P040CEGR Temperature Sensor A Circuit 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
- 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. P040C means the signal is below its lower limit – very hot or a signal wire shorted to ground. Thresholds: GM's Duramax LML below 0.46 V for 5 s, GM 2014 below 0.14 V, GM 2018 a resistance below 404 Ω, Ford diesel below 0.69 V for 5 s; MIL after two trips. A substitute value is used and the EGR cooler check is suspended.
- What you may notice
- Check engine light on
- Usually no change in driving
- Substitute value used, EGR cooler check suspended
- Likely causes
- LikelySignal wire shorted to ground (chafed on the exhaust)
- PossibleSensor shorted internally
- PossibleWater in the connector
- RareActual extreme gas temperature (EGR cooler faulty)
- 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.