3. Damaged terminals.

Obstruction of the air reference and degraded HO2S 2 performance could result in any attempt to repair the above conditions. The HO2S 2 must have a clean air reference in order for the HO2S 2 to function properly. This clean air reference is obtained by way of the HO2S 2 wires.

In order to control emissions, a catalytic converter converts any harmful exhaust emissions into harmless water vapor and carbon dioxide. The Powertrain Control Module (PCM) has the capability to monitor this process by using a rear Heated Oxygen Sensor 2 (HO2S 2). The HO2S 2, located in the exhaust stream past the catalytic converter, produces an output signal which indicates the storage capacity of the catalyst. This in turn indicates the catalysts ability to convert the exhaust emissions effectively. If the catalyst is functioning properly, the HO2S 2 signal will be far less active than the signal produced by the front oxygen sensor (HO2S 1). Do not attempt to repair the HO2S 2. Replace the entire HO2S 2 assembly if the following conditions exist

1. Damaged wiring.
2. Damaged electrical connector.
3. Damaged terminals.

Obstruction of the air reference and degraded HO2S 2 performance could result in any attempt to repair the above conditions. The HO2S 2 must have a clean air reference in order for the HO2S 2 to function properly. This clean air reference is obtained by way of the HO2S 2 wires.

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

1. 6 Disconnecting the HO2S 2 and connecting a jumper wire between the HO2S 2 high signal circuit and the HO2S 2 low signal circuit will determine if the PCM or wiring or HO2S 2 is malfunctioning.

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 Diagnostic Trouble Code (DTC) will set.

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

1. 5 If conditions were not corrected, see appropriate BASIC DIAGNOSTIC PROCEDURES 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.

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 the PCM detects an excessively rich condition, this Diagnostic Trouble Code (DTC) will set. If the PCM detects excessive vapor then a pass is logged.

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

1. 5 If conditions were not corrected, see appropriate BASIC DIAGNOSTIC PROCEDURES article.
2. 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 numbers below refer to the step numbers on the diagnostic procedures.

1. 2 The misfire current counters may not increment if certain DTCs are set. Use a scan tool to clear the DTCs. Monitoring the misfire current counters isolates which fuel injector is not operating. A cylinder that is misfiring can also cause the misfire current counters to increment for another cylinder. Diagnose the cylinder with the highest level of misfire first.
2. 4 This step isolates the condition. If the test lamp flashes, the PCM is providing ground to the fuel injector.
3. 5 This step tests if a ground is constantly being applied to the fuel injector.
4. 6 This step isolates the circuit between the multi-way connector and the PCM. An open or short to voltage on the fuel injector control circuit will not allow the test lamp to flash.
5. 8 This step inspects for fuel injector harness damage between the multi-way connector and the fuel injector. Careful inspection may isolate the condition before removal of the intake manifold.
6. 10 Perform the continuity test at the multi-way connector. If the Digital Multimeter (DMM) displays OL, test the circuits for an open or a poor connection.
7. 13 This step isolates the circuit between the multi-way connector and the fuel injector. A short to voltage on the fuel injector control circuit will set this DTC.

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.

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

1. 2 Engine misfire can change engine load characteristics which may affect the Throttle Position (TP) sensor performance diagnostic. Correct any misfire before diagnosing. A malfunctioning injector circuit, crankshaft position system variation not learned, an intermittent CKP sensor problem, incorrect rough road data from the Electronic Brake Control Module (EBCM), etc. may cause a misfire DTC to be set. If any other DTCs are set with DTC P0300, diagnose and repair the other DTC before using the DTC P0300 table.
2. 3 The Misfire Bar Graph (or Misfire Current Cyl #) display may normally display a small amount of activity (0-10 counts) but should not steadily increment during an entire 200 revolution test sample period.
3. 4 A misfiring cylinder can sometimes affect the misfire counters for other cylinders. When performing this table, concentrating on the cylinder with the highest level of misfire and correcting the problem, may also correct the other cylinders that indicate misfire. This step splits the table between conditions that would cause a specific cylinder to misfire and conditions that would affect all cylinders, causing a random multiple cylinder misfire.

