OBD-II code · Powertrain (generic, extended)
P24E7 NH3 Sensor Heater Circuit Low
The heater control circuit of the ammonia (NH3) slip sensor reads below the expected voltage range. Either the wiring is shorted to ground or the heater driver in the SCR/dosing module is stuck low. The sensor element never warms up, NH3 readings stay invalid and the SCR strategy falls back to open-loop dosing.
Is it safe to drive with P24E7?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyHeater control wire shorted to ground
- PossibleInternal short across the heater element
- Less likelyLow-side driver pulled down in the control module
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.6–2 h
- Emissions test
- Likely to fail
- Parts involved
- Nh3 Sensor Heater, Heater Driver, Sensor Wiring
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.