DTC P0138 or P0158. Saturn L300/LW300 2005

For 1990-2009 cars only

Makes 🢒 Saturn 🢒 2005 🢒 L300/LW300 🢒 DTC 🢒 DTC P0138 or P0158

Engine Controls Component Views
Engine Controls Schematics

Circuit Description

The heated oxygen sensor (HO2S) produces a voltage that varies between 100-900 mV under normal operating conditions. The engine control module (ECM) produces a bias voltage on the HO2S signal circuit of 420-480 mV. The reference ground for the sensor is provided through the ECM. The ECM monitors the signal voltage to determine if the exhaust is lean or rich. The oxygen sensor voltage is high when the exhaust is rich, and low when the exhaust is lean. The ECM constantly monitors the HO2S signal during the closed loop operation. If the ECM forces a lean status and detects a HO2S voltage that is not responding to the commanded lean state, or if the ECM detects a HO2S voltage that stays below a specified value, DTC P0138 will set for bank 1 sensor 2 or DTC P0158 will set for bank 2 sensor 2.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

•	DTC P0138 HO2S Circuit High Voltage Bank 1 Sensor 2

•	DTC P0158 HO2S Circuit High Voltage Bank 2 Sensor 2

Conditions for Running the DTC

•	The engine is running.

•	The ECT parameter is more than 4°C (40°F).

•	The Battery Voltage parameter is more than 10.5 volts.

•	The calculated catalytic converter temperature is less than 800°C (1,472°F).

•	The above conditions have been met for more than 90 seconds.

•	DTC P0138 and P0158 runs continuously once the above conditions are met.

Conditions for Setting the DTC

•	The ECM detects that the HO2S parameter is more than 1.2 volts for longer than 5.1 seconds.

•	The ECM detects that the HO2S parameter is stuck above 350 mV for more than 110 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.

Step

Action

Values

Yes

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Controls Connector End Views or Engine Control Module Connector End Views

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

Operate the engine at normal operating temperature.
Quickly cycle the throttle from closed throttle to wide open throttle 3 times while observing the affected HO2S parameter with a scan tool.

Does the affected HO2S voltage react instantly to the above action?

Go to Step 3

Go to Step 4

Observe the Freeze Frame/Failure Records for this DTC.
Turn OFF the ignition for 90 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 4

Go to Intermittent Conditions

Turn OFF the ignition.
Disconnect the affected heated oxygen sensor (HO2S).
Turn ON the ignition, with the engine OFF.
Observe the affected HO2S voltage parameter on a scan tool.

Is the voltage within the specified range?

425-525 mV

Go to Step 7

Go to Step 5

Measure the voltage from the HO2S high signal circuit, on the engine harness connector, to a good ground. Refer to Circuit Testing in Wiring Systems.

Is the voltage more than the specified value?

475 mV

Go to Step 9

Go to Step 6

Measure the voltage from the HO2S low signal circuit, on the engine harness side, to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems.

Is the voltage more than the specified value?

25 mV

Go to Step 10

Go to Step 15

Connect a 3-amp fused jumper wire between the HO2S high signal circuit, on the engine harness side, and a good ground.
Observe the HO2S voltage parameter with a scan tool.

Is the voltage less than the specified value?

25 mV

Go to Step 8

Go to Step 11

Remove the jumper wire from the previous step.
Connect a 3-amp fused jumper wire between the HO2S high signal circuit and the HO2S low signal circuit, on the engine harness side.
Observe the HO2S parameter with a scan tool.

Is the voltage less than the specified value?

25 mV

Go to Step 13

Go to Step 12

Test the HO2S high signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 18

Go to Step 15

Test the HO2S low signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 18

Go to Step 15

Test the HO2S high signal circuit for an open or for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 18

Go to Step 15

Test the HO2S low signal circuit for an open or for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 18

Go to Step 15

The HO2S 2 is detecting a rich exhaust condition or may be contaminated. Inspect for one of the following conditions:

•	HO2S connector water intrusion

•	A silicon-contaminated HO2S 2

•	Fuel-contaminated engine oil

•	Incorrect fuel pressure--Refer to Fuel System Diagnosis .

•	A leaking fuel pressure regulator--Refer to Fuel System Diagnosis .

•	Rich fuel injectors--Refer to Fuel System Diagnosis .

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

Did you find and correct the condition?

Go to Step 18

Go to Step 14

Inspect for poor connections at the harness connector of the HO2S sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 18

Go to Step 16

Inspect for shorted terminals and poor connections at the harness connector of the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 18

Go to Step 17

Replace the affected HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 .

Did you complete the replacement?

Go to Step 18

Replace the ECM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the replacement?

Go to Step 18

Clear the DTCs with a scan tool.
Turn OFF the ignition for 90 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

Go to Step 2

Go to Step 19

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK