Engine Controls - 2.6l & 3.2l - Diagnosis (DTC p0030 - p0174) Cadillac CTS I

Circuit Description

Heating elements inside the heated oxygen sensor (HO2S) minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. A low side driver within the engine control module (ECM) is pulse width controlled to provide current to the heater elements. During warm-up the ECM will pulse the heaters ON-OFF to prevent thermal shock to the sensor components from moisture in the exhaust system. The ECM will not allow continuous HO2S heating until calibrated limits of time, temperature, and intake airflow have been reached. The ECM continuously monitors the HO2S heater current draw and operating state by briefly turning OFF the heater low side driver at regular intervals. A small reference voltage is present at the heater low control circuit. When the low side driver is commanded ON, the reference voltage is low, 2.6-4.6 volts. When the low side driver is commanded OFF, the reference voltage is high, close to battery voltage. If the ECM detects that the HO2S heater low control circuit voltage is between 2.6-4.6 volts when the heater is commanded OFF, DTCs P0030, P0036, P0050, or P0056 will set.

Each HO2S has the following circuits

1. The HO2S high signal circuit
2. The HO2S low signal circuit
3. The HO2S heater ignition 1 voltage circuit
4. The HO2S heater low control circuit

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

The ECM detects that the HO2S heater low control circuit voltage is between 2.6-4.6 volts when the heater is commanded OFF, indicating an open HO2S heater circuit.

Action Taken When the DTC Sets

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

DTC P0030, P0036, P0050, or P0056

Heating elements inside the heated oxygen sensor (HO2S) minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. A low side driver within the engine control module (ECM) is pulse width controlled to provide current to the heater elements. During warm-up the ECM will pulse the heaters ON-OFF to prevent thermal shock to the sensor components from moisture in the exhaust system. The ECM will not allow continuous HO2S heating until calibrated limits of time, temperature, and intake airflow have been reached. The ECM continuously monitors the HO2S heater current draw and operating state by briefly turning OFF the heater low side driver at regular intervals. A small reference voltage is present at the heater low control circuit. When the low side driver is commanded ON, the reference voltage is low, 2.6-4.6 volts. When the low side driver is commanded OFF, the reference voltage is high, close to battery voltage. If the ECM detects that the HO2S heater low control circuit voltage is lower than 2.6 volts when the heater is commanded OFF, DTCs P0031, P0037, P0051, or P0057 will set.

Each HO2S has the following circuits

1. The HO2S high signal circuit
2. The HO2S low signal circuit
3. The HO2S heater ignition 1 voltage circuit
4. The HO2S heater low control circuit

The engine is running.

The ECM detects that the HO2S heater low control circuit voltage is below 2.6 volts when the heater is commanded OFF, indicating a shorted HO2S heater circuit.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

DTC P0031, P0037, P0051, or P0057

Heating elements inside the heated oxygen sensor (HO2S) minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. A low side driver within the engine control module (ECM) is pulse width controlled to provide current to the heater elements. During warm-up the ECM will pulse the heaters ON-OFF to prevent thermal shock to the sensor components from moisture in the exhaust system. The ECM will not allow continuous HO2S heating until calibrated limits of time, temperature, and intake airflow have been reached. The ECM continuously monitors the HO2S heater current draw and operating state by briefly turning OFF the heater low side driver at regular intervals. A small reference voltage is present at the heater low control circuit. When the low side driver is commanded ON, the reference voltage is low, 2.6-4.6 volts. When the low side driver is commanded OFF, the reference voltage is high, close to battery voltage. If the ECM detects that the HO2S heater low control circuit voltage is higher than 4.6 volts when the heater is commanded ON, DTCs P0032, P0038, P0052, or P0058 will set.

Each HO2S has the following circuits

1. The HO2S high signal circuit
2. The HO2S low signal circuit
3. The HO2S heater ignition 1 voltage circuit
4. The HO2S heater low control circuit

The engine is running.

