U05A5 code meaning
Invalid Data Received From NH3 Sensor
Network system Generic code U05xx codes Check engine light
What U05A5 means
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.
U05A5 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.3 to 2 hours
- Clears after repairAfter a drive cycle
Symptoms of U05A5
- Check engine light on
- Code appears right after an engine software update
- SCR dosing runs without ammonia feedback
Common causes of U05A5
- Most likelyEngine calibration does not match the sensor fit (with or without NH3 sensor)
- PossibleAmmonia sensor control unit faulty
- Less likelyDamaged wiring or connector at the ammonia sensor
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Nh3 sensor
What each part of U05A5 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| A5 | The exact fault in that area. |
What to do next
- Note U05A5 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U05A5
What does U05A5 mean?
U05A5 means "Invalid Data Received From NH3 Sensor". An ammonia (NH3) sensor behind the SCR catalyst tells the controller whether too much urea is dosed and ammonia slips through. It is a generic code, so it means the same on every make.
Is it safe to drive with U05A5?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will U05A5 fail an emissions test?
Yes, it can. U05A5 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is U05A5 to fix?
Difficulty: medium. A typical repair takes 0.3 to 2 hours of work. This is a job for a workshop.
Will U05A5 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.