P0401
EGR Flow Insufficient
medium
i Description
The Exhaust Gas Recirculation (EGR) system is not flowing enough exhaust gas back into the intake manifold. The EGR reduces combustion temperatures to lower NOx emissions.
? Common Causes
- Carbon build-up blocking EGR passages
- Stuck-closed EGR valve
- Blocked EGR tube
- Faulty EGR vacuum solenoid
- Faulty DPFE sensor (Ford)
! Symptoms
- Check engine light
- Failed emissions test
- Engine pinging/knocking under load
- Slight increase in NOx emissions
# Diagnostic Steps
- Remove and inspect EGR valve for carbon build-up
- Clean EGR passages in intake manifold
- Test EGR vacuum solenoid
- Check DPFE/EGR pressure sensor
- Manually apply vacuum to EGR — engine should stumble at idle
⚙ Typical Fix
Clean the EGR valve and passages. Replace the EGR valve if stuck.
Parts Needed
EGR valve, EGR gasket, Carbon cleaner
Estimated Cost
$100-$400
↔ Related Codes
Q Frequently Asked Questions
Yes. Driveability is usually unaffected. The main issue is emissions — you will fail a smog test. Pinging under heavy load is possible.
Yes. Removing and cleaning the EGR valve is a common DIY job. Clean the intake passages too — carbon build-up is usually the cause.
Cleaning: $50-$100 if DIY. New EGR valve: $80-$300 plus labour.
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