The ECM detects that the HO2S heater low control circuit voltage is above 4.6 volts when the heater is commanded ON, indicating an HO2S heater circuit shorted to voltage.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

DTC P0032, P0038, P0052, or P0058

The mass air flow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The MAF sensor used on this vehicle is a hot film meter (HFM) type. The engine control module (ECM) uses the MAF sensor signal in order to provide the correct fuel delivery for a wide range of engine speeds and loads. The MAF sensor signal is a function of the current required to keep the air flow sensing element at a fixed temperature. The air flowing through the sensor cools the sensing element. The amount of cooling is proportional to the amount of the air flow. As the air flow increases, more current is required in order to maintain the hot film at a constant temperature. The MAF sensor converts the changes in current to a voltage signal that is read by the ECM. The ECM calculates the air flow based on this voltage signal. The MAF sensor uses the following circuits in order to operate

1. The ignition 1 voltage
2. The 5-volt reference
3. The MAF sensor signal
4. The low reference

The 5-volt reference for the MAF sensor is also supplied to additional sensors. For each of the sensors the voltage is supplied on separate ECM terminals. The terminals are connected within the ECM to the same stabilized sensor supply voltage. The 5-volt reference is shared by the following sensors

1. The MAF sensor
2. The accelerator pedal position (APP) sensor 1
3. The fuel tank pressure (FTP) sensor
4. The air conditioning (A/C) pressure sensor

The low reference circuit of the MAF sensor is shared with the following components

1. The camshaft position (CMP) sensor
2. The intake air temperature (IAT) sensor
3. The engine coolant temperature (ECT) sensor

The ECM compares the actual MAF sensor voltage signal to the predicted MAF value. The predicted MAF value is based on engine speed and throttle valve opening. This comparison will determine if the signal is stuck based on a lack of variation, or is too low or too high for a given operating condition. If the ECM detects that the actual MAF sensor signal is not within a predetermined range of the predicted MAF value, DTC P0101 sets.

1. The ECM has counted more than 20 crankshaft revolutions.
2. The engine speed is more than 300 RPM.
3. The engine has been running for more than 0.5 seconds in order to allow the MAF sensor hot film element to heat up.
4. The ignition 1 signal is more than 10 volts.

The ECM detects that the actual MAF sensor signal is not within a predetermined range of the predicted MAF value for more than 2 seconds.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

1. Inspect for the following conditions: A low minimum air rate through the sensor bore may cause this DTC to set at idle or during deceleration. Inspect for any vacuum leaks downstream of the MAF sensor. Any contamination of the hot film element of the MAF sensor may cause this DTC to set. A skewed or stuck throttle position (TP) sensor 1 or TP sensor 2 may cause this DTC to set. A wide-open throttle acceleration from a stop should cause the MAF sensor g/s display on the scan tool to increase rapidly. This increase should be from 3-7 g/s at idle to 72 g/s or more at the time of the 1-2 shift. If the increase is not observed, inspect for a restriction in the induction system or the exhaust system.
2. If the condition is intermittent, refer to «Intermittent Conditions»(/cadillac/cts/i-2002-2007/remont/testing-diagnostics/#engine-controls-26l-32l-troubleshooting__intermittent-conditions) .

Test Description

The numbers below refer to the step numbers on the diagnostic table

1. 4: This step will determine if the MAF sensor voltage is less than the proper range at idle.
2. 5: This step will determine if the MAF sensor voltage is more than the proper range at idle.
3. 6: This step will determine if the throttle position (TP) sensors are operating properly.
4. 7: This step will determine if any mechanical faults have caused this DTC to set.

DTC P0101

The mass air flow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The MAF sensor used on this vehicle is a hot film meter (HFM) type. The engine control module (ECM) uses the MAF sensor signal in order to provide the correct fuel delivery for a wide range of engine speeds and loads. The MAF sensor signal is a function of the current required to keep the air flow sensing element at a fixed temperature. The air flowing through the sensor cools the sensing element. The amount of cooling is proportional to the amount of the air flow. As the air flow increases, more current is required in order to maintain the hot film at a constant temperature. The MAF sensor converts the changes in current to a voltage signal that is read by the ECM. The ECM calculates the air flow based on this voltage signal. The MAF sensor uses the following circuits in order to operate

1. The ignition 1 voltage
2. The 5-volt reference
3. The MAF sensor signal
4. The low reference

The 5-volt reference for the MAF sensor is also supplied to additional sensors. For each of the sensors, the voltage is supplied on separate ECM terminals. The terminals are connected within the ECM to the same stabilized sensor supply voltage. The 5-volt reference is shared by the following sensors

1. The MAF sensor
2. The accelerator pedal position (APP) sensor 1
3. The fuel tank pressure (FTP) sensor
4. The air conditioning (A/C) refrigerant pressure sensor

The low reference circuit of the MAF sensor is shared with the following components

1. The camshaft position (CMP) sensor
2. The intake air temperature (IAT) sensor
3. The engine coolant temperature (ECT) sensor

If the ECM detects the MAF sensor signal is less than the possible range of a properly operating sensor, DTC P0102 sets.

