| 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 article in GENERAL INFORMATION. |
Note. Bank No. 1 refers to bank which includes cylinder No. 1. Bank No. 2 refers to bank without cylinder No. 1. Heated oxygen sensor No. 1 refers to sensor closest to engine block. Heated oxygen sensor No. 2 refers to sensor farthest from engine block.
Circuit Description
ECM compares waveform of heated oxygen sensor No. 1 (located before catalytic converter) with waveform of heated oxygen sensor No. 2 (located after catalytic converter) to determine if catalytic converter performance has deteriorated. If both waveforms change at similar rate, catalytic converter performance has deteriorated. DTC P0420 is set when all heated oxygen sensor bank No. 1, sensors No. 1 and 2 waveforms have same amplitude after vehicle is driven for 5 minutes at 20-50 MPH. DTC P0430 is set when all heated oxygen sensor bank No. 2, sensors No. 1 and 2 waveforms have same amplitude after vehicle is driven for 5 minutes at 20-50 MPH. Possible causes are
- Defective catalytic converter.
- Heated oxygen sensor circuit is open or shorted.
- Defective heated oxygen sensor.
Diagnostic Aids
Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected.