DTC P0420 Or P0430: Three-Way Catalyst Function: Procedure
- Visually inspect exhaust system for damage or leaks. Start engine and run at idle. Check for exhaust leak in front of three-way catalyst. Check for intake air leak after MAF sensor. Repair or replace faulty components as necessary and retest system. If no problems exist, go to next step.
- Check ignition timing, closed throttle position switch idle position adjustment and target idle speed. See ON-VEHICLE ADJUSTMENTS article. Adjust, if necessary and retest system. If no adjustments are necessary, go to next step.
- Turn engine off and turn ignition on. Measure voltage between ground and ECM terminals No. 101, 102, 103, 104, 105 and 107 by backprobing. See Figure and Figure . If battery voltage exists at each terminal, go to next step. If battery voltage does not exist at all terminals, repair appropriate injector or circuit and retest system. See SYSTEM & COMPONENT TESTING article.
- Turn ignition off. Remove ignition coils from rocker covers. Connect a known-good spark plug to coil and ground spark plug end. Crank engine and check for spark. If spark exists at all coils, go to next step. If spark does not exist at all coils, diagnose fault in coil or coil circuit and retest system. See DTC P1320: IGNITION SIGNAL .
- Turn ignition off. Remove injector assembly, keeping fuel hose and all injectors connected. Turn ignition on. Verify fuel is not dripping from any injectors. Replace any injectors from which fuel is dripping and retest system. If all injectors are okay, go to next step.
- Problem may be intermittent. Attempt to recreate conditions present when DTC was set. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article. If no problems are found, replace three-way catalyst and retest system.