Code Definition

P0422 — Main Catalyst Efficiency Below Threshold (Bank 1)

System: Powertrain  |  Type: Generic (OBD-II Standard)  |  Make: Generic

About P0422

P0422 is a generic (obd-ii standard) powertrain diagnostic trouble code. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P0422 is stored, the module has detected a signal or supply voltage lower than the expected operating range; and a bank-specific fault, meaning it applies only to one cylinder bank of a multi-bank engine.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

Because P0422 is a generic OBD-II code, its base definition is shared across manufacturers. The specific diagnostic steps, reference values, and repair procedures can vary by vehicle, and the TaT Diagnostic Assistant includes verified procedures submitted by working technicians.

Code Information

The powertrain control module (PCM) sets P0422 when it detects that the main catalytic converter on Bank 1 is not functioning efficiently enough to reduce emissions. This is determined by monitoring the oxygen sensors before and after the catalyst. If the post-catalyst sensor signal closely mirrors the pre-catalyst sensor, it indicates insufficient conversion of exhaust gases, triggering the fault.

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