Code Definition

P0423 — Heated Catalyst Efficiency Below Threshold (Bank l)

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

About P0423

P0423 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 P0423 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 P0423 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 P0423 when it detects that the heated catalytic converter on Bank 1 is not achieving the required efficiency. Heated catalysts contain an integrated heating element to reach operating temperature quickly, improving emissions control during cold starts. The PCM monitors the oxygen sensors before and after the catalyst to determine its efficiency. If the post-catalyst sensor signal does not show expected conversion activity, the fault is triggered.

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