For 1990-2009 cars
Engine Controls Components
HO2S Sensors
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The PCM supplies a bias voltage of about 450 mV between the HO2S signal and low circuits. When measured with a 10 megohm digital voltmeter, this may display as low as 320 mV. The oxygen sensor varies the voltage within a range of about 1000 mV when the exhaust is rich, down through about 10 mV when exhaust is lean. The PCM constantly monitors the HO2S signal during closed loop operation and compensates for a rich or lean condition by decreasing or increasing injector pulse width as necessary. If the Bank 1 HO2S 1 voltage remains at or near the 450 mV bias for an extended period of time, DTC P0134 will be set, indicating an open sensor signal or sensor low circuit.

### Conditions for Running the DTC

• | No Misfire, CKP, Fuel Injector, MAF, TP, EVAP, IAT, MAP, Fuel Trim, EGR or ECT DTCs are present.

• | Engine has been running for longer than 4 minutes.

### Conditions for Setting the DTC

Bank 1 HO2S 1 signal voltage remains between 400 mV and 500 mV.

### Action Taken When the DTC Sets

• | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.

• | The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.

### Conditions for Clearing the MIL/DTC

• | The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed.

• | The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

• | The DTC can be cleared by using the scan tool.

### Diagnostic Aids

Check for the following conditions:

• | Poor connection at the PCM - Inspect harness connectors for the following conditions:

- | Backed out terminals.

- | Improper mating.

- | Broken locks.

- | Improperly formed or damaged terminals.

- | Poor terminal to wire connection.

• | Damaged harness -- Inspect the wiring harness for damage. If the harness appears to be OK, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the display will indicate the location of the fault.

• | Faulty HO2S heater or heater circuit -- With the ignition ON the HO2S voltage displayed on a scan tool should gradually drop to less than 250 mV or rise to greater than 600 mV. If not, disconnect the HO2S and connect a J 35616-200 Unpowered Test Light between the HO2S ignition feed and heater ground circuits. If the test light does not light, repair the open ignition feed or sensor ground circuit as necessary. Refer to Wiring Repairs . If the test light illuminates and the HO2S signal and low circuits are OK, replace the HO2S.

• | Intermittent test -- With the ignition ON, monitor the HO2S signal voltage while moving the wiring harness and related connectors. If the fault is induced, the HO2S signal voltage will change. This may help isolate the location of the malfunction.

Review the Freeze Frame/Fail Records vehicle mileage since the diagnostic test last failed. This may help determine how often the condition that caused the DTC to be set occurs.

### Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table:

1. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is replaced, the new PCM must be programmed.

#### DTC P0134 - HO2S Insufficient Activity Bank 1 Sensor 1

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Engine at operating temperature
2. Operate engine above 1200 RPM for two minutes.
3. With a scan tool, observe the HO2S voltage parameter.

Does scan tool indicate HO2S voltage varying outside the specified values?

400-500 mV

Go to Step 3

Go to Step 4

3 |

1. Turn ON the ignition, with the engine OFF.
2. With a scan tool, review and record Fail Records.
3. Operate vehicle within Fail Records conditions.

Does the scan tool indicate this DTC failed this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4 |

1. Turn ON the ignition.
2. Disconnect the HO2S and jumper the signal and low circuits (PCM side) to a good ground.
3. With a scan tool, observe HO2S voltage parameter.

Does the scan tool indicate HO2S voltage below the specified value?

150 mV

Go to Step 8

Go to Step 5

5 |

1. Remove the jumper wire from the HO2S signal circuit (leave the low circuit connected to ground).
2. Measure the voltage between the HO2S signal circuit (PCM side) and the HO2S heater ground circuit using a J 39200 Digital Multimeter.

Does HO2S signal voltage measure near the specified value?

4.5V

Go to Step 6

Go to Step 7

6 |

1. Turn OFF the ignition.
2. Disconnect the PCM.
3. Test for continuity of the HO2S low circuit.
4. If the HO2S low circuit measures over 5 ohms, repair open or poor connection as necessary. Refer to Wiring Repairs or Connector Repairs .

Did you find and correct the condition?

--

Go to Step 13

Go to Step 9

7 |

1. Turn OFF the ignition.
2. Disconnect the PCM.
3. Test for continuity of the HO2S signal circuit and the HO2S low circuit.
4. If either circuit measures over 5 ohms, repair open or poor connection as necessary. Refer to Wiring Repairs or Connector Repairs .

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

8 | Inspect for a poor HO2S signal or a HO2S low circuit connection at the HO2S. Refer to Connector Repairs . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 11
9 | Inspect for a poor HO2S signal or a HO2S low circuit connection at the PCM. Refer to Intermittents and Poor Connections Diagnosis and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12
10 | Inspect for a poor HO2S signal or a HO2S low circuit connection at the PCM. Refer to Intermittents and Poor Connections Diagnosis and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12
11 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement . Did you complete the replacement? | -- | Go to Step 13 | --
12 | Important: Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Did you complete the replacement? | -- | Go to Step 13 | --
13 |

1. Use the scan tool in order to clear DTCs.
2. Operate the vehicle within the Fail Record conditions.

Does the DTC reset?

--

Go to Step 2

System OK