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 Sensor 2

DTC P0138

HO2S Circuit High Voltage Sensor 2

DTC P0140

HO2S Circuit Insufficient Activity Sensor 2

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
HO2S Sensor 1 Signal	P0131	P0134, P0135	P0132	P0133, P2096, P2097
HO2S Sensor 2 Signal	P0137	P0140	P0138	P0140
Low Reference	-	P0134, P0135	-	-

Typical Scan Tool Data

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 0-1000 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 1000 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

•	DTC P0117 or P0118 is not set.

•	The HO2S 2 is at operating temperature for greater than 90 seconds.

•	The engine is operating for greater than 5 seconds.

•	The ignition voltage is greater than 10 volts.

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

•	DTCs P0137 runs continuously once the above conditions are met.

P0138 and P0140

•	The HO2S 2 is at operating temperature for greater than 30 seconds.

•	The engine is operating for greater than 1 second.

•	The ignition voltage is greater than 10 volts.

•	DTCs P0138 runs continuously once the above conditions are met for greater than 5 seconds.

•	DTCs P0140 runs continuously once the above conditions are met for greater than 60 seconds.

Conditions for Setting the DTC

P0137

The ECM detects that a secondary HO2S signal voltage is less than 60 mV for greater than 1 seconds of for a cumulative of 10 seconds.

P0138

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

P0140

•	The ECM detects that the HO2S 2 signal voltage is between 401-519 mV, when the calculated exhaust temperature is less than 800°C (1,472°F).

•	The ECM detects that the HO2S 2 signal voltage is between 401-548 mV, when the calculated exhaust temperature is greater than 800°C (1,472°F).

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

•	The ECM detects any one 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, and P0140 are Type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0137, P0138, and P0140 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 scan tool HO2S 2 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 you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

1.	Ignition OFF, disconnect the harness connector at the B52 HO2S 2.

2.	Ignition ON, verify that the scan tool HO2S 2 voltage parameter is between 350-500 mV.

3.	If less than the specified range, test the signal circuit terminal 4 for a short to ground. If the circuit/connections test normal, replace the K20 ECM.

4.	If greater than the specified range, test the signal circuit terminal 4 for a short to voltage. If the circuit/connections test normal, replace the K20 ECM.

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

6.	If greater than the specified range, test the signal circuit for an open/high resistance. If the circuit/connections test normal, replace the K20 ECM.

7.	Connect a 3 A fused jumper wire between the signal circuit terminal 4 and the low reference circuit terminal 3. Verify the scan tool HO2S 2 voltage parameter is less than 60 mV.

8.	If greater than the specified range, test the low reference circuit for an open/high resistance, or for a short to voltage. If the circuit/connections test normal, replace the K20 ECM.

9.	Verify 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.

10.	If all circuits/connections test normal, replace the B52 HO2S 2 sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

•	Heated Oxygen Sensor Replacement - Sensor 2

•	Control Module References for Engine Control Module replacement, setup, and programming