P0401: Exhaust Gas Recirculation (EGR) Flow Insufficient
Severity: Moderate
What it means
Not enough exhaust gas is flowing back into the engine through the EGR system.
Common symptoms
- Engine pinging under load
- Failed emissions test
Common causes
- Carbon-clogged EGR passages
- Faulty EGR valve
- Bad EGR sensor or vacuum supply
What to check first
- Inspect the EGR valve and passages for carbon buildup
Causes vary by vehicle. Confirm with testing before replacing parts.
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