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	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

P0138, P0140, P0158, or P0160

Conditions for Setting the DTC

P0137 or P0157

P0138 or P0158

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. With the engine idling, observe the appropriate scan tool HO2S voltage parameter. The reading should fluctuate above and below the range of 350-550 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 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 terminal 4 and the low reference circuit terminal 3.

⇒	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.