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 P0137: HO2S Circuit Low Voltage Bank 1 Sensor 2
DTC P0138: HO2S Circuit High Voltage Bank 1 Sensor 2
DTC P0140: HO2S Circuit Insufficient Activity Bank 1 Sensor 2
DTC P0157: HO2S Circuit Low Voltage Bank 2 Sensor 2
DTC P0158: HO2S Circuit High Voltage Bank 2 Sensor 2
DTC P0160: HO2S Circuit Insufficient Activity Bank 2 Sensor 2

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
HO2S Bank 1 Sensor 1 Signal | P0131 | P0130 | P0132 | P0130, P0133, P0134
HO2S Bank 1 Sensor 2 Signal | P0137 | -- | P0138 | P0139, P0140
HO2S Bank 2 Sensor 1 Signal | P0151 | P0150 | P0152 | P0150, P0153, P0154
HO2S Bank 2 Sensor 2 Signal | P0157 | -- | P0158 | P0159, P0160
Low Reference | -- | P0130, P0150 | P0132, P0138, P0152, P0158 | --

### Typical Scan Tool Data

#### HO2S 1 or 2

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: Engine operating in Closed Loop. Parameter Normal Range: Fluctuates above and below 350-500 mV.
Sensor Signal | 0-60 mV | 400-415 mV | 5000 mV
Low Reference | -- | 400-415 mV | 5000 mV

### Circuit Description

The heated oxygen sensors (HO2S) are used for fuel control and catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the engine is started, the control module operates in an Open Loop mode, ignoring the HO2S signal voltage while calculating the air-to-fuel ratio. The control module supplies the HO2S with a reference, or bias voltage of about 450 mV. While the engine runs, the HO2S heats up and begins to generate a voltage within a range of 0-1,000 mV. This voltage will fluctuate above and below the bias voltage. Once sufficient HO2S voltage fluctuation is observed by the control module, Closed Loop is entered. The control module uses the HO2S voltage to determine the air-to-fuel ratio. An HO2S voltage that increases above bias voltage toward 1,000 mV indicates a rich fuel mixture. An HO2S voltage that decreases below bias voltage toward 0 mV indicates a lean fuel mixture.

The heating elements inside each HO2S heat the sensor to bring the sensor up to operating conditions faster. This allows the system to enter Closed Loop earlier and the control module to calculate the air-to-fuel ratio sooner.

### Conditions for Running the DTC

#### P0137 or P0157

• | DTCs P0117, P0118, P0125, and P0128 are not set.

• | The HO2S heater is at operating temperature.

• | The engine is operating for less than 1 second.

• | The ignition 1 voltage is more than 10.5 volts.

• | The engine coolant temperature is less than 40°C (104°F) at start-up and the engine coolant temperature was more than 60°C (140°F) when the ignition was turned OFF last ignition cycle.

• | The calculated exhaust temperature is between 250-800°C (482-1,472°F) for more than 90 seconds.

• | DTCs P0137 and P0157 run continuously once the above conditions are met.

#### P0138, P0140, P0158, or P0160

• | The engine is operating.

• | The ignition 1 voltage is more than 10.5 volts.

• | The HO2S heater is at operating temperature for more than 10 seconds.

• | The calculated exhaust temperature is between 250-800°C (482-1,472°F).

• | The DTCs run continuously once the above conditions are met for more than 90 seconds.

### Conditions for Setting the DTC

#### P0137 or P0157

• | The ECM detects that the HO2S signal voltage is less than 60 mV.

• | The condition exists for 4 seconds.

#### P0138 or P0158

• | The ECM detects that the HO2S signal voltage is more than 1,050 mV.

• | The condition exists for more than 4 seconds.

#### P0140 or P0160

• | The ECM detects that the HO2S voltage is between 400-500 mV for more than 60 seconds.

| OR

• | The ECM detects that the measured internal resistance of the HO2S is more than 40,000 ohms, when the calculated exhaust temperature is more than 600°C (1,112°F).

### Action Taken when the DTC Sets

DTCs P0137, P0138, P0140, P0157, P0158, and P0160 are Type B DTCs.

### Conditions for Clearing the MIL/DTC

DTCs P0137, P0138, P0140, P0157, P0158, and P0160 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

1. With the engine running, observe the appropriate scan tool HO2S voltage parameter. The reading should fluctuate above and below the range of 350-550 mV.
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 Data List.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the applicable HO2S.
2. Ignition ON, test for 350-550 mV between the signal circuit and the low reference circuit.

⇒ | If less than the specified range, test the signal circuit and the low reference circuit for a short to ground or an open/high resistance. If the circuits test normal, replace the ECM.

⇒ | If greater than the specified range, test the signal circuit and the low reference circuit for a short to voltage. If the circuits test normal, replace the ECM.

3. Verify that the following conditions do not exist:

• | Lean fuel injectors--Refer to Fuel Injector Balance Test with Special Tool or Fuel Injector Balance Test with Tech 2

• | Low fuel system pressure--Refer to Fuel System Diagnosis

• | Fuel that is contaminated--Refer to Alcohol/Contaminants-in-Fuel Diagnosis

• | Exhaust leaks near the HO2S

• | Engine vacuum leaks

⇒ | If you find any of the above conditions, repair as necessary.

4. If all circuits test normal, replace the HO2S sensor.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 1

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 2

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