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. DTCs P0301 through P0306 correspond to cylinders 1 through 6. If the PCM is able to determine that a specific cylinder is misfiring, the Diagnostic Trouble Code (DTC) for that cylinder will set. If the misfire is random and on multiple cylinders, DTC P0300 will set. 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.

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

1. 2 DTCs that may cause a misfire DTC to set may include those for injector control circuits, oxygen sensors, the Evaporative (EVAP) emission system, or fuel trim.
2. 7 This test is to determine if there is a problem in the Heated Oxygen Sensor (HO2S) or wiring that is causing the PCM to alter the fuel trim. When the sensors are disconnected, the fuel system should go into Open Loop. If the misfire counters stop incrementing, perform the HO2S diagnosis for sensor 1.

The knock sensor (KS) produces an AC voltage at all engine speeds and loads. The Powertrain Control Module (PCM) then adjusts the spark timing based on the amplitude and frequency of the KS signal. The PCM uses the KS signal to calculate the average voltage. Then the PCM assigns a voltage value. The PCM checks the knock sensor and related wiring by comparing the actual knock signal to the assigned voltage range. A normal KS signal should stay outside the assigned voltage range. This Diagnostic Trouble Code (DTC) will set if the PCM malfunctions in a manner that will not allow proper diagnosis of the KS system. The KS system uses 2 knock sensors. Both sensors are connected directly to the PCM using the following circuits

1. The KS 1 signal circuit.
2. The KS 1 low reference circuit.
3. The KS 2 signal circuit.
4. The KS 2 low reference circuit.

KS 1 is at the front of the engine, or nearest the accessory belt. KS 2 is at the rear of the engine, or nearest the driveplate. Both sensors are on the intake side of the block.

The knock sensor (KS) produces an AC voltage at all engine speeds and loads. The Powertrain Control Module (PCM) then adjusts the spark timing based on the amplitude and frequency of the KS signal. The PCM uses the KS signal to calculate the average voltage. Then the PCM assigns a voltage value. The PCM checks the KS and related wiring by comparing the actual knock signal to the assigned voltage range. A normal KS signal should stay within the assigned voltage range This Diagnostic Trouble Code (DTC) will set if the KS signal is outside the assigned voltage range or not present. The knock sensor system uses 2 knock sensors. KS 1 is located at the front of the engine, or nearest the accessory belt. KS 2 is located at the rear of the engine, or nearest the driveplate. Both sensors are on the intake side of the block.

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

1. 2 This step verifies a condition is present.
2. 4 This test is checking for continuity in the KS circuit. An out of limit on the Digital Multimeter (DMM) display is indicating an open in either the wiring or the PCM.

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 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 refer to the step numbers on 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-132531-S34626661012002012100000) .
4. 8 An intermittent problem may be caused by a number of conditions. See «DIAGNOSTIC AIDS»(ref-132531-S34626661012002012100000) .
5. 11 Program the replacement PCM and perform the Crankshaft Position System Variation Learn Procedure. See «POWERTRAIN CONTROL MODULE»(ref-132531-S15401290812002012100000) and «CRANKSHAFT POSITION SENSOR»(ref-132531-S34845224152002012100000) 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 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 numbers below refer to the step numbers on the diagnostic procedures.

1. 8 This step determines if there is a problem with the signal circuit.
2. 9 If the fuse is open in the jumper wire, there is a short to ground on the signal circuit.

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.

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

1. 3 This step determines if the DTC P0341 is the result of a hard malfunction or an intermittent condition.
2. 4 The counter should stop incrementing with the sensor electrical connector disconnected and set a DTC P0340. If the counter stills increments, this indicates that the PCM is malfunctioning.
3. 7 A faulty electrical connection in any of the circuits at the CMP sensor will cause the CMP Resync Counter to increment. When a faulty electrical connection is present, the CMP Reference Activity counter will stop incrementing and the CMP Resync Counter will increment.

