For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provide an overview of each diagnostic category.

### DTC Descriptors

DTC P0135: HO2S Heater Performance Bank 1 Sensor 1
DTC P0141: HO2S Heater Performance Bank 1 Sensor 2
DTC P0155: HO2S Heater Performance Bank 2 Sensor 1
DTC P0161: HO2S Heater Performance Bank 2 Sensor 2

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Ignition 1 Voltage | P0135, P0141 | P0135, P0141 | -- | --
HO2S 1 Heater Control | P0135 | P0135 | P0135 | --
HO2S 2 Heater Control | P0141 | P0141 | P0141 | --

### Circuit Description

The heated oxygen sensor (HO2S) heater reduces the time required for the oxygen sensor to reach operating temperature and maintains the operating temperature during extended idle periods. When the ignition is turned to the ON position, ignition voltage is supplied directly to the sensor heater. The engine control module (ECM) controls the heater operation by first modulating the control circuit to ground when the sensors are cold. This prevents the possibility of thermal shock to the sensor, from condensation build-up on the sensor, by controlling the sensor's rate of heating. After a predetermined amount of time, the ECM commands the heaters ON continuously. Once the sensor reaches operating temperature, the ECM may modulate the heater control circuit to ground to maintain a desired temperature.

### Conditions for Running the DTC

#### P0135 or P0155

• | DTCs P0101, P0102, P0103, P0107, P0108, P0121, P0122, P0123, P0131, P0132, P0133, P0151, P0152, P0153, P0221, P0222, or P0223 are not set.

• | The engine is running.

• | The ignition 1 voltage is between 10-16 volts.

• | The exhaust gas temperature at the HO2S is less than 600°C (1,112°F).

• | The engine run time is greater than 4 minutes.

• | The DTCs run once a drive cycle. The ECM will attempt to run this diagnostic until results are obtained.

#### P0141 or P0161

• | DTCs P0101, P0102, P0103, P0121, P0122, P0123, P0221, P0222, or P0223 are not set.

• | The engine is running.

• | The ignition 1 voltage is between 10-16 volts.

• | The exhaust gas temperature at the HO2S is less than 600°C (1,112°F).

• | The engine run time is greater than 2 minutes.

• | The DTCs run once a drive cycle. The ECM will attempt to run this diagnostic until results are obtained.

### Conditions for Setting the DTC

#### P0135 or P0155

The ECM detects the heater resistance to be less than 1,200 ohms.

#### P0141 or P0161

The ECM detects the heater resistance to be less than 700 ohms.

### Action Taken When the DTC Sets

DTCs P0135, P0141, P0155, and P0161 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P0135, P0141, P0155, and P0161 are Type B DTCs.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Engine Control Module Connector End Views

• | Engine Controls Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

### Circuit/System Verification

Important: It may take up to 8 minutes for the DTC to set.

1. With the engine at normal operating temperature, operate the engine above 1,200 RPM for 30 seconds and then allow the engine to idle. DTCs P0135, P0141, P0155, or P0161 should not set.
2. If the vehicle passes the Circuit/System Verification Test, then operate the vehicle within the conditions for running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records List.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector of the appropriate HO2S.
2. Ignition ON, load test for battery voltage on the ignition voltage circuit of the HO2S heater.

⇒ | If less than B+, repair the ignition voltage circuit of the HO2S heater for a short to ground or an open/high resistance.

3. Ignition OFF, connect a test lamp between the control circuit of the HO2S heater and B+.

⇒ | If test lamp illuminates, test the control circuit of the HO2S heater for a short to ground. If the circuit tests normal, replace the ECM.

4. Ignition ON, test for less than 0.3 volt between the control circuit of the HO2S heater at the test lamp probe and ground.

⇒ | If greater than 0.3 volt, test the control circuit of the HO2S heater for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

5. If all circuits test normal, test or replace the HO2S.

### Component Testing

1. Ignition OFF, disconnect the harness connector of the appropriate HO2S.
2. Test the HO2S heater resistance for 3-35 ohms.

⇒ | If the resistance is out of the specified range, replace the HO2S.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 2

• | Control Module References for engine control module replacement, setup, and programming