DTC P0138 or P0158 w/Case Grounded HO2S
Circuit Description
This diagnostic applies only to vehicles built with case grounded heated oxygen sensors (HO2S). To identify the HO2S, refer to Engine Controls Component Views .
The powertrain control module (PCM) supplies a voltage of about 450 mV between the HO2S high and low signal circuits. The oxygen sensor varies the voltage over a range from about 1,000 mV when the exhaust is rich, down through about 10 mV when the exhaust is lean.
The PCM monitors and stores the HO2S voltage information. The PCM evaluates the HO2S voltage samples in order to determine the amount of time the HO2S voltage was out of range. The PCM compares the stored HO2S voltage samples taken within each sample period and determines if the majority of the samples are out of the operating range.
The PCM monitors the HO2S voltage for being fixed above a predetermined voltage. If the PCM detects the voltage is above a predetermined voltage, a diagnostic trouble code (DTC) sets.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1120, P1125, P1220, P1221, P1258, P1404, P1441, P1514, P1515, P1516, P1517, or P1518 are not set. |
| • | The vehicle is operating in Closed Loop. |
| • | The ignition 1 signal is between 9-18 volts. |
| • | The fuel tank level remaining is more than 10 percent. |
| • | Intrusive tests are not in progress. |
| • | The scan tool output controls are not active. |
Rich Test Enable:
| • | The air fuel ratio is between 14.5:1-14.7:1. |
| • | For vehicles with throttle-actuated control (TAC), the throttle position (TP) indicated angle is between 3-70 percent more than the value observed at idle. |
| • | For vehicles without TAC, the TP is between 3-70 percent. |
Decel Fuel Cut-off Test Enable:
| • | Decel fuel cut-off (DFCO) is active. |
| • | The above condition is met for 3 second. |
Conditions for Setting the DTC
Rich Test
The HO2S voltage is more than 930 mV for 200 seconds.
Decel Fuel Cut-off Test
The HO2S voltage is more than 480 mV for 5 seconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | 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
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.
| • | Inspect the HO2S electrical connections for evidence of water intrusion. Water present in the connector causes the B+ supply to the heater to bleed over to the signal circuit. |
| • | Fuel pressure--The system goes rich if the pressure is too high. The PCM compensates for some increase. However, if the fuel pressure is too high, a DTC may set. Refer to Fuel System Diagnosis . |
| • | Rich injectors--Perform the Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2 or Fuel Injector Balance Test with Special Tool . |
| • | Leaking injector--Refer to the Fuel System Diagnosis . Refer to Fuel Injector Balance Test with Tech 2 or Fuel Injector Balance Test with Special Tool . |
| • | Fuel pressure regulator--Inspect the vacuum line going to the fuel pressure regulator for evidence of fuel. Refer to the Fuel System Diagnosis . |
| • | Evaporative emissions (EVAP) canister purge--Check the canister for fuel saturation. If full of fuel, check the canister control and hoses. Refer to Evaporative Emission Control System Description . |
| • | Mass air flow (MAF) sensor --Disconnect the MAF sensor and see if the rich condition is corrected. If so, check for proper installation. If installed correctly, replace the MAF sensor. If the MAF sensor is installed backwards, the system goes rich. The plastic portion of the sensor has arrows in the casting indicating proper air flow direction. The arrows must point toward the engine. |
| • | An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provides the supply of oxygen. Inspect the HO2S wires and connections for breaks or contamination. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems. |
| • | Throttle position (TP) sensor--An intermittent TP sensor output causes the system to go rich, due to a false indication of the engine accelerating. For an intermittent condition, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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If the voltage is above the specified value the condition is present.
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Jumpering the HO2S low signal circuit to ground is necessary for the PCM to correctly measure the voltage on the HO2S high signal circuit. If the HO2S voltage is within the specified range, the PCM and HO2S high signal circuit are OK.
Step | Action | Value(s) | Yes | No | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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Important: This diagnostic applies only to vehicles built with case grounded HO2S. To identify the HO2S, refer to Engine Controls Component Views . Schematic Reference: Engine Controls Schematics | ||||||||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||||||
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Important: With the engine running, observe the front HO2S voltage using a scan tool. If the front HO2S voltage is fixed below 200 mV, refer to DTC P0131 or P0151 .
Is the HO2S voltage more than the specified value? | 930 mV | Go to Step 5 | Go to Step 3 | |||||||||||||||
3 |
Is the HO2S voltage within the specified range? | 350-550 mV | Go to DTC P0140 or P0160 | Go to Step 4 | ||||||||||||||
4 |
Does the DTC fail this ignition? | -- | Go to Step 5 | Go to Diagnostic Aids | ||||||||||||||
Is the HO2S voltage within the specified range? | 350-550 mV | Go to Step 6 | Go to Step 7 | |||||||||||||||
6 |
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 8 | ||||||||||||||
7 |
Important: The sensor may be damaged if the circuit is shorted to a voltage source. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 | ||||||||||||||
8 | Inspect for poor connections at the harness connector of the HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10 | ||||||||||||||
9 | Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 | ||||||||||||||
10 | Replace the affected HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||||||||||
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||||||||||
12 |
Does the DTC run and pass? | -- | Go to Step 13 | Go to Step 3 | ||||||||||||||
13 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||||||||
DTC P0138 or P0158 w/Isolated Grounded HO2S
Circuit Description
This diagnostic applies only to vehicles built with isolated grounded heated oxygen sensors (HO2S). To identify the HO2S, refer to Engine Controls Component Views .