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 (O2) sensor. 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 O2 sensor 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 numbers below refer to the step numbers on the diagnostic procedures.

1. 3 This table checks for conditions that can cause the three-way catalytic converter efficiency to appear degraded. Inspect and repair exhaust system as necessary.
2. 6 Before the three-way catalytic converter is replaced, make sure that the following conditions are not present: Misfire. High engine oil consumption or coolant consumption. Retarded spark timing or weak spark.

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 refer to the step numbers on the diagnostic procedures.

1. 4 This test verifies that the EVAP purge valve can be commanded ON and OFF.
2. 5 This test verifies that the EVAP vent valve can be commanded ON and OFF.
3. 10 This test verifies that engine vacuum is present when the EVAP purge valve is open.
4. 12 This test verifies that the FTP sensor is accurate. An EVAP 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. 6 This step verifies the repairs that have been made.

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 near 0 in. H2O in a calibrated time, DTC P0446 will set.

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

1. 7 This step checks for a restricted EVAP vent valve.
2. 8 This step checks 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. 5 This step tests for the proper operation of the circuit in the high voltage range.

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 above a predetermined value, DTC P0453 will set.

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

1. 2 If DTC P1635 or P1639 set, the 5-volt reference circuit maybe shorted to voltage.

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

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

The transmission range (TR) switch is part of the park/neutral position and back-up lamp switch assembly and is externally mounted on the transmission manual shaft. The TR switch is a multi-signal switch. The PCM supplies ignition voltage to the TR switch on four signal circuits, A, B, C, and P. Each gear selector lever position grounds one or more of the switch circuits. In order to determine the gear range selected by the driver, the PCM compares the voltage combinations on the signal circuits to a look up table stored in the PCM memory. PCM detects the selected gear range by the state change of the switch input. (Scheme 1) Switch input to the PCM is represented on the scan tool as HI and LOW. HI indicates an ignition voltage signal. LOW indicates a zero voltage signal. The four parameters represent transmission range switch signal A, B, C and Parity. When the PCM detects an invalid TR switch signal combination, then DTC P0705 sets.

Scheme 1

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

1. 5 By disconnecting the TR switch, the ground path of all TR switch circuits would be removed and the PCM would recognize all circuits as open. The scan tool will display HI for all range signals.
2. 6 This step tests TR switch wiring for an open or the lack of the signal voltage from the PCM.
3. 7 This step tests TR switch wiring and the PCM by providing a ground path through a fused jumper wire. When grounded, the scan tool range signal A should change to LOW.
4. 8 This step tests TR switch wiring and the PCM by providing a ground path through a fused jumper wire. When grounded, the scan tool range signal B should change to LOW.
5. 9 This step tests TR switch wiring and the PCM by providing a ground path through a fused jumper wire. When grounded, the scan tool range signal C should change to LOW.

The brake switch indicates brake pedal status to the Powertrain Control Module (PCM). The brake switch is a normally-closed switch that supplies battery voltage on the TCC brake switch signal circuit to the PCM. Applying the brake pedal opens the switch, interrupting voltage to the PCM. When the brake pedal is released, the PCM receives a constant voltage signal. If the PCM receives a zero voltage signal at the brake switch input, and the Torque Converter Clutch (TCC) is engaged, the PCM de-energizes the TCC solenoid valve. The PCM disregards the brake switch input for TCC scheduling if there is a brake switch circuit fault. When the PCM detects an open brake switch circuit, 0 volts, low input, during accelerations, then DTC P0719 sets. DTC P0719 is a type C DTC.

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

1. 3 This step isolates the brake switch as a source for setting the DTC.

