What does code U02A4 mean?

Q: What does code U02A4 mean?

Lost Communication With NH3 Sensor. U02A4 is a generic communication fault indicating that one or more control modules on the vehicle's controller area network (CAN) bus have lost contact with the ammonia (NH3) sensor, which is used on diesel vehicles to monitor selective catalytic reduction (SCR) system performance. The computer detects this when the module responsible for the sensor stops receiving expected periodic messages or voltage signals from the NH3 sensor circuit, often after a set number of missed messages or an out-of-range signal.

DTC codes / U02xx · Lost communication with a control module / U02A4

U02A4Lost Communication With NH3 Sensor

U02A4 is a generic communication fault indicating that one or more control modules on the vehicle's controller area network (CAN) bus have lost contact with the ammonia (NH3) sensor, which is used on diesel vehicles to monitor selective catalytic reduction (SCR) system performance. The computer detects this when the module responsible for the sensor stops receiving expected periodic messages or voltage signals from the NH3 sensor circuit, often after a set number of missed messages or an out-of-range signal.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaLost communication with a control module

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.