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 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 | P0134, P0135 | P0132 | P0133, P2096, P2097
HO2S Bank 1 Sensor 2 Signal | P0137 | P0140 | P0138 | P0140
HO2S Bank 2 Sensor 1 Signal | P0151 | P0154, P0155 | P0152 | P0153, P2098, P2099
HO2S Bank 2 Sensor 2 Signal | P0157 | P0160 | P0158 | P0160
Low Reference | -- | P0134, P0135, P0154, P0155 | -- | --

### Typical Scan Tool Data

#### Bank 1 or 2 HO2S 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 | 400-455 mV | 1275 mV
Low Reference | -- | 400-455 mV | 1275 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 DTCs

#### P0137 and P0157 Condition 1

• | DTC P0036, P0037, P0038, P0056, P0057, P0058, P0116, P0117, P0118, P0119, or P0128 is not set.

• | The ignition voltage is greater than 10 volts within 5 seconds of engine start.

• | The engine speed is greater than 25 RPM.

• | The HO2S 2 heater is at operating temperature and the heater command is stable for greater than 30 seconds.

• | The engine coolant temperature (ECT) during the previous ignition cycle was warmer than 60°C (140°F).

• | The engine coolant temperature is colder than 40°C (104°F).

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

#### P0137 and P0157 Condition 2

• | DTC P0036, P0037, P0038, P0056, P0057, P0058, P0116, P0117, P0118, P0119, or P0128 is not set.

• | The ignition voltage is greater than 10 volts for greater than 40 seconds.

• | The engine speed is greater than 25 RPM.

• | The HO2S 2 heater is at operating temperature and the heater command is stable for greater than 30 seconds.

• | The Closed Loop fuel control is commanding the air/fuel ratio rich, greater than 5 percent.

• | DTCs P0137 and P0157 run continuously when the above conditions are met for greater than 600 seconds.

#### P0138, P0140, P0158 and P0160

• | The ignition voltage is greater than 10 volts.

• | The engine speed is greater than 25 RPM.

• | The HO2S 2 heater is at operating temperature and the heater command is stable for greater than 30 seconds.

• | DTCs P0138 and P0158 run continuously when the above conditions are met for greater than 5 seconds.

• | DTCs P0140 and P0160 run continuously when the above conditions are met for greater than 60 seconds.

### Conditions for Setting the DTC

#### P0137 or P0157 Condition 1

The ECM detects that the HO2S 2 signal voltage is less than 60 mV for greater than 1 second or for a cumulative of 10 seconds

#### P0137 or P0157 Condition 2

The ECM detects that the HO2S 2 signal voltage is less than 60 mV and the Closed Loop fuel control is commanding the air/fuel ratio rich, for greater than 1 second or for a cumulative of 10 seconds.

#### P0138 or P0158

The ECM detects that the HO2S signal voltage is greater than 1,150 mV for greater than 1 second or for a cumulative of 10 seconds.

#### P0140 or P0160

• | The ECM detects that the HO2S voltage is between 401-519 mV, when the calculated exhaust temperature is colder than 800°C (1472°F).

• | The ECM detects that the HO2S voltage is between 401-548 mV, when the calculated exhaust temperature is 800°C (1472°F) or warmer.

• | The ECM detects that the measured internal resistance of the HO2S is greater than 40,000 ohms, when the calculated exhaust temperature is warmer than 450°C (802°F).

• | The ECM detects any of the above conditions for greater than 1 second or for a cumulative of 10 seconds.

### 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

Component 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

Control Module References for scan tool information

### Circuit/System Verification

1. Engine idling, observe the appropriate scan tool heated oxygen sensor (HO2S) voltage parameter. The reading should fluctuate above and below the range of 401-548 mV.
2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the appropriate HO2S.
2. Ignition ON, verify the scan tool HO2S voltage parameter is between 400-520 mV.

⇒ | If less than the specified value, test the signal circuit terminal B for a short to ground. If the circuit/connections test normal, replace the ECM.

⇒ | If greater than the specified value, test the signal circuit terminal B for a short to voltage. If the circuit/connections test normal, replace the ECM.

3. Connect a 3A fused jumper wire between the signal circuit terminal B and ground. Verify the scan tool HO2S voltage parameter is less than 60 mV.

⇒ | If greater than the specified value, test the signal circuit for an open/high resistance. If the circuit/connections test normal, replace the ECM.

4. Connect a 3A fused jumper wire between the signal circuit terminal B and the low reference circuit terminal A. Verify the scan tool HO2S voltage parameter is less than 60 mV.

⇒ | If greater than the specified value, test the low reference circuit for an open/high resistance or for a short to voltage. If the circuit/connections test normal, replace the ECM.

5. Verify that the following conditions do not exist:

• | Lean, rich, or leaking fuel injectors--Refer to Fuel Injector Solenoid Coil Test.

• | A fuel pressure that is too low or too high--Refer to Fuel System Diagnosis.

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

• | Evidence of water intrusion into the electrical connector of the HO2S

• | The HO2S is loose

• | Exhaust leaks near the HO2S

• | Engine vacuum leaks

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

6. If all circuits/connections test normal, replace the appropriate HO2S.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 2

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 2

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