Powertrain, generic · Auxiliary emission controls
P04D9 Closed Loop EGR Control At Limit - Flow Too Low
Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo
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.
Likely causes
EGR cooler, valve or pipes sooted or narrowed
EGR valve sticking or not opening fully
EGR rate mismeasured (temperature sensor contacts, air mass meter, pressure sensor)
Software or driving profile with long low-load operation
Symptoms
- Check engine light on
- Often no noticeable symptoms
- Higher NOx, petrol engines may knock
Repair estimate
DifficultyMediumWorkshop job
Parts and labour€150–1,500
Time1–5 h
Typical range across vehicles; the real cost depends on what the testing finds.
Parts involved
egr valveegr cooleregr controlengine control module
Related codes
References: fordservicecontent.com, static.nhtsa.gov, static.nhtsa.gov, law.cornell.edu.