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