The brake switch indicates brake pedal status to the Powertrain Control Module (PCM). The brake switch is a normally-closed switch that supplies battery voltage on the TCC brake switch signal circuit to the PCM. Applying the brake pedal opens the switch, interrupting voltage to the PCM. When the brake pedal is released, the PCM receives a constant voltage signal. If the PCM receives a zero voltage signal at the brake switch input, and the Torque Converter Clutch (TCC) is engaged, the PCM de-energizes the TCC solenoid valve. The PCM disregards the brake switch input for TCC scheduling if there is a brake switch circuit fault. When the PCM detects a closed brake switch circuit, 12 volts, high input, during decelerations, then DTC P0724 sets. DTC P0724 is a type C DTC.

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

1. 2 This step isolates the brake switch as a source for setting the DTC.

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 near the 5-volt reference and decreases as the throttle plate is opened. TP sensor 2 signal voltage at closed throttle is near the low reference and increases as the throttle plate is opened. When TP sensor 1 signal voltage is not within the predicted range, this code sets.

The Powertrain Control Module (PCM) continuously monitors the Heated Oxygen Sensor 1 (HO2S 1) activity for 100 seconds. During the monitoring period, the PCM counts the number of times that the HO2S 1 switches from rich to lean, and from lean to rich. You can determine a total for all of the switches with this information. If the number of switches is too low, a DTC P1133 will set.

In order to control emissions, a catalytic converter converts any harmful exhaust emissions into harmless water vapor and carbon dioxide. The Powertrain Control Module (PCM) can monitor this process by using a rear Heated Oxygen Sensor 2 (HO2S 2). The HO2S 2, located in the exhaust stream past the catalytic converter, produces an output signal which indicates the storage capacity of the catalyst. This signal indicates the catalyst's ability to effectively convert the exhaust emissions. If the catalyst is functioning properly, the HO2S 2 signal will be far less active than the signal produced by the front Heated Oxygen Sensor 1 (HO2S 1). Do not attempt to repair the HO2S 2. Replace the entire HO2S 2 assembly if the following conditions exist

1. Damaged wiring.
2. Damaged electrical connector.
3. Damaged terminals.

Obstruction of the air reference and a degraded HO2S 2 performance can result from any attempt to repair the above conditions. The HO2S 2 must have a clean air reference in order for the HO2S 2 to function properly. This clean air reference is obtained by way of the HO2S 2 wires.

In order to control the emissions, a catalytic converter converts any harmful exhaust emissions into harmless water vapor and carbon dioxide. The Powertrain Control Module (PCM) can monitor this process by using a rear Heated Oxygen Sensor 2 (HO2S 2). The HO2S 2, located in the exhaust stream past the catalytic converter, produces an output signal which indicates the storage capacity of the catalyst. This signal indicates the catalyst's ability to effectively convert the exhaust emissions. If the catalyst is functioning properly, the HO2S 2 signal will be far less active than the signal produced by the front Heated Oxygen Sensor 1 (HO2S 1). Do not attempt to repair the HO2S 2. Replace the entire HO2S 2 assembly if the following conditions exist

1. Damaged wiring.
2. Damaged electrical connectors.
3. Damaged terminals.

Obstruction of the air reference and degraded HO2S 2 performance can result from any attempt to repair the above conditions. The HO2S must have a clean air reference in order for the HO2S 2 to function properly. This clean air reference is obtained by way of the HO2S 2 wires.

The Powertrain Control Module (PCM) internal circuitry can identify if the vehicle fuel system is capable of supplying adequate amounts of fuel during heavy acceleration (power enrichment). When a power enrichment mode of operation is requested during a Closed Loop operation, by heavy acceleration, the PCM provides additional fuel to the engine. Under these conditions the PCM should detect a rich condition. Whenever this rich exhaust is not detected, a DTC P1171 sets. A plugged fuel filter or restricted fuel line can prevent adequate amounts of fuel from being supplied during Power Enrichment Mode.

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

1. 5 This step checks to see if the HO2S 1 is operating properly.

