Diagnostic Instructions

DTC Descriptor

DTC P0131 00: HO2S Circuit Low Voltage Sensor 1

DTC P0132 00: HO2S Circuit High Voltage Sensor 1

DTC P0137 00: HO2S Circuit Low Voltage Sensor 2

DTC P0138 00: HO2S Circuit High Voltage Sensor 2

Diagnostic Fault Information

HO2S 1 Circuit	Short to Ground	Open	Short to Voltage	Signal Performance
HO2S Signal	P0131 00, P0171 00	P0132 00, P0134 00, P0137 00, P2A00 00	P0132 00, P0134 00	P0133 00, P1133 00, P2A00 00
Low Reference	--	P0134 00, P0137 00	--	P0133 00, P1133 00, P2A00 00

HO2S 2 Circuit	Short to Ground	Open	Short to Voltage	Signal Performance
HO2S Signal	P0137 00	P0138 00, P0140 00	P0132 00, P0134 00	--
Low Reference	--	P0138 00, P0140 00	--	--

Typical Scan Tool Data

HO2S 1 and 2 Circuit	Short to Ground	Open	Short to Voltage	Signal Performance
Operating Conditions: Engine operating in closed loop Parameter Normal Range: 50-1050 mV
HO2S 1 and 2 Signal	0 mV	1275 mV	1275 mV	--
Low Reference	--	1275 mV	--	--

Circuit/System Description

Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each heated oxygen sensor (HO2S) compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. Each heated oxygen sensor (HO2S) must reach operating temperature to provide an accurate voltage signal. Heating elements inside both of the heated oxygen sensors (HO2S) minimize the time required for the sensors to reach operating temperature. The engine control module (ECM) supplies both heated oxygen sensor (HO2S) with a reference, or bias, voltage of about 450 mV. When the engine is first started, the ECM operates in open loop, ignoring the heated oxygen sensor (HO2S) voltage signals. Once both the heated oxygen sensor (HO2S) reaches operating temperature and closed loop is achieved, both heated oxygen sensor (HO2S) generates a voltage within a range of 0-1000 mV that fluctuates above and below bias voltage. High heated oxygen sensor (HO2S) voltage indicates a rich exhaust stream. Low heated oxygen sensor (HO2S) voltage indicates a lean exhaust stream.

The heating elements inside each heated oxygen sensor (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

Conditions for Setting the DTC

P0131 00 or P0137 00

The engine control module (ECM) detects that the heated Oxygen Sensor (HO2S) voltage is less than 50 mV for greater than 38 s for DTC P0131 00 or 43 s for DTC P0137 00.

P0132 00 or P0138 00

The ECM detects that the heated Oxygen Sensor (HO2S) voltage is greater than 1050 mV for greater than 10 s.

Action Taken When the DTC Sets

DTCs P0131 00, P0132 00, P0137 00, and P0138 00 are Type B DTCs.

Conditions for Clearing the DTC

DTCs P0131 00, P0132 00, P0137 00, and P0138 00 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. Clear the DTCs with a scan tool.
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 B52A Heated Oxygen Sensor (HO2S) or B52B Heated Oxygen Sensor (HO2S).
2. Ignition OFF, measure for less than 5 Ω between the B52A  Heated Oxygen Sensor (HO2S) or B52B Heated Oxygen Sensor (HO2S) low signal circuit terminal 3 and ground.

⇒	If more than the specified range, test the appropriate B52A Heated Oxygen Sensor (HO2S) or B52B Heated Oxygen Sensor (HO2S) low signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K20 Engine Control Module (ECM)

3. Ignition ON, test for 1.5-2.1 V between the B52A Heated Oxygen Sensor (HO2S) or B52B Heated Oxygen Sensor (HO2S) signal circuit terminal 4 and ground.

⇒	If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K20 Engine Control Module (ECM)

⇒	If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the K20 Engine Control Module (ECM)

4. Install a 3 A fused jumper wire between the B52A Heated Oxygen Sensor (HO2S) or B52B Heated Oxygen Sensor (HO2S) signal circuit terminal 4 and the low reference circuit terminal 3. Engine running, verify the scan tool HO2S 1 or HO2S 2 parameter is less than 60 mV.

⇒	If greater than the specified value, replace the K20 Engine Control Module (ECM).

5. Verify none of the following conditions exist:

•	Lean or rich fuel injectors, refer to Fuel Injector Diagnosis.

•	Water intrusion in the HO2S harness connector

•	Low or high fuel system pressure, refer to Fuel System Diagnosis.

•	Fuel that is contaminated, refer to Alcohol/Contaminants-in-Fuel Diagnosis.

•	Fuel saturation of the evaporative emission (EVAP) canister

•	Exhaust leaks near the HO2S

•	Engine vacuum leaks

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

6. If all circuits test normal, test or replace the appropriate B52A Heated Oxygen Sensor (HO2S) or B52B Heated Oxygen Sensor (HO2S).

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.