What causes a P0423 code?

P0423 can be triggered by several issues — see the verified probable causes and step-by-step diagnostics shared by mechanics and owners on OBDIY.

Can I drive with a P0423 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P0423 active.

Follow the step-by-step diagnostic on this page, then read the verified fixes contributed by other Heavy Truck owners — the answer marked "Verified Cause" worked for the original poster.

OBDIY

OBD-II

P0423

P0423 Heated Adsorption Catalyst Efficiency Below Threshold

What it means

The Engine Control Module (ECM) has detected that the heated catalyst system's efficiency has dropped below the minimum acceptable level for Bank 1. This system uses a heater to bring the catalyst to operating temperature faster to reduce cold-start emissions.