P0131
DTC P0131: Primary HO2S (Sensor 1) Circuit Low Voltage1. Reset the ECM.
2. Start the engine. Hold the engine at 3,000 rpm with no load (in neutral) until the radiator fan comes on.
3. Check the primary HO2S (Sensor 1) output voltage with a scan tool or the HDS during acceleration using wide open throttle.
Does the voltage stay at 0.5 V or less?
YES - Go to step 4.
NO - Intermittent failure, system is OK at this time. Check for poor connections or loose terminals at the primary HO2S (Sensor 1) and at the ECM.
4. Check the fuel pressure.
Is it normal?
YES - Go to step 5.
NO - Repair the fuel supply system.
5. Turn the ignition switch OFF.
6. Disconnect the primary HO2S (Sensor 1) 4P connector.
7. Start the engine and let it idle.
8. Check the primary HO2S (Sensor 1) output voltage with a scan tool or the HDS.
Does it stay at 0.5 V or less?
YES - Go to step 9.
NO - Replace the primary HO2S (Sensor 1).
9. Turn the ignition switch OFF.
10. Disconnect the ECM connector C (31P).
11. Check for continuity between primary HO2S (Sensor 1) 4P connector terminal No. 1 and body ground.
Is there continuity?
YES - Repair short in the wire between the ECM (C16) and the primary HO2S (Sensor 1).
NO - Substitute a known-good ECM and recheck. If the symptom/indication goes away, replace the original ECM.