1. The ECM has counted more than 20 crankshaft revolutions.
2. The engine speed is more than 300 RPM.
3. The engine has been running for more than 0.5 seconds in order to allow the MAF sensor hot film element to heat up.
4. The ignition 1 signal is more than 10 volts.

1. The ECM detects that the MAF sensor signal is less than 0.42 volt for more than 2 seconds. OR
2. The MAF sensor signal is less than a calculated value using throttle position (TP) and engine speed.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

1. Inspect for the following conditions: A high resistance on any of the MAF sensor circuits except the low reference may cause this DTC to set intermittently and also result in poor engine performance. A high resistance on the 5-volt reference of the MAF sensor may result in poor engine performance without setting this DTC. A low minimum air rate through the sensor bore may cause this DTC to set at idle or during deceleration. Inspect for any vacuum leaks downstream of the MAF sensor. Any contamination of the hot film element of the MAF sensor may cause this DTC to set. A wide-open throttle acceleration from a stop should cause the MAF sensor g/s display on the scan tool to increase rapidly. This increase should be from 3-7 g/s at idle to 72 g/s or more at the time of the 1-2 shift. If the increase is not observed, inspect for a restriction in the Induction System or the Exhaust System.
2. If the condition is intermittent, refer to «Intermittent Conditions»(/cadillac/cts/i-2002-2007/remont/testing-diagnostics/#engine-controls-26l-32l-troubleshooting__intermittent-conditions) .

DTC P0102

The mass air flow (MAF) sensor is an air flow meter that measures the amount of air entering the engine. The MAF sensor used on this vehicle is a hot film meter (HFM) type. The engine control module (ECM) uses the MAF sensor signal in order to provide the correct fuel delivery for a wide range of engine speeds and loads. The MAF sensor signal is a function of the current required to keep the air flow sensing element at a fixed temperature. The air flowing through the sensor cools the sensing element. The amount of cooling is proportional to the amount of the air flow. As the air flow increases, more current is required in order to maintain the hot film at a constant temperature. The MAF sensor converts the changes in current to a voltage signal that is read by the ECM. The ECM calculates the air flow based on this voltage signal. The MAF sensor uses the following circuits in order to operate

1. The ignition 1 voltage
2. The 5-volt reference
3. The MAF sensor signal
4. The low reference

The 5-volt reference for the MAF sensor is also supplied to additional sensors. For each of the sensors the voltage is supplied on separate ECM terminals. The 5-volt reference is shared by the following sensors

1. The MAF sensor
2. The accelerator pedal position (APP) sensor 1
3. The fuel tank pressure (FTP) sensor
4. The air conditioning (A/C) refrigerant pressure sensor

The low reference circuit of the MAF sensor is shared with the following components

1. The camshaft position (CMP) sensor
2. The intake air temperature (IAT) sensor
3. The engine coolant temperature (ECT) sensor

If the ECM detects the MAF sensor signal is more than the possible range of a properly operating sensor DTC P0103 sets.

1. The ECM has counted more than 20 crankshaft revolutions.
2. The engine speed is more than 300 RPM.
3. The engine has been running for more than 0.5 second in order to allow the MAF sensor hot film element to heat up.
4. The ignition 1 signal is more than 10 volts.

1. The ECM detects that the MAF sensor signal is more than 4.88 volts for more than 2 seconds. OR
2. The MAF sensor signal is more than a calculated value using throttle position (TP) and engine speed.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

1. Inspect for the following conditions: A high resistance on the low reference circuit of the MAF sensor may cause this DTC to set intermittently and also result in poor engine performance. An intermittent short to voltage on the low reference circuit of the MAF sensor may cause this DTC to set. It may also result in possible internal ECM damage. Any water in the air induction system may cause this DTC to set. Any contamination of the hot film element of the MAF sensor may cause this DTC to set.
2. If the condition is intermittent, refer to «Intermittent Conditions»(/cadillac/cts/i-2002-2007/remont/testing-diagnostics/#engine-controls-26l-32l-troubleshooting__intermittent-conditions) .

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

1. 4: This step will determine if any mechanical faults have caused this DTC to set.
2. 6: A very small amount of voltage will appear on this circuit when the ECM is operational. This is considered normal.
3. 7: The measured resistance of the circuit will increase when the ECM is operational. This is considered normal.

