DTC P0137 or P0157. Pontiac Firebird 2001

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 2001 🢒 Firebird 🢒 Engine 🢒 Engine Controls - 5.7L 🢒 DTC P0137 or P0157

Circuit Description

The powertrain control module (PCM) supplies a voltage of about 450 mV between the HO2S high and low signal circuits. The oxygen sensor varies the voltage from approximately 1,000 mV when the exhaust is rich, through approximately 10 mV when the exhaust is lean.

The PCM monitors and stores the heated oxygen sensor (HO2S) voltage information. The PCM evaluates the HO2S voltage samples in order to determine the amount of time the HO2S voltage was out of range. The PCM compares the stored HO2S voltage samples taken within each sample period and determines if majority of the samples are out of the operating range.

The PCM monitors the HO2S voltage for being fixed below a predetermined voltage. If the PCM detects the voltage is below a predetermined voltage, a DTC sets.

Conditions for Running the DTC

•	DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P121, P0122, P0123, P0200, P0300, P0410, P0440, P0442, P0446, P0452, P0453, P1258, P1415, P1416, or P1441 are not set.

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

•	The loop status is Closed.

•	The secondary air injection (AIR) and the catalyst diagnostics are not active.

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

•	The Fuel Trim Learn is enabled.

•	The air fuel ratio is between 14.5-14.7 percent.

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

Conditions for Setting the DTC

•	The HO2S signal voltage remains below 80 mV.

•	The conditions are present for 396 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.

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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 you diagnose or replace the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent contaminant intrusion into the PCM.

•	For any test that requires probing the PCM or probing the component harness connectors, use the J 35616 connector test adapter kit. Using this kit prevents any damage to the harness connector terminals. Refer to Using Connector Test Adapters in Wiring Systems.

The PCM sets this DTC when the vehicle runs out of fuel. Inspect the following components:

•	The heated oxygen sensor (HO2S) wire--The sensor pigtail may be in contact with the exhaust manifold or with the exhaust system.

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

•	An intermittent ground--Inspect for an intermittent ground in the signal wire between the connector and the sensor.

•	Lean injectors--Perform the Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2 or Fuel Injector Balance Test with Special Tool .

•	Fuel contamination--Water near the in-tank fuel pump inlet can be delivered to the injectors. Refer to Temperature Versus Resistance . The water causes a lean exhaust and can set a DTC.

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

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

Vacuum or crankcase leaks can cause a lean condition.

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

For an intermittent condition, refer to Intermittent Conditions .

Test Description

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

If the HO2S voltage is fixed well below 200 mV, this indicates a short to battery ground or chassis ground. If the voltage is fixed near or above 200 mV, this indicates a short to a PCM ground. When the HO2S voltage is fixed near 200 mV, indicates the DTC set when the fuel system was in a Power Enrichment mode of operation. This DTC sets if the HO2S voltage is less than 420 mV during a Power Enrichment mode of operation.

The engine must be at the normal operating temperature before you perform this test.

Using the Freeze Frame/Failure Records data may help to locate an intermittent condition. If you cannot duplicate the DTC, the information in the Freeze Frame/Failure Records can help to determine how many miles have occurred since the DTC set. The Fail Counter and the Pass Counter can also be used to determine the number of ignition cycles in which the diagnostic reported a pass and/or a fail. In order to isolate when the DTC failed, operate the vehicle within the same freeze frame conditions that the PCM recorded. These conditions include the RPM, the vehicle load, the vehicle speed, and the temperature.

Lower the exhaust system in order to gain sufficient access to the HO2S and/or to the HO2S connector, if necessary. Disconnecting the HO2S should cause the HO2S voltage to display a bias voltage. A voltage that stays near 0 volts indicates that the HO2S low signal circuit is open, or that the HO2S high signal circuit is open or grounded.

Disconnecting the PCM allows you to use a DMM in order in order to test the circuit continuity. This procedure helps to locate an open circuit or a shorted circuit.

Step

Action

Values

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

Start and run the engine until normal operating temperature is reached.
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?

80 mV

Go to Step 4

Go to Step 3

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 4

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.
Use a scan tool in order to observe the HO2S voltage.

Is the HO2S voltage within the specified range?

350-550 mV

Go to Step 5

Go to Step 6

The HO2S may be detecting a lean exhaust condition. Inspect 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

•	Inaccurate MAF sensor

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