P24ED
NH3 Sensor Calibration Memory
What it means
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?
The vehicle is usually drivable for short distances, but the problem can worsen or affect emissions. Diagnose and repair as soon as practical.
Most likely causes
New sensor installed but not coded/learned to the ECM
highOne of the most commonly reported causes for this code — check this first.
Corrupted calibration memory after voltage drop
mediumA plausible cause — test and verify before replacing parts.
Module software outdated, reflash may resolve
lowLess common, but worth ruling out after the more likely causes.
Related help
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