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 provides an overview of each diagnostic category

### DTC Descriptors

DTC P0135: O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)
DTC P0141: O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)
DTC P0155: O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
DTC P0161: O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 2)

### Diagnostic Fault Information

Circuit | Short to Ground | High Resistance | Open | Short to Voltage | Signal Performance
--- | --- | --- | --- | --- | ---
HO2S Heater Voltage Supply | Opens fuse | P0030, P0036, P0050, P0053, P0054, P0056, P0059, P0060, P0135, P0141, P0155, P0161 | P0030, P0036, P0050, P0056, P0135, P0141, P0155, P0161 | -- | P0135, P0141, P0155, P0161
HO2S Heater Low Control | P0030, P0036 | P0030, P0036, P0050, P0053, P0054, P0056, P0059, P0060, P0135, P0141, P0155, P0161 | P0030, P0036, P0050, P0056, P0135, P0141, P0155, P0161 | P0030, P0036, P0050, P0056, P0135, P0141, P0155, P0161 | P0135, P0141, P0155, P0161

### Typical Scan Tool Data

#### HO2S Heater

Circuit | Normal Range | Short to Ground | Open | Short to Voltage
--- | --- | --- | --- | ---
HO2S Heater Low Control | 1-2 A | 0 A | 0 A | 0 A
HO2S Heater Voltage Supply | 1-2 A | 0 A | 0 A | 1-2 A

### Circuit/System Description

Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. A heating element inside the HO2S minimizes the time required for the sensor to reach operating temperature. Voltage is provided to the heater by an ignition voltage circuit through a fuse. With the engine running, ground is provided to the heater by the HO2S heater low control circuit, through a low side driver within the engine control module (ECM). The ECM commands the heater ON or OFF to maintain a specific HO2S operating temperature range.

If the ECM detects that the heater current is not within the expected range, DTC P0135 sets for HO2S bank 1 sensor 1, or DTC P0141 sets for HO2S bank 1 sensor 2, DTC P0155 sets for HO2S bank 2 sensor 1, or DTC P0161 sets for bank 2 sensor 2.

### Conditions for Running the DTC

#### DTC P0135 or P0155

• | DTCs P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0220, P0222, P0223, P0442, P0443, P0446, P0449, P0455, P0496, P1516, P2101, P2119, P2135, P2176 are not set.

• | The ECT Sensor parameter is more than 50°C (122°F).

• | The Ignition 1 Signal parameter is between 10-18 volts.

• | The mass air flow (MAF) sensor parameter is between 3-40 g/s.

• | The Engine Run Time parameter is more than 300 seconds.

• | The Engine Speed parameter is between 500-3,000 RPM.

• | DTC P0135 runs the heater current test once per drive cycle when the above conditions are met for 2 seconds.

#### DTC P0141 or P0161

• | DTCs P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0220, P0222, P0223, P0442, P0443, P0446, P0449, P0455, P0496, P1516, P2101, P2119, P2135, P2176 are not set.

• | The ECT sensor parameter is more than 50°C (122°F).

• | The Ignition 1 Signal parameter is between 10-18 volts.

• | The MAF sensor parameter is between 3-40 g/s.

• | The Engine Run Time parameter is more than 300 seconds.

• | The Engine Speed parameter is between 500-3,000 RPM.

• | DTC P0141 runs the heater current test twice per drive cycle when the above conditions are met for 2 seconds.

### Conditions for Setting the DTC

#### DTC P0135 or P0155

• | The ECM detects that the HO2S 1 heater current parameter is more than 3.125 amps or less than 0.25 amps.

• | DTC P0135 sets within 30 seconds during the heater current test when the above condition is met.

#### DTC P0141 or P0161

• | The ECM detects that the HO2S 2 heater current parameter is more than 1.375 amps or less than 0.25 amp.

• | DTC P0141 sets within 30 seconds during the heater current test when the above condition is met.

DTCs P0135, P0141, P0155 or P0161 are type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P0135, P0141, P0155 or P0161 are type B DTCs.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References

### Circuit/System Verification

• | Allow the engine to reach operating temperature. With the engine running, using a scan tool observe the HO2S Heater parameter l. The value should vary from below 2 A to above 1 A.

• | With the engine running at operating temperature, using a scan tool observe the HO2S Heater parameter manipulate the related wiring and connectors.

⇒ | If manipulation does affect the parameter then repair the harness or connector.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the appropriate HO2S.
2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal and a known ground.

⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test or replace the HO2S.

3. Ignition OFF, verify that the test lamp is OFF between the heater low control circuit terminal of the appropriate HO2S and B+.

⇒ | If the test lamp illuminates, test the low control circuit for a short to ground.

4. Connect a test lamp between the heater low control circuit terminal of the appropriate HO2S and the B+ circuit terminal.
5. With the engine running, the test lamp should be ON steady or flashing.

⇒ | If the test lamp is not ON steady or flashing, test the low control circuit for a short to voltage and for high resistance. If the circuit tests normal, replace the ECM .

6. Ignition OFF, install a 30-A fusible link wire between the B+ circuit terminal and the heater low control circuit of the appropriate HO2S.
7. With the engine running, use a scan tool to observe that the appropriate HO2S heater parameter indicates 0.0 amps.

⇒ | If the scan tool does not indicate 0.0 amps, test the heater B+ circuit and the low control circuit for resistance greater than 3 ohms. If the circuit tests normal, replace the ECM.

8. If all circuits test normal, test or replace the appropriate HO2S.

### Repair Instructions

Notice: Refer to Diagnostic System Check - Vehicle in the Preface section.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 1

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 2

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 1

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 2

• | Control Module References