DTC P0420: Catalyst System Efficiency Below Threshold (Bank 1) Or DTC P0430: Catalyst System Efficiency Below Threshold (Bank 2): Notes

WARNING: This page is about a different car, the 2003 Lexus GS 300. However, it is still accessible from the selected car via links, so may be relevant.

CAUTION: If ECM replacement is instructed in following testing, always ensure ECM harness connector and ground circuit are okay. If either are suspect, repair and repeat testing to confirm ECM malfunction. If ECM is replaced, ECM must be programmed with proper ignition key code for engine immobilizer system. For programming procedures, see COMPUTER RELEARN PROCEDURES - LEXUS article in GENERAL INFORMATION.

NOTE: For information on engine immobilizer system, see COMPUTERIZED ENGINE CONTROLS in THEORY & OPERATION article.