The powertrain control module (PCM) supplies a voltage of about 450 mV between the HO2S high and low signal circuits. The oxygen sensor varies the voltage over a range from about 1,000 mV when the exhaust is rich, down through about 10 mV when the exhaust is lean.
The PCM monitors and stores the HO2S voltage information. The PCM evaluates the HO2S voltage samples in order to determine the amount of time the HO2S voltage was out of range. The PCM compares the stored HO2S voltage samples taken within each sample period and determines if the majority of the samples are out of the operating range.
The PCM monitors the HO2S voltage for being fixed above a predetermined voltage. If the PCM detects the voltage is above a predetermined voltage, a diagnostic trouble code (DTC) sets.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1120, P1125, P1220, P1221, P1258, P1404, P1441, P1514, P1515, P1516, P1517, or P1518 are not set. |
| • | The vehicle is operating in Closed Loop. |
| • | The ignition 1 signal is between 9-18 volts. |
| • | The fuel tank level remaining is more than 10 percent. |
| • | The fuel alcohol content is less than 90 percent. |
| • | Intrusive tests are not in progress. |
| • | The scan tool output controls are not active. |
Rich Test Enable:
| • | The air fuel ratio is between 14.5:1-14.7:1. |
| • | For vehicles with throttle-actuated control (TAC), the throttle position (TP) indicated angle is between 3-70 percent more than the value observed at idle. |
| • | For vehicles without TAC, the TP is between 3-70 percent. |
Decel Fuel Cut-off Test Enable:
| • | Decel fuel cut-off (DFCO) is active. |
| • | The above condition is met for 3 second. |
Conditions for Setting the DTC
Rich Test
The HO2S voltage is more than 930 mV for 200 seconds.
Decel Fuel Cut-off Test
The HO2S voltage is more than 480 mV for 5 seconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | 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
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
Important: Never solder the HO2S wires. For proper wire and connector repair, refer to Wiring Repairs or Connector Repairs in Wiring Systems.
Inspect the following items:
| • | The fuel pressure--If the pressure is too high, the system will run rich. The PCM can compensate for some increase; however, if the pressure gets too high, this DTC may set. Refer to Fuel System Diagnosis . |
| • | A rich injector--Perform an Injector Balance test. Refer to Fuel Injector Balance Test with Tech 2 . |
| • | A leaking injector--Refer to Fuel System Diagnosis . |
| • | Fuel contaminated oil |
| • | Evaporative emission (EVAP) canister purge--Check for a fuel saturation. If full of fuel, check the canister control and hoses. Refer to Evaporative Emission Control System Description . |
| • | Leaking fuel pressure regulator diaphragm by checking the vacuum line to the regulator for fuel. |
| • | The TP sensor--An intermittent TP sensor output causes the system to run rich due to a false indication of the throttle moving. |
| • | False rich indication due to silicon contamination of the heated oxygen sensor--This DTC, accompanied by a lean driveability condition and a powdery white deposit on the sensor, may indicate a false rich condition. |
An intermittent may be caused by any of the following conditions:
| • | A poor connection |
| • | Rubbed through wire insulation |
| • | A broken wire inside the insulation |
Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
If a repair is necessary, then refer to Wiring Repairs or Connector Repairs in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
Monitor the HO2S voltage of the opposite bank sensor. If the voltage activity of the opposite bank sensor is similar to the voltage activity of the suspect sensor, inspect for rich conditions that would affect both cylinder banks. An opposite bank sensor with normal HO2S voltage activity indicates the suspect HO2S is defective or a rich condition exists only on the suspect HO2S cylinder bank.
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An HO2S contaminated by silicon will have a white, powdery deposit on the portion of the HO2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of unapproved silicon RTV engine gasket material or the use of silicon based sprays or fluids within the engine. If the cause of this contamination is not corrected, the replacement HO2S will also get contaminated.
Step | Action | Values | Yes | No | ||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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Important: This diagnostic applies only to vehicles built with isolated grounded HO2S. To identify the HO2S, refer to Engine Controls Component Views . Schematic Reference: Engine Controls Schematics | ||||||||||||||||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||||||||||||||
2 |
Is the HO2S voltage fixed more than the value specified? | 930 mV | Go to Step 5 | Go to Step 3 | ||||||||||||||||||||||
3 |
Is the HO2S voltage within the specified range? | 350-550 mV | Go to DTC P0140 or P0160 | Go to Step 4 | ||||||||||||||||||||||
4 |
Did you find and correct the condition? | -- | Go to Step 11 | Go to Diagnostic Aids | ||||||||||||||||||||||
5 |
Is the HO2S voltage within the value range specified? | 351-551 mV | Go to Step 6 | Go to Step 7 | ||||||||||||||||||||||
Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 9 | |||||||||||||||||||||||
7 |
Is the voltage more than the specified value? | 20 mV | Go to Step 8 | Go to Step 10 | ||||||||||||||||||||||
8 |
Important: The sensor may be damaged if the circuit is shorted to a voltage source. Repair the short to voltage in the HO2S high signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 11 | -- | ||||||||||||||||||||||
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Important: Before replacing a contaminated HO2S, determine and repair the cause of the contamination. Replace the HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 , or refer to Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 . Did you complete the replacement? | -- | Go to Step 11 | -- | |||||||||||||||||||||||
10 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- | ||||||||||||||||||||||
11 |
Does the DTC run and pass? | -- | Go to Step 12 | Go to Step 3 | ||||||||||||||||||||||
12 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||||||||||||||||
