Diagnostic Instructions

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

P0137 and P0157 Condition 2

P0138, P0140, P0158 and P0160

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

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

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.