P04D9Closed Loop EGR Control At Limit - Flow Too Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- Exhaust gas recirculation (EGR) routes part of the exhaust back into the intake to lower combustion temperature and NOx. P04D9 means the EGR control has used up its authority and still gets too little flow – CARB requires this to be detected. Ford's 6.7-litre diesel sets it when the desired minus the measured EGR rate stays above 50 points for 20 s. Volvo cars from 2022 also set it after long low-load driving and fix it with a software update and an activation drive; a Mack/Volvo truck bulletin traces it to wrong EGR temperature readings from worn connector contacts.
- What you may notice
- Check engine light on
- Often no noticeable symptoms
- Higher NOx, petrol engines may knock
- Likely causes
- LikelyEGR cooler, valve or pipes sooted or narrowed
- PossibleEGR valve sticking or not opening fully
- PossibleEGR rate mismeasured (temperature sensor contacts, air mass meter, pressure sensor)
- RareSoftware or driving profile with long low-load operation
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €150 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.