For 1990-2009 cars

### Circuit Description

The DTC P0135 Heated Oxygen Sensor (HO2S) Heater Performance Bank 1 Sensor 1 diagnostic monitors the operation of the heater of the bank 1 HO2S 1. The DTC P0155 Heated Oxygen Sensor (HO2S) Heater Performance Bank 2 Sensor 1 diagnostic monitors the operation of the heater of the bank 2 HO2S 1. The heated oxygen sensors (HO2S) 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 to become active. The oxygen sensor heater is required by the post-catalyst HO2S 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 current of the HO2S heater is more than 5.3 amps or less than 0.15 amps when the heater is ON.

• | The voltage of the HO2S heater is more than 13.8 volts or less than 8.7 volts when the heater is ON.

• | The voltage of the HO2S heater is 6 volts with the heater OFF.

• | One of the above conditions is present for 3 seconds.

### Action Taken When the DTC Sets

• | The powertrain control module (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.

### Conditions for Clearing the MIL/DTC

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

• | A history DTC will clear after 40 consecutive warm-up cycles without a fault.

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

### Diagnostic Aids

1. Check the resistance of the HO2S relay. The resistance across terminal 3 and terminal 4 is 79-95 ohms at 20°C (68°F). The resistance across terminal 1 and terminal 2 is infinite.
2. The HO2S relay electrical contacts may be pitted or sticking. Replace the HO2S relay if tapping gently on the relay or wiggling the relay causes a change in the relay's operation.
3. The performance of the HO2S relay may be affected by temperature. Check the HO2S relay after sitting outside overnight and after running the engine 30 minutes.
4. If a DTC P0135 or a DTC P0155 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 .

An intermittent malfunction may be caused by a problem in the HO2S 2 sensor electrical circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .

If the DTC P0135 or DTC P0155 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.

Use the following relay cavity table in order to locate the correct cavities to probe during diagnosis. The table layout corresponds to the cavity layout of the relay connector.

Relay Cavity Identification
Switch Power
Switch Load
Coil Power | Coil Ground

### 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 measures the resistance of the heater circuit of the HO2S.

3. The PCM turns ON the HO2S heater when the engine is running. A test lamp that is ON steady or flashing, indicates that the HO2S heater control circuit is OK.

4. This step checks for a short to ground in the HO2S heater circuit. If no problem is found in the HO2S heater circuit, the problem may be a faulty or shorted HO2S.

5. Clearing the DTCs by removing the DOME fuse also clears the PCM long term memory. Using the scan tool to clear DTCs leaves the long term memory active. DTC emitting diagnostics may not run to completion as expected unless the long term memory is cleared. Removal of the DOME fuse also clears the time display of the radio. The DTC P0135 or DTC P0155 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0135 or DTC P0155 appears in the Not Ran Since Code Cleared list, the DTC P0135 or DTC P0155 diagnostic has not yet run. When the DTC P0135 or DTC P0155 does not appear in the Not Ran Since Code Cleared list, the DTC P0135 or DTC P0155 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the DTC P0135 or DTC P0155 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status, in order to determine the outcome of the diagnostic test involved.

Step | Action | Value(s) | 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 | Use a scan toolin order to check for the following HO2S Heater Circuit Performance DTCs:

• | DTC P0135

• | DTC P0141

• | DTC P0155

• | DTC P0161

Are there two or more DTCs set from the list above?

--

Go to Step 7

Go to Step 3

3 |

1. Turn OFF the ignition.
2. Disconnect the electrical connector of the HO2S.
3. Turn ON the ignition, leaving the engine OFF.
4. Probe the harness side of the ignition feed circuit of the HO2S connector using a test lamp connected to ground.

Does the test lamp illuminate?

--

Go to Step 4

Go to Step 7

4 |

1. Turn OFF the ignition.
2. Disconnect the HO2S electrical connector.
3. Measure the resistance between the HO2S terminal 3 and terminal 4 at the HO2S pigtail on the sensor side using the DMM.

Is the HO2S heater resistance within the specified range?

3.0-3.6 ohms at 20°C (68°F)

Go to Step 5

Go to Step 19

5 |

1. Connect a test lamp from B+ to the PCM side of the HO2S heater control circuit.
2. Start the engine.

Did the test lamp illuminate only when the engine was running?

--

Go to Diagnostic Aids

Go to Step 6

6 |

1. Turn OFF the ignition.
2. Connect the HO2S electrical connector.
3. Disconnect the PCM electrical connectors.
4. Turn ON the ignition, leaving the engine off.
5. Measure the voltage of the HO2S heater control circuit at the PCM connector, using a DMM.

Is the voltage more than the specified value?

10 V

Go to Step 20

Go to Step 16

7 | Inspect the HO2S fuse. Is the HO2S fuse open? | -- | Go to Step 14 | Go to Step 8
8 |

1. Turn OFF the ignition.
2. Disconnect the HO2S relay from the wiring harness.
3. Turn ON the ignition, leaving the engine off.
4. Probe terminal 1 of the relay electrical connector using a test lamp connected to ground. Refer to the Relay Cavity Identification table in Diagnostic Aids.

Does the test lamp illuminate?

--

Go to Step 9

Go to Step 11

9 | Probe terminal 3 of the HO2S relay electrical connector using a test lamp connected to ground. Does the test lamp illuminate? | -- | Go to Step 10 | Go to Step 13
10 |

1. Turn OFF the ignition.
2. Probe terminal 4 of the HO2S relay using a test lamp connected to B+.
3. Observe the test lamp.

Does the test lamp illuminate?

--

Go to Step 17

Go to Step 12

11 | Repair the open in the ignition positive voltage circuit between the IG fuse and the HO2S relay. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 22 | --
12 |

1. Check for an open or a poor connection in the in the HO2S relay ground circuit between the HO2S relay and G104.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 22

--

13 | Repair the open in the ignition positive voltage circuit between the IG fuse and the HO2S relay. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 22 | --
14 |

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

Was a repair necessary?

--

Go to Step 22

Go to Step 15

15 | Replace the faulty HO2S that has an internally shorted the heater element. Refer to Heated Oxygen Sensor 1 Replacement . Did you complete the replacement? | -- | Go to Step 22 | --
16 | Repair the open circuit or the short to ground in the HO2S heater control circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 22 | --
17 |

1. Inspect the HO2S relay circuit for an open or a poor connection, from terminal 2 to the HO2S.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct a wiring problem?

--

Go to Step 22

Go to Step 18

18 | Replace the HO2S relay. Did you complete the replacement? | -- | Go to Step 22 | --
19 | Replace the HO2S. Refer to Heated Oxygen Sensor 1 Replacement . Did you complete the replacement? | -- | Go to Step 22 | --
20 |

1. Check for a faulty connection at the HO2S electrical connector. 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 22

Go to Step 21

21 | Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 22 | --
22 |

1. Turn OFF the ignition.
2. Remove the DOME fuse for 30 seconds.
3. Install the DOME fuse.
4. Reset the radio clock time. Refer to Radio/Audio System Description and Operation in Entertainment.
5. Start the engine.
6. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or until the DTC P0135 or DTC P0155 diagnostic test has run.

Does the DTC run and pass?

--

Go to Step 23

Go to Step 2

23 | 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