P0432 — Catalyst System Low Efficiency Bank 2

Causes

• Failed or degraded catalytic converter (bank 2)
• Faulty downstream (post‑cat) oxygen sensor (bank 2 sensor 2)
• Faulty upstream (pre‑cat) oxygen sensor (bank 2 sensor 1)
• Exhaust leaks upstream of downstream O2 sensor
• Engine misfires, rich running, or unmetered fuel contamination
• Oil or coolant contamination of the converter

Symptoms

• Malfunction Indicator Lamp (MIL) / Check Engine Light illuminated
• Failed emissions test (high HC, CO)
• Reduced fuel economy
• Occasional reduced engine performance or hesitations if related to misfire
• Rotten egg (sulfur) or unusual exhaust smell if converter is failing

What to check

• Read freeze‑frame and mode 6 / OBD data to confirm conditions when code set
• Compare live data: bank 2 upstream (S1) vs downstream (S2) O2 sensor voltages and switching patterns
• Inspect exhaust system for leaks, damage, or restrictions upstream of downstream O2
• Check for related codes (misfire, fuel trim, MAP/MAF, injector faults)
• Perform fuel trim and short/long term trim analysis for evidence of rich/lean condition
• Inspect O2 sensor wiring, connectors and measure heater power/ground and sensor resistance

Signal parameters

• Bank 2 upstream O2 (Sensor 1) — typical narrow‑band: rapid switching ~0.1–0.9 V when closed‑loop
• Bank 2 downstream O2 (Sensor 2) — should be less active; a healthy converter reduces switching amplitude (downstream voltage relatively steady close to ~0.4–0.6 V depending on sensor type)
• Heater circuit resistance: typically low ohms (refer to vehicle spec) and should have battery voltage when key on
• Short‑term fuel trim (STFT) and long‑term fuel trim (LTFT) — large offsets (>±10%) indicate fueling issues
• Catalyst temperature delta — working converter often shows significant temp rise from inlet to outlet under load (varies by design; large or no delta is diagnostic)

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