DTC P0103

The intake air temperature (IAT) sensor is a variable resistor. The IAT sensor has a signal circuit and a low reference circuit. The IAT sensor measures the temperature of the air entering the engine. The engine control module (ECM) supplies 5 volts to the IAT signal circuit, and a ground for the IAT low reference circuit. When the IAT sensor is cold, the sensor resistance is high. When the air temperature increases, the sensor resistance decreases. With high sensor resistance, the ECM detects a high voltage on the IAT signal circuit. With lower sensor resistance, the ECM detects a lower voltage on the IAT signal circuit. If the ECM detects an excessively low IAT signal voltage, indicating a high temperature, DTC P0112 sets.

1. The engine is running for more than 1 minute and 20 seconds.
2. The engine has been idling for more than 10 seconds.

The IAT sensor parameter is more than 139°C (282°F) for more than 2 seconds.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

DTC P0112

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

1. The engine is running for more than 1 minute and 20 seconds.
2. The engine has been idling for more than 10 seconds.

The IAT sensor parameter is less than -39°C (-38°F) for more than 2 seconds.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

The number below refer to the step number on the diagnostic table.

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

DTC P0113

An engine coolant temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the engine control module (ECM) for engine control and as an enabling criteria for some diagnostics.

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

This DTC will run continuously. The ECM calculates a modeled temperature using startup ECT, mass air flow (MAF), intake air temperature (IAT) and engine speed.

If the ECM detects the calibrated amount of air flow and engine run time at any time is equal to a predetermined value, and the engine coolant is not within range of the calibrated temperature, DTC P0116 sets.

1. DTCs P0112, P0113, P0117, P0118, P0125, or P0128 are not set.
2. The engine run time is more than 8 minutes.

1. The calibrated amount of air flow at any time has been met.
2. The calibrated amount of engine run time at any time has been met.
3. The actual ECT is 20°C (36°F) more than a predetermined calibrated ECT.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

DTC P0116

The engine coolant temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The engine control module (ECM) supplies 5 volts to the ECT signal circuit, and a ground for the ECT low reference circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance decreases. With high sensor resistance, the ECM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the ECM detects a lower voltage on the ECT signal circuit. If the ECM detects an excessively low ECT signal voltage, which is a high temperature indication, DTC P0117 sets.

The ignition is ON.

OR

The engine is cranking or running.

The ECT sensor parameter is more than 138°C (280°F) for more than 0.3 seconds.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

DTC P0117

The engine coolant temperature (ECT) sensor is a variable resistor, that measures the temperature of the engine coolant. The ECT sensor has a signal circuit and a low reference circuit. The engine control module (ECM) supplies 5 volts to the ECT signal circuit, and a ground for the ECT low reference circuit. When the ECT is cold, the sensor resistance is high. When the ECT increases, the sensor resistance decreases. With high sensor resistance, the ECM detects a high voltage on the ECT signal circuit. With lower sensor resistance, the ECM detects a lower voltage on the ECT signal circuit. If the ECM detects an excessively high ECT signal voltage, which is a low temperature indication, DTC P0118 sets.

The ignition is ON.

OR

The engine is cranking or running.

The ECT sensor parameter is less than -39°C (-38°F) for more than 0.3 seconds.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

The number below refers to the step number on the diagnostic table.

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

DTC P0118

The throttle position (TP) sensors 1 and 2 are located within the throttle body assembly. The TP sensors share a common 5-volt reference circuit and a common low reference circuit. The 5-volt reference circuit is also shared with accelerator pedal position (APP) sensor 2. The 5-volt reference voltage is supplied on 2 separate engine control module (ECM) terminals, but the terminals are connected internally to the same voltage supply. Each TP sensor has an individual signal circuit which provides the ECM with a signal voltage proportional to the throttle plate movement. When the throttle plate is in the closed position, the TP sensor 1 signal voltage is near the low reference and increases as the throttle plate is opened. TP sensor 2 signal voltage at closed throttle is near the 5-volt reference and decreases as the throttle plate is opened. The ECM compares the signal of the TP sensors to the mass air flow (MAF) sensor when the engine is running to determine if the sensor readings are correct. The control module also compares the signal of TP sensor 1 and TP sensor 2 through the entire range. If the ECM detects a difference of more than 6 percent between sensor 1 and sensor 2, and a difference from the predicted range by more than 9 percent, DTC P0121 sets.

