Note. Bank No. 1 refers to bank which includes cylinder No. 1. Bank No. 2 refers to bank without cylinder No. 1. Air/Fuel (A/F) sensor refers to sensor closest to engine block. Heated oxygen sensor No. 2 refers to sensor farthest from engine block.
Note. For component location, see appropriate illustration in THEORY & OPERATION article.
Circuit Description
ECM compares waveform of Air/Fuel (A/F) sensor (located before catalytic converter) with waveform of heated oxygen sensor No. 2 (located after catalytic converter) to determine if converter performance has deteriorated. If both waveforms change at similar rate, catalyst performance has deteriorated. DTC is set when A/F sensor and heated oxygen sensor No. 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 No. 2 circuit is open or shorted.
- Defective heated oxygen sensor No. 2.
- A/F sensor circuit is open or shorted.
- Defective A/F sensor.
Diagnostic Aids
Using scan tool, read freeze frame data. Freeze frame records engine conditions when malfunction is detected.