Code
P24ED
Generic
P — Powertrain
NH3 Sensor Calibration Memory
AI status
Completed
Completed
100%
Causes
- Corrupted or erased calibration data in ECU/aftertreatment control module (EEPROM/FLASH)
- Incomplete or failed software update or reflash of the control module
- Battery disconnect, low battery voltage, or power interruption during memory write
- Incorrect or incompatible sensor or module part number installed
- Sensor replacement without performing required calibration/learn procedure
- Wiring or connector fault causing intermittent communication during calibration
Symptoms
- Malfunction Indicator Lamp (MIL) or warning lamp illuminated
- Reduced SCR control performance or ammonia slip control degraded
- Possible engine derate or reduced-emissions mode depending on vehicle
- Diagnostic trouble codes related to NH3/NH3 sensor or aftertreatment control
- NOx or NH3 concentration readings are out of expected range or inconsistent
What to check
- Read freeze frame and all stored DTCs with a capable scan tool; note related codes and events
- Check vehicle service history for recent ECU reflashes, updates, or battery disconnection
- Verify battery voltage and charging system health; check for recent power interruptions
- Inspect NH3 sensor connector and wiring for damage, corrosion, or poor pin contact
- Confirm correct NH3 sensor part number and software/firmware level of ECU/module
- Check CAN/bus communication status and look for communication-related codes
Signal parameters
- NH3 sensor raw output (mV or ppm) vs expected range
- Sensor heater current (mA) and heater voltage
- Sensor temperature or internal temp reading (°C)
- Calibration offsets/gains or stored calibration table presence flag
- ECU/aftertreatment module software/firmware version and calibration checksum
- CAN message presence and update rate for NH3 sensor and aftertreatment module
Diagnostic algorithm
- Retrieve P24ED and any related codes; record freeze frame and live data for NH3 sensor PIDs.
- Inspect wiring and connector for the NH3 sensor; repair any damage and clear corrosion/loose pins.
- Verify battery voltage is stable (12.4–14.8 V) and retry clearing the code; note if code returns.
- Check service records: if the sensor or module was recently replaced or ECU reflashed, confirm correct procedures were completed.
- Use a manufacturer-level scan tool to view calibration status/flags and to attempt the NH3 sensor calibration/relearn procedure per published steps.
- If calibration procedure fails or flags indicate corrupted memory, attempt ECU/module software reflash or calibration data re-installation using dealer/manufacturer tools.
- If reflashing and calibration repeatedly fail and wiring/sensor are confirmed good, consider module hardware fault; consult manufacturer for ECU repair or replacement.
- After repair or reflash, perform required aftertreatment functional checks and confirm no related codes return during road or functional test.
Likely causes
- Recent module reflash or software update that did not complete successfully
- Battery replacement or voltage drop during a calibration or programming event
- NH3 sensor was replaced but calibration/teach-in not performed
- ECU detected checksum or parameter mismatch for NH3 calibration table
- Intermittent CAN/bus communication during storage of calibration data
Fault status
Status
NH3 sensor calibration memory invalid/corrupted — check calibration data, ECU/software, and sensor installation.
Repair difficulty: Hard
Diagnostic time: 1.0-3.0 hours
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