P040DEGR Temperature Sensor A Circuit High
- 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
- EGR temperature sensor A measures the gas temperature in the EGR path – for cooler monitoring, component protection and the EGR model. Whether it sits before or after the cooler depends on the maker: GM diesels have sensor A after and B before the cooler, Ford diesels sensor B after it. Like a coolant sensor it is an NTC, so a low voltage means hot. P040D means the signal is above its upper limit – very cold or, far more often, an open circuit (connector off, broken wire). Thresholds: GM's Duramax LML above 4.84 V for 5 s, GM 2014 above 4.98 V, GM 2018 a resistance above 1268 Ω (40 of 50 samples, MIL after two trips); Ford diesel lists the code without figures. A substitute value is used.
- What you may notice
- Check engine light on
- Usually no change in driving
- Substitute value used, EGR cooler check suspended
- Likely causes
- LikelyConnector off, broken wire or open circuit
- PossibleSensor open internally
- PossibleGround wire open or short to positive
- RareEngine module input
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €50 – €250
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.