P0432 - Main Catalyst Efficiency Below Threshold (Bank 2)
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
The Engine Control Unit (ECU) monitors the catalytic converter's efficiency by comparing signals from the upstream (pre-cat) and downstream (post-cat) oxygen sensors. A healthy catalyst stores oxygen, resulting in a steady output from the downstream sensor (approx. 0.45V - 0.7V). If the downstream sensor begins to mimic the rapid rich-to-lean oscillations of the upstream sensor (cycling between 0.1V and 0.9V), it indicates the catalyst substrate is failing to effectively reduce emissions like NOx, CO, and HC. P0432 specifically refers to Bank 2. The monitor typically runs during steady-state cruising conditions once the system has reached operating temperature.
Possible Causes
Failed Three-Way Catalytic Converter (Bank 2)
Exhaust leak near or upstream of the catalyst
Faulty downstream Oxygen Sensor (Bank 2, Sensor 2)
Engine coolant temperature (ECT) sensor fault or long-term fuel trim imbalances
Symptoms
Recommended Solution
Workflow
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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