1. The battery voltage is more than 10 volts.
2. The TP voltage is more than 0.17 volts and less than 4.6 volts.

1. The TP sensor 1 disagrees more than 6 percent from TP sensor 2.
2. The TP sensor 1 disagrees more than 9 percent from the predicted value.
3. The above conditions are met for 280 milliseconds.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

DTC P0121

The throttle position (TP) sensors 1 is used to determine the throttle plate angle by the engine control module (ECM) for various engine management systems. The TP sensor is a potentiometer type sensor with the following three circuits

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

The ECM provides the TP sensor with a 5-volt reference circuit and a low reference circuit. The TP sensor then provides the PCM with a signal voltage proportional to throttle plate movement. The TP sensor 1 signal voltage at closed throttle is low and increases as the throttle is opened. When the ECM detects the TP sensor 1 voltage is less than 0.195 volts, DTC P0122 sets.

1. The battery voltage is more than 10 volts.
2. The ignition is ON.

The TP sensor 1 voltage is less than 0.195 volt for more than 140 milliseconds.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

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

1. 4: The ECM performs a comparison of the signals from both throttle position sensors during the entire range of operation. If the DTC does not set with the key ON and the accelerator pedal released, actuating the throttle may cause the DTC to set.
2. 6: This step tests for the proper operation of the TP sensor 1 signal circuit. The ECM supplies a pull up voltage of about 4.8 volts on the signal circuit.
3. 7: This step is to test the integrity of the low reference circuit through the ECM.
4. 10: The 5-volt reference for the TP sensors and the accelerator pedal position (APP) sensor 2 are connected inside the ECM. This step is to determine if the APP sensor is affecting the 5-volt reference circuit of the TP sensors.

DTC P0122

The throttle position (TP) sensors 1 and 2 are located within the throttle body assembly. The TP sensors share a common 5-volt reference circuit and a common low reference circuit. The 5-volt reference circuit is also shared with the accelerator pedal position (APP) sensor. The 5-volt reference voltage is supplied on 2 separate engine control module (ECM) terminals, but the terminals are connected internally to the same voltage supply. Each TP sensor has an individual signal circuit which provides the ECM with a signal voltage proportional to throttle the plate movement. When the throttle plate is in the closed position, the TP sensor 1 signal voltage is near the low reference and increases as the throttle plate is opened. TP sensor 2 signal voltage at closed throttle is near the 5-volt reference and decreases as the throttle plate is opened. If the ECM detects the TP sensor 1 signal voltage is less than 4.6 volts DTC P0123 sets.

1. The battery voltage is more than 10 volts.
2. The ignition is ON.

The TP sensor 1 voltage is more than 4.6 volts for more than 140 milliseconds.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

DTC P0123

An engine coolant temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the engine control module (ECM) for engine control and as an enabling criteria for some diagnostics.

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

This DTC will run continuously.

If the ECM detects the calibrated amount of air flow and engine run time at any time have been met, and the engine coolant has not met the Closed Loop temperature, DTC P0125 sets.

1. The engine is running.
2. A block heater is not detected or the DTC will be delayed for 25 seconds.

1. The calibrated amount of air flow at any time has been met.
2. The calibrated amount of engine run time at any time has been met.
3. The minimum ECT for Closed Loop is 20.25°C (68.45°F) less than a predetermined calibrated temperature.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

DTC P0125

An engine coolant temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the engine control module (ECM) 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 ECT as enabling criteria may not run when expected.

This DTC will run continuously. If the ECM detects the calibrated amount of air flow and engine run time at any time is equal to a predetermined value, and the ECT has not met the minimum calibrated thermostat regulating temperature, DTC P0128 sets.

1. DTCs P0116, P0117, P0118, P0125, or P0500 are not set.
2. The startup ECT is less than 50.25°C (122.45°F).
3. The start-up intake air temperature (IAT) is between -9.75 and +50.25°C (+14.45 to +122.45°F).
4. Fuel cutoff is not active.
5. The engine is running at more than 960 RPM.
6. The vehicle is moving at more than 15 km/h (9 mph).
7. More than 3 kg of air has passed through the engine.
8. A block heater is not detected or the DTC is delayed for 25 seconds.

The PCM detects that

1. The calibrated amount of engine run time at any time has been met
2. The calibrated amount of engine air flow at any time has been met
3. The actual ECT is 11°C (19°F) less than a predetermined calibrated ECT should be.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

DTC P0128

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 of the exhaust stream. When the vehicle is first started the engine control module (ECM) operates in an open loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The ECM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage once the sensor reaches operating temperature. High HO2S voltage output indicates a rich fuel mixture; low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. If the ECM detects an active HO2S voltage signal below a calibrated minimum amplitude, DTCs P0130, P0136, P0150, or P0156 will set.