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 near the 5-volt reference and decreases as the throttle plate is opened. TP sensor 2 signal voltage at closed throttle is near the low reference and increases as the throttle plate is opened. When TP sensor 2 signal voltage is not within the predicted range, this code sets.

The throttle actuator control assembly has two 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 0 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 refer to the step numbers on 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 the 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 near the low reference and increases as the pedal is actuated. The APP sensor 2 signal voltage at rest position is near 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 table 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 near the low reference and increases as the pedal is actuated. The APP sensor 2 signal voltage at rest position is near 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 near the low reference and increases as the pedal is actuated. The APP sensor 2 signal voltage at rest position is near the 5-volt reference and decreases as the pedal is actuated. When APP sensor 2 signal voltage is not within the predicted range, this code 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 Diagnostic Trouble Code (DTC) set 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 Diagnostic Trouble Code (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.

Rough roads cause torque on the tires that is transmitted to the powertrain. This slows down the crankshaft giving the appearance of a misfire. The Electronic Brake Control Module (EBCM) determines rough road surfaces using input from the wheel speed sensors. The EBCM then sends the rough road data to the Powertrain Control Module (PCM) on the serial data circuit. The PCM uses the rough road data to enhance the misfire diagnostic. The data allows the PCM to distinguish the crankshaft speed variations caused by rough road surfaces from those caused by true misfires. If the EBCM is unable to identify rough road conditions while the PCM detects a misfire condition, DTC P1380 will set.

Rough roads cause torque on the tires that is transmitted to the powertrain. This slows down the crankshaft giving the appearance of a misfire. The Electronic Brake Control Module (EBCM) determines rough road surfaces using input from the wheel speed sensors. The EBCM then sends the rough road data to the Powertrain Control Module (PCM) via class 2 serial data. The PCM uses the rough road data to enhance the misfire diagnostic. The data allows the PCM to distinguish the crankshaft speed variations caused by rough road surfaces from those caused by true misfires. If a loss of communication occurs that causes the PCM not to receive rough road information while a misfire condition is requesting the Malfunction Indicator Lamp (MIL), DTC P1381 will set.

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

1. 2 Ensures that the EBCM is capable of transmitting serial data on the Class 2 serial data circuit.

This Diagnostic Trouble Code (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 number below refers to the step number in the diagnostic procedures.

1. 4 This test determines if the EVAP canister purge valve can seal. Any indication of vacuum on the vacuum gage indicates that the EVAP purge valve is not seating properly.

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 Diagnostic Trouble Code (DTC) sets if the values are greater than the calibrated range.

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

1. 3 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. 6 When the 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 lamp as the ignition is turned ON.

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

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

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

The numbers below refer to the step numbers on 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 1 individual condition may correct more than 1 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 Diagnostic Trouble Code (DTC) sets if the values are greater than the calibrated range.

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

1. 3 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. 6 When the 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 lamp 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 Diagnostic Trouble Code (DTC) sets if the values are greater than the calibrated range.

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

1. 3 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. 6 When the 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 lamp 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 Diagnostic Trouble Code (DTC) is set.

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

1. 8 More than 1 ETC 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. Keep this in mind when reviewing captured DTC info.

The ignition switch uses an ignition voltage supply separate from the Powertrain Control Module (PCM) supply. If the PCM detects ignition 1 voltage but not ignition 0 voltage, this Diagnostic Trouble Code (DTC) will set.

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

1. The Throttle Position (TP) sensor 1.
2. The Accelerator Pedal Position (APP) sensor 2.
3. The AC pressure sensor.
4. The Fuel Tank Pressure (FTP) sensor.
5. The 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. The Throttle Position (TP) sensor 2.
2. The Accelerator Pedal Position (APP) sensor 1.
3. The 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 electronic throttle control (ETC) system uses an ignition voltage supply separate from the Powertrain Control Module (PCM) supply. If the PCM detects a voltage difference between the two circuits, this Diagnostic Trouble Code (DTC) will set.