P0403: OBD-II code P0403 means the PCM has detected an electrical fault in the EGR control circuit — the EGR valve isn't responding to commands from the PCM.

Symptoms

• Check engine light is on; NOx emissions rise and the engine may ping or knock under light load.
• Rough idle, hesitation on acceleration, or a slight power loss because EGR flow is stuck at the wrong position.
• The vehicle will fail an OBD-II emissions test until the EGR monitor completes and reports ready with no pending code.

Common causes

• A failed EGR valve solenoid with an open or shorted internal coil, so the valve won't move on command.
• Damaged wiring or a corroded connector between the EGR valve and the PCM.
• A carbon-clogged EGR valve mechanically stuck open or closed, preventing valid position feedback.

What to do?

Command the EGR valve open and closed with a scan tool and watch position feedback in live data. If the valve doesn't respond, verify power and ground at its connector. Replace the EGR valve if the solenoid tests open or shorted. Clean carbon deposits from the EGR passages after replacement.