U05A5Invalid Data Received From NH3 Sensor
- Generic OBD-II code · Network
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- An ammonia (NH3) sensor behind the SCR catalyst tells the controller whether too much urea is dosed and ammonia slips through. Like NOx sensors it carries its own electronics and talks over CAN; Bosch even offers NOx sensors that add a selective ammonia signal. U05A5 means the ammonia data come in but fail validation. FCA's bulletin 18-028-16 for 2014 Ram 3500 to 5500 Cab Chassis with the 6.7 L Cummins shows a special case: two ECM calibrations exist, with and without the ammonia sensor, and if U05A5 or U12A4 appears after the update, the wrong one was loaded. CARB 1968.2 requires a monitoring plan for such other exhaust gas sensors. U02A4 means the sensor is silent. Dosing control loses its slip feedback.
- What you may notice
- Check engine light on
- Code appears right after an engine software update
- SCR dosing runs without ammonia feedback
- Likely causes
- LikelyEngine calibration does not match the sensor fit (with or without NH3 sensor)
- PossibleAmmonia sensor control unit faulty
- RareDamaged wiring or connector at the ammonia sensor
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €80 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.