Each HO2S has the following circuits

1. The HO2S high signal circuit
2. The HO2S low signal circuit
3. The HO2S heater ignition 1 voltage circuit
4. The HO2S heater low control circuit

1. DTCs P0443, P0444, or P0445 are not set.
2. The engine is running.
3. The Calc Convertor Temp parameter is less than 800°C (1,472°F).
4. The MAF parameter is between 10-35 g/s.
5. The TP Angle parameter is between 5-35 percent.
6. The Battery Voltage parameter is more than 10.5 volts.

1. The ECM detects that the affected HO2S 1 voltage is between 60-400 mV, when the same bank HO2S 2 voltage is above 499 mV for at least 10 seconds. OR
2. The ECM detects that the affected HO2S 1 voltage is 600-1080 mV, when the same bank HO2S 2 voltage is below 104 mV for at least 10 seconds. OR
3. The ECM detects that the affected HO2S 1 voltage has risen 16 times out of 24 samples when the heater is cycled OFF.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

DTC P0130, P0136, P0150, or P0156

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 of the exhaust stream. When the vehicle is first started the engine control module (ECM) operates in an open loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The ECM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage once the sensor reaches operating temperature. High HO2S voltage output indicates a rich fuel mixture, low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. If the ECM detects an HO2S signal below a calibrated minimum, DTCs P0131, P0137, P0151, or P0157 will set.

Each HO2S has the following circuits

1. The HO2S high signal circuit
2. The HO2S low signal circuit
3. The HO2S heater ignition 1 voltage circuit
4. The HO2S heater low control circuit

Conditions for Running the DTC (Front Sensors)

1. DTCs P0443, P0444, or P0445 are not set.
2. The engine is running.
3. The Calc Converter Temp parameter is less than 800°C (1,472°F).
4. The Battery Voltage is more than 10.5 volts.

Conditions for Running the DTC (Rear Sensors)

1. DTCs P0030, P0031, P0032, P0036, P0037, P0038, P0135, P0155, P0171, P0172, P0174, P0175, P0300, P0301-P0306, P0341, P0342, P0343, P0443, P0444, or P0445 are not set.
2. The Calc Converter Temp parameter is less than 800°C (1,472°F).
3. The MAF parameter is more than 9.72 g/s.
4. The Battery Voltage parameter is more than 10.5 volts.

The DTC will set if the ECM detects an HO2S 1 with a signal voltage below 40 mV and the same bank HO2S 2 with a voltage above 499 mV. The condition must be present for more than 10 seconds for the front sensors, or 680 seconds for the rear sensors.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

DTC P0131, P0137, P0151, or P0157

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 of the exhaust stream. When the vehicle is first started the engine control module (ECM) operates in an open loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The ECM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage once the sensor reaches operating temperature. High HO2S voltage output indicates a rich fuel mixture; low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. The ECM monitors the rich-to-lean and lean-to-rich transition time. If the ECM detects an HO2S 1 voltage signal above a calibrated maximum, DTCs P0132 or P0152 will set.

Each HO2S has the following circuits

1. The HO2S high signal circuit
2. The HO2S low signal circuit
3. The HO2S heater ignition 1 voltage circuit
4. The HO2S heater low control circuit

1. The engine is running.
2. The Calc Converter Temp parameter is less than 800°C (1,472°F).
3. The Battery Voltage parameter is more than 10.5 volts.

The ECM detects an HO2S 1 with a signal voltage above 1,080 mV for more than 5 seconds.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

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

1. 9: This test verifies whether or not the affected HO2S is internally shorted to voltage prior to replacing the ECM.
2. 14: Both components must be replaced since the shorted HO2S has damaged the ECM low reference circuit.

DTC P0132 or P0152

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 of the exhaust stream. When the vehicle is first started the engine control module (ECM) operates in an open loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The ECM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage once the sensor reaches operating temperature. High HO2S voltage output indicates a rich fuel mixture; low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. The ECM monitors the rich-to-lean and lean-to-rich transition time. If the ECM detects an HO2S 1 voltage signal average transition time that is too slow, DTCs P0133, or P0153 will set.

Each HO2S has the following circuits

1. The HO2S high signal circuit
2. The HO2S low signal circuit
3. The HO2S heater ignition 1 voltage circuit
4. The HO2S heater low control circuit

1. DTCs P0030, P0031, P0032, P0036, P0037, P0038, P0101, P0102, P0103, P0112, P0113, P0116, P0117, P0118, P0125, P0128, P0135, P0141, P0171, P0172, P0174, P0175, P0300, P0301-P0306, P0443, P0444, and P0445 are not set.
2. The Loop Status Bank 1 and Loop Status Bank 2 parameter is closed.
3. The Engine Speed parameter is between 1,200-3,000 RPM.
4. The Calc Converter Temp parameter is over 350°C (662°F).
5. The Volumetric Efficiency parameter is between 12-70 percent.
6. The purge solenoid valve has been commanded OFF for at least 10 seconds.
7. This diagnostic runs once per ignition cycle once the above conditions are met.

