P040F
EGR Temperature Sensor A/B Correlation
EGR / emissions
Generic OBD-II
Medium
What it means
P040F means the two EGR (exhaust gas recirculation) temperature sensors, A and B, disagree by more than the ECM allows. One sensor is likely reading incorrectly, often due to a wiring fault, a failing sensor, or carbon affecting its readings. It's an emissions-system fault that rarely changes how the car drives but should be repaired to keep EGR working and pass emissions testing.
Medium
Can I keep driving? Safe to keep driving in the short term — this is an emissions monitor fault, not a running problem — but it will fail an emissions test and should be repaired.
Common symptoms
What you'll notice
- Check-engine light on
- Usually no noticeable change in how the car drives
- Possible pinging or hesitation under load in some cases
- Failed or incomplete EGR emissions monitor
Common causes
Most likely first
- Faulty EGR temperature sensor A or BLikely
- Wiring or connector fault at one of the EGR temperature sensorsCommon
- Carbon buildup skewing one sensor's temperature readingCommon
- Stuck or restricted EGR flow affecting the readingsLess often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and compare the two EGR temperature sensor readings.
- Inspect both sensor connectors and wiring for damage or corrosion.
- Check the EGR passages and valve for carbon buildup or restriction.
- Test each sensor's resistance/response against spec to find the odd one out.
- Replace the faulty EGR temperature sensor; clear and re-test.
FAQ
Quick answers
Is it safe to drive with P040F?+
Yes, generally. It's an emissions-monitor correlation fault, so the car usually drives normally, but it should be fixed to pass emissions and keep the EGR system accurate.
Can I just clear P040F?+
It returns once the ECM compares the two sensors again. Repair the sensor or clean the EGR path first.
Related codes
Often seen with P040F
Read & clear P040F yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX