For 1990-2009 cars

### Circuit Description

The DTC P0135 Heated Oxygen Sensor (HO2S) Heater Performance Sensor 1 diagnostic monitors the operation of the HO2S 1 heater circuit. The DTC P0141 HO2S heater performance sensor 2 diagnostic monitors the operation of the HO2S 2 heater circuit. The heaters in the oxygen sensors increase the amount of time the sensor spends in Closed Loop fuel control operation or catalyst monitoring operation. The oxygen sensor heater greatly reduces the amount of time required for the fuel control HO2S 1 to become active. The oxygen sensor heater is required by the post-catalyst HO2S 2 in order to maintain the high operating temperatures. The heater helps provide accurate oxygen content readings of the engine exhaust by the HO2S.

### Conditions for Running the DTC

The engine is running.

### Conditions for Setting the DTC

• | The HO2S heater current exceeds 2 amps.

• | The HO2S heater current is 0.2 amp or less.

### Action Taken When the DTC Sets

• | The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault active.

• | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.

• | The PCM will turn OFF the heater in the oxygen sensor.

### Conditions for Clearing the MIL/DTC

• | The MIL turns OFF after 3 consecutively passing trips without a fault present.

• | A History DTC clears after 40 consecutive warm-up cycles without a fault.

• | Use the scan tool Clear DTC Information function in order to clear the DTC.

### Diagnostic Aids

Check for any of the following conditions:

• | If a DTC P0135 or DTC P0141 is intermittent, driving the vehicle under the conditions outlined in the Inspection/Maintenance (I/M) section can verify whether the fault is present. Refer to Inspection/Maintenance Heated Oxygen Sensor Heater System Set .

• | The HO2S heater diagnostic checks for many of the faults that can cause DTC P0135 or P0141 to set. If the HO2S heater test passes, the cause of the DTC is probably intermittent. Clear the DTC information. Road test the vehicle while monitoring the HO2S heater test in the I/M System Information selection on the scan tool. When the HO2S heater test indicates complete with a YES status, check for a DTC P0135 or P0141 under Last Test Failed. If there is no DTC P0135 or P0141 indicated, the DTC is intermittent and the HO2S heater diagnostic is indicating OK at this time.

• | An intermittent malfunction may be caused by a fault in the HO2S 1 sensor electrical circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .

• | Repair any electrical circuit faults that were found. Refer to Wiring Repairs in Wiring Systems.

### Test Description

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

1. The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. This step checks whether the malfunction that caused the DTC P0135 or P0141 is still present. Operating the vehicle in check mode enhances the diagnostic capabilities of the PCM. The HO2S Heater diagnostic can be monitored on the scan tool under the I/M System Information selection of System Information. When the HO2S Heater test displays a YES status, indicating that the oxygen sensor heater diagnostic is completed, check for a DTC P0135 or P0141 in the Last Test Failed screen of the scan tool. If there is no DTC P0135 or P0141 displayed the HO2S heater diagnostic has run and passed, indicating that no malfunction was present this time. The DTCs MUST be cleared in order to view the Current Status of the system diagnostics being performed. Do not forget that I/M System Information tests only indicate that the test has run, not whether the test passed or failed. The Last Test Failed screen must be checked for related DTCs in order to determine the outcome of the diagnostic test involved. For additional information on check mode operation refer to Powertrain Control Module Diagnosis.

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Engine Controls Schematics
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 |

1. Perform the scan tool Clear DTC Information function.
2. Operate the vehicle within the Conditions for Running the DTC or until the HO2S heater test is complete. Review the supporting text.

Did a DTC P0135 or P0141 set?

Go to Step 3

Go to Diagnostic Aids

3 |

1. Turn ON the ignition, with the engine OFF.
2. Disconnect the electrical connector of the HO2S that failed the diagnostic.
3. Probe the ignition positive voltage circuit, on the engine harness side, using a test lamp connected to ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 8

4 |

1. Turn ON the ignition, with the engine OFF.
2. Probe the heater control circuit on the engine harness side, using a test lamp connected to B+.

Does the test lamp illuminate?

Go to Step 6

Go to Step 5

5 | Start and idle the engine. Does the test lamp illuminate? | Go to Step 9 | Go to Step 7
6 |

1. Check the HO2S heater control circuit for a short to ground.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

Go to Step 12

Go to Step 11

7 |

1. Check for an open in the HO2S heater control circuit.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

Go to Step 12

Go to Step 11

8 |

1. Check for an open in the ignition feed circuit.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 12

--

9 |

1. Check the electrical connections at the HO2S. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

Go to Step 12

Go to Step 10

10 | Replace the HO2S. Refer to Heated Oxygen Sensor 1 Replacement or Heated Oxygen Sensor 2 Replacement . Is the action complete? | Go to Step 12 | --
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | Go to Step 12 | --
12 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC or until the HO2S Heater test is complete. Review the supporting text.

Does the DTC run and pass

Go to Step 13

Go to Step 2

13 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | Go to Diagnostic Trouble Code (DTC) List | System OK