Car symptom
EGR fault / stumble at cruise
A sticking or clogged EGR valve causes a stumble at light throttle, rough idle and pinging - often with a P0401/P0402 code.
Most likely causes
- Carbon-blocked EGR valve
- EGR pressure / position sensor
- Blocked EGR passages
- Intake carbon build-up
Checks to run
- Scan for EGR codes
- Inspect the valve for carbon
- Check the pressure/position sensor
Tools you may need
OBD-II scanner
Confirm before replacing. These are hypotheses to check — never buy parts on a guess. If the fault involves brakes, airbags or fuel under pressure, use a professional.
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FAQ
It depends on the cause. Some causes are cheap and quick; others (like a head gasket or seized caliper) need attention soon. Work through the checks in order and confirm before replacing parts.
Start with the free checks listed here. If they involve high voltage, fuel under pressure, airbags or brakes, let a professional handle it.
The interactive diagnostic asks targeted questions to narrow it down, and every cause must be confirmed with a measurement — never guess.