P0401: Exhaust Gas Recirculation (EGR) Flow Insufficient Detected

Symptoms

• Pinging or knocking under load
• Rough idle or stalling
• Failed emissions test
• Slight loss of power

Common causes

• Carbon-clogged EGR valve or passages
• Stuck EGR valve
• Faulty DPFE or EGR position sensor
• Failed EGR vacuum solenoid
• Blocked EGR tube

What to do?

Remove and inspect the EGR valve - carbon buildup is the most frequent cause and often cleanable. Check the EGR passages in the intake manifold and clean them out as well. Test the DPFE or position sensor against spec before replacing the valve itself.