U02A2 code meaning
Lost Communication With Reductant Quality Module
Network system Generic code U02xx codes Check engine light
What U02A2 means
The reductant quality module tells the engine or dosing controller whether the tank holds proper diesel exhaust fluid; in many trucks it is one tank sensor unit with level and temperature. U02A2 means its messages have stopped. Ford's 2023 diesel summary allows 5 s without them. In TSB 19-2315 Ford blames water in connectors C3613 and C4851 of the reductant harness on the 6.7 L F-Super Duty of model years 2017-2019 and replaces harness, pump and heater assembly or tank. Hino's SB-15-030 for 2014 and 2015 trucks points to a faulty DEF tank sensor assembly and supplies a more robust one. Mack lists software faults, missing supply and the connector. CARB 1968.2 requires every input of the inducement strategy to be monitored, so the warning sequence that leads to a speed limit may begin.
U02A2 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 4 hours
- Clears after repairAfter a drive cycle
Symptoms of U02A2
- MIL and DEF system warning
- Countdown to speed or restart limitation
- DEF quality and level readings missing
Common causes of U02A2
- Most likelyWater in the reductant harness connectors at tank or pump
- PossibleDefective DEF tank sensor unit with quality sensor
- PossibleMissing supply voltage or wrong software version of the module
- Less likelyDamaged CAN wiring between tank sensor and controller
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Reductant quality moduleVehicle bus wiring
What each part of U02A2 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| A2 | The exact fault in that area. |
What to do next
- Note U02A2 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 U02A2
What does U02A2 mean?
U02A2 means "Lost Communication With Reductant Quality Module". The reductant quality module tells the engine or dosing controller whether the tank holds proper diesel exhaust fluid; in many trucks it is one tank sensor unit with level and temperature. It is a generic code, so it means the same on every make.
Is it safe to drive with U02A2?
Drive gently and only to a workshop. With U02A2 the car can go into limp mode (reduced power) to protect itself.
Will U02A2 fail an emissions test?
Yes, it can. U02A2 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 U02A2 to fix?
Difficulty: medium. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will U02A2 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.