What causes a P0623 code?

P0623 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 P0623 code?

Drivability depends on the severity. Check the severity rating and verified driver reports on this page before continuing to drive with P0623 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

P0623

Generator Lamp Control Circuit Malfunction

What it means

The engine control module (ECM) provides a ground to verify the alternator/generator warning lamp circuit. This code triggers when the ECM detects an open circuit, short to ground, or short to voltage in the warning lamp circuit.