The ECM detects that the HO2S 1 signal takes longer than 1 second to switch, after 12 valid switching cycles have occurred.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

DTC P0133 or P0153

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 of the exhaust stream. When the vehicle is first started the engine control module (ECM) operates in an open loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The ECM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage once the sensor reaches operating temperature. High HO2S voltage output indicates a rich fuel mixture; low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. The ECM monitors the rich-to-lean and lean-to-rich transition time. If the ECM detects an HO2S 1 voltage signal that remains at or near the bias voltage, DTCs P0134 or P0154 will set.

Each HO2S has the following circuits

1. The HO2S high signal circuit
2. The HO2S low signal circuit
3. The HO2S heater ignition 1 voltage circuit
4. The HO2S heater low control circuit

1. The engine is running.
2. The Calc Converter Temp parameter is less than 800°C (1,472°F).
3. The Battery Voltage parameter is more than 10.5 volts.

1. The ECM detects no affected HO2S 1 sensor activity, and the affected HO2S 1 voltage is between 400-597 mV for more than 7 seconds. OR
2. The ECM detects that both of the affected front and rear HO2S voltage signals remain above 200 mV during Decel Fuel Cutoff, for more than 3 seconds. OR
3. The ECM detects the affected HO2S 1 internal resistance is more than 20,000 ohms.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

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

1. 10: This test verifies whether or not the affected HO2S is internally shorted to voltage prior to replacing the ECM.
2. 15: Both components must be replaced since the shorted HO2S has damaged the ECM low reference circuit.

DTC P0134 or P0154

Heating elements inside the heated oxygen sensor (HO2S) minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. A low side driver within the engine control module (ECM) is pulse width controlled to provide current to the heater elements. During warm-up the ECM will pulse the heaters ON-OFF to prevent thermal shock to the sensor components from moisture in the exhaust system. The ECM will not allow continuous HO2S heating until calibrated limits of time, temperature, and intake airflow have been reached. The ECM continuously monitors the HO2S heater current draw and operating state by briefly turning OFF the heater low side driver at regular intervals. A small reference voltage is present at the heater low control circuit. When the low side driver is commanded ON, the reference voltage is low, 2.6-4.6 volts. When the low side driver is commanded OFF, the reference voltage is high, close to battery voltage. The ECM calculates the HO2S heater element resistance based on the actual heater current. If the ECM detects that the HO2S heater element resistance is too high, DTCs P0135, P0141, P0155, or P0161 will set.

Each HO2S has the following circuits

1. The HO2S high signal circuit
2. The HO2S low signal circuit
3. The HO2S heater ignition 1 voltage circuit
4. The HO2S heater low control circuit

1. DTCs P0030, P0031, P0032, P0036, P0037, P0038, P0050, P0051, P0052, P0056, P0057, P0058, P0157, P0158, P0160, or P0161 are not set.
2. The engine is running.
3. The Calc Converter Temp parameter is between 330-600°C (626-1,112°F).
4. The Battery Voltage parameter is between 10.5-16 volts.

The ECM detects that the affected HO2S Heater Current is not within the expected range, when the HO2S heater is commanded ON.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

The number below refers to the step number on the diagnostic table.

1. 4: This test must not be performed until the HO2S heater has cooled and stabilized for at least 15 minutes. Heater resistance is typically about 10 ohms at room temperature.

DTC P0135, P0141, P0155, or P0161

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 of the exhaust stream. When the vehicle is first started the engine control module (ECM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The ECM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage once the sensor reaches operating temperature. High HO2S voltage output indicates a rich fuel mixture, low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. The ECM monitors the rich-to-lean and lean-to-rich transition time. If the ECM detects an HO2S 2 voltage signal that remains above a calibrated voltage, DTCs P0138 or P0158 will set.

Each HO2S has the following circuits

1. The HO2S high signal circuit
2. The HO2S low signal circuit
3. The HO2S heater ignition 1 voltage circuit
4. The HO2S heater low control circuit

1. The engine is running.
2. The Calc Converter Temp parameter is less than 800°C (1,472°F).
3. The Battery Voltage parameter is more than 10.5 volts.

