OBD-II code · Powertrain (generic)
P040F EGR Temperature Sensor A/B Correlation
EGR temperature sensors A and B disagree by more than the allowed tolerance over a drive cycle. EGR mixes inert exhaust into intake to lower combustion peak temperature — too little raises NOx, too much causes misfires and rough running.
Is it safe to drive with P040F?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyOne sensor drifts
Symptoms
- Check engine light on
- Pinging or knocking under load
- Power loss and hesitation
- Possible rough idle
- Failed emissions inspection (NOx)
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Often, with basic tools
- Typical labour
- 0.5–2 h
- Emissions test
- Likely to fail
- Parts involved
- Egr Temperature Sensor
Related codes
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.