OBD-II code · Powertrain (generic, extended)
P24ED NH3 Sensor Calibration Memory
The NH3 slip sensor stores its individual calibration coefficients in non-volatile memory (EEPROM/flash). The ECM cannot read valid calibration values — either checksum fails, the memory is empty after replacement, or communication with the sensor electronics is broken. Without the trim values the raw ammonia reading is unreliable.
Is it safe to drive with P24ED?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyNew sensor installed but not coded/learned to the ECM
- PossibleCorrupted calibration memory after voltage drop
- Less likelyModule software outdated, reflash may resolve
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.3–1.5 h
- Emissions test
- Likely to fail
- Parts involved
- Nh3 Sensor, Sensor Eeprom
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.