DTC Troubleshooting: P0131 (1-1)

DTC P0131 (1-1):  HO2S Circuit Low Voltage

1.Reset the ECM/PCM.

2.Start the engine. Hold the engine at 3,000 rpm (min-1) with no load (in Park or neutral) until the radiator fan comes on.

3.Check the HO2S output voltage with the scan tool during acceleration using wide open throttle.

Does the voltage stay at 0.5 V or less?

YES - Go to 4.

NO - Intermittent failure, system is OK at this time. Check for poor connections or loose wires at the  HO2S and at the  ECM/ PCM.n

4.Check the fuel pressure.

Is it normal?

YES - Go to 5.

NO - Repair the  fuel supply system.n

5.Turn the ignition switch OFF.

6.Disconnect the HO2S 4P connector.

7.Turn the ignition switch ON (II).

8.Check the HO2S output voltage with the scan tool.

Does it stay at 0.5 V or less?

YES - Go to 9.

NO - Replace the  HO2S.n

9.Turn the ignition switch OFF.

10.Disconnect ECM/PCM connector A (31P).

11.Check for continuity between the HO2S 4P connector terminal No. 1 and body ground.


Is there continuity?

YES - Repair short in the wire between the ECM/PCM (A6) and the  HO2S.n

NO - Update the ECM/PCM if it does not have the latest software, or substitute a known-good ECM/PCM, then recheck. If the symptom/indication goes away with a known-good ECM/PCM, replace the original ECM/PCM.n