P0143

DTC P0143: Third HO2S (Sensor 3) Circuit Low Voltage-'02-03 M/T Models

1. 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. Test-drive under following conditions.
- 55 - 65 mph (89 - 105 km/h) steady speed
- Transmission in 4th or 5th gear
- Until the readiness code or Temporary DTC P0143 and/or P0143 is set

4. Check for a Temporary DTC with the scan tool.

Is Temporary DTC P0143 and/or P0143 indicated?

YES - Go to step 6.

NO - Go to step 5.

5. Check the Third HO2S (Sensor 3) output voltage at 3,000 rpm with the scan tool.

Does the voltage stay at 0.3 V or less?

YES - Go to step 6.

NO - Intermittent failure, system is OK at this time. Check for poor connections or loose wires at the Third HO2S (Sensor 3) and at the ECM.

6. Turn the ignition switch OFF.
7. Disconnect the Third HO2S (Sensor 3) 4P connector.
8. Start the engine.
9. Check the Third HO2S (Sensor 3) output voltage with the scan tool.

Does the voltage stay at 0.3 V or less?

YES - Go to step 10.

NO - Replace the Secondary HO2S (Sensor 2), and the Third HO2S (Sensor 3).

10. Turn the ignition switch OFF.
11. Disconnect ECM connector C (31P).




12. Check for continuity between the Third HO2S (Sensor 3) 4P connector terminal No.2 and body ground.

Is there continuity?

YES - Repair short in the wire between the ECM (C16) and the Third HO2S (Sensor 3).

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