DTC P0137 or P0157. Chevrolet Express 2002

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2002 🢒 Express 🢒 Engine 🢒 Engine Controls - 4.3L 🢒 DTC P0137 or P0157

Circuit Description

The heated oxygen sensor (HO2S) is a sensor designed to create a voltage relative to the oxygen content in the engine exhaust stream. The control module supplies the HO2S with signal high and low circuits. Ignition voltage and ground are supplied to the HO2S heater by independent circuits. The oxygen content of the exhaust indicates when the engine is operating lean or rich. When the HO2S detects that the engine is operating rich, the signal voltage is high. When the HO2S detects that the engine is operating lean, the signal voltage is low. This oscillation above and below the bias voltage, sometimes referred to as activity or switching, can be monitored with the HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm the sensor to the operating temperature. The heater also maintains the operating temperature during extended idle conditions. The HO2S needs to be at a high temperature in order to produce a voltage. When the HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors the HO2S signal voltage for Closed Loop fuel control. During normal Closed Loop fuel control operation, the control module will add fuel, or enrich the mixture, when the HO2S detects a lean exhaust content. The control module will subtract fuel, or "lean out" the mixture, when the HO2S detects a rich exhaust condition.

This DTC is designed to detect an HO2S voltage that remains low for more than a specified number of seconds during the test conditions.

Conditions for Running the DTC

•	DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0401, P0404, P0405, P0440, P0442, P0446, P0452, P0453, P1404, or P1441 are not set.

•	The ignition 1 signal is between 9-18 volts.

•	The fuel tank level remaining is more than 10 percent.

•	The loop status is closed.

•	Intrusive tests are not in progress.

•	Scan tool output controls are not active.

Lean Test Enable

•	The air fuel ratio is between 14.5:1 and 14.7:1.

•	The throttle position (TP) is between 3-70 percent.

Power Enrichment Test Enable

•	Power Enrichment is active

•	The above condition is met for 2 seconds.

Conditions for Setting the DTC

Lean Test

The HO2S voltage is less than 26 mV for 390 seconds.

Power Enrichment Test

The HO2S voltage is less than 400 mV for 10 seconds.

Action Taken When the DTC Sets

•	The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.

•

The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

•	The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

•	A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

•	A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

•	Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

•	Inspect the HO2S--The sensor pigtail may be in contact with the exhaust manifold or with the exhaust system.

•	Check the HO2S oxygen supply--An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provide the supply of oxygen. Inspect the HO2S wires and connections for breaks or contamination. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

•	Check for an intermittent ground in the signal wire between the connector and the sensor--Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

•	Inspect the lean fuel injectors--Perform the Fuel Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2 , or refer to Fuel Injector Balance Test with Special Tool .

•	Check for fuel contamination--Water near the in-tank fuel pump inlet can be delivered to the injectors. The water causes a lean exhaust and can set a DTC. Refer to Fuel Injector Balance Test with Tech 2 .

•	Check the fuel pressure--The system will be lean if the fuel pressure is low. Refer to Fuel System Diagnosis .

•	Check for exhaust leaks--An exhaust leak near the HO2S can cause a lean condition. Refer to Exhaust Leakage in Engine Exhaust.

•	Check for vacuum leaks or for crankcase leaks that can cause a lean condition.

•	If the components listed above are OK, the HO2S may be at fault.

For an intermittent condition, refer to Symptoms - Engine Controls .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

If the voltage is below the specified value the condition is present.

Jumpering the HO2S low signal circuit to ground is necessary for the PCM to correctly measure the voltage on the HO2S high signal circuit. If the HO2S voltage is within the specified range, the PCM and HO2S high signal circuit are OK.

Step

Action

Value(s)

Yes

Schematic Reference: Engine Controls Schematics

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

Important: With the engine running, observe the front HO2S voltage using a scan tool. If the front HO2S voltage is fixed above 900 mV, refer to DTC P0132 or P0152 .

Allow the engine to reach operating temperature.
With a scan tool, observe the HO2S voltage for the sensor that applies to this DTC.

Is the HO2S voltage less than the specified value?

26 mV

Go to Step 5

Go to Step 3

Change the throttle position more than 5 percent within 1 second, 6 times.
Observe the affected HO2S voltage with a scan tool.

Is the HO2S voltage within the specified range?

350-550 mV

Go to DTC P0140 or P0160

Go to Step 4

Observe the Freeze Frame/Failure Records data for this DTC.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame/Failure Records data that you observed.

Does the DTC fail this ignition?

Go to Step 5

Go to Diagnostic Aids

Turn OFF the ignition.
Disconnect the HO2S connector for the sensor that applies to this DTC.
Jumper the HO2S low signal circuit terminal on the engine harness side to a known good ground.
Turn ON the ignition, with the engine OFF.
Observe the HO2S voltage with a scan tool.

Is the HO2S voltage within the specified range?

350-550 mV

Go to Step 6

Go to Step 7

The HO2S may be detecting a lean exhaust condition. Check for the following conditions:

•	Water intrusion into the HO2S connector

•	Exhaust leak between the HO2S and the engine

•	Vacuum leaks

•	Incorrect fuel pressure

•	Lean fuel injectors

•	An inaccurate mass airflow (MAF) sensor

Repair any of the above or similar engine conditions as necessary.