The ECM detects that the affected HO2S 2 voltage remains over 1,080 mV for more than 5 seconds.

OR

The ECM detects that the affected HO2S 2 voltage signal remains above 200 mV during decel fuel cut-off (DFCO), for more than 3 seconds.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

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

1. 10: This test verifies whether or not the affected HO2S is internally shorted to voltage prior to replacing the ECM.
2. 15: Both components must be replaced since the shorted HO2S has damaged the ECM low reference circuit.

DTC P0138 or P0158

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 of the exhaust stream. When the vehicle is first started the engine control module (ECM) operates in an open loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The ECM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage once the sensor reaches operating temperature. High HO2S voltage output indicates a rich fuel mixture; low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. The ECM monitors the rich-to-lean and lean-to-rich transition time. If the ECM detects an HO2S 2 voltage signal that remains at or near the bias voltage, DTCs P0140 or P0160 will set.

Each HO2S has the following circuits

1. The HO2S high signal circuit
2. The HO2S low signal circuit
3. The HO2S heater ignition 1 voltage circuit
4. The HO2S heater low control circuit

1. The engine is running.
2. The Calc Converter Temp parameter is less than 800°C (1,472°F).
3. The Battery Voltage parameter is more than 10.5 volts.

1. The ECM detects no affected HO2S 2 sensor activity, and the affected HO2S 2 voltage is between 400-520 mV for more than 600 seconds. OR
2. The ECM detects that the affected HO2S 2 internal resistance is more than 40,000 ohms.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

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

1. 9: This test verifies whether or not the affected HO2S is internally shorted to voltage prior to replacing the ECM.
2. 14: Both components must be replaced since the shorted HO2S has damaged the ECM low reference circuit.

DTC P0140 or P0160

The engine control module (ECM) 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 ECM determines fuel delivery based on sensor signals, without oxygen sensor input. During Closed Loop the ECM adds oxygen sensor inputs to calculate fuel trim. If the oxygen sensors indicate a lean condition, fuel trim values will be above 0 percent. If the oxygen sensors indicate a rich condition, fuel trim values will be below 0 percent. Short Term Fuel Trim (FT) values change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. Long Term FT values change slower in response to trends in Short Term FT adjustments. This DTC is continuously monitored during engine operation. If the ECM detects an excessively lean condition, DTC P0171 or P0174 sets.

1. DTCs P0101, P0102, P0103, P0130, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141 are not set.
2. The system is in Closed Loop status.
3. Fuel trim is enabled.
4. The fuel level is more than 10 percent.

1. The LT FT Cruise/Acce parameter is above 23 percent. OR
2. The LT FT Idle/Decel. parameter is above 8.5 percent.

1. The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

1. The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
2. A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
3. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
4. Clear the MIL and the DTC with a scan tool.

1. A skewed mass air flow (MAF) sensor may set this DTC. Refer to «DTC P0101»(/cadillac/cts/i-2002-2007/remont/testing-diagnostics/#engine-controls-26l-32l-diagnosis-dtc-p0030-p0174) .
2. The system will go lean if an injector is not suppling enough fuel.
3. The system will go lean during high fuel demand.
4. Review the Failure Records with a scan tool. If an intermittent condition is suspected, refer to «Intermittent Conditions»(/cadillac/cts/i-2002-2007/remont/testing-diagnostics/#engine-controls-26l-32l-troubleshooting__intermittent-conditions) .

DTC P0171 or P0174

See also:
• Engine Controls Schematics
• Engine Controls Connector End Views
• Engine Control Module (ECM) Connector End Views
• Diagnostic System Check - Engine Controls
• Intermittent Conditions
• Circuit Testing
• Wiring Repairs
• Heated Oxygen Sensor (HO2S) Wiring Repairs
• Testing for Intermittent Conditions and Poor Connections
• Connector Repairs
• Engine Control Module (ECM) Replacement
• Diagnostic Trouble Code (DTC) List
• Scan Tool Data List
• Restricted Exhaust
• Testing for Short to Ground
• Draining and Filling Cooling System (LA3, LY9)
• Thermostat Diagnosis (LY7)
• Thermostat Diagnosis (LS6)
• Engine Coolant Temperature (ECT) Sensor Replacement
• Temperature vs Resistance - Engine Coolant Temperature (ECT) Sensor
• Inspection/Maintenance (I/M) Evaporative Emission (EVAP) System Set Procedure
• Exhaust Leakage
• Crankcase Ventilation System Inspection/Diagnosis
• DTC P0102