EGR · Severity: Moderate
P0401 — Exhaust Gas Recirculation Flow Insufficient
The ECU detects less EGR flow than commanded.
Common symptoms
- Engine light
- Pinging under load
- Higher NOx emissions
Likely causes
- Carbon-clogged EGR valve or passages
- Blocked EGR cooler
- Faulty EGR valve position sensor
- Vacuum supply fault
First test to run
Command the EGR valve with a scan tool and compare desired vs. actual position and MAF change.
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