What it means
DEF pump A receives a run command but does not start, or shuts off prematurely — pump performance is below threshold.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Reductant pump A moves DEF through the dosing system to support SCR NOx reduction. The module monitors the commanded pump operation and sets this code when pump response is outside its expected range or performance, such as failing to start or stopping too soon.
Common causes
Most likely first.
- Pump motor seized — DEF crystallised inside pump head
- Motor brushes worn
- Carbon or debris buildup preventing free movement
Symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
How to diagnose it
- Review freeze-frame data, pump command information, and emissions warnings to see when pump A failed to respond as expected.
- Check DEF level and condition, then inspect pump A and its connections for leaks, damage, or visible crystallised DEF.
- Inspect the pump connector and wiring for loose or corroded terminals that could interrupt operation.
- Use the manufacturer's diagnostic procedure to command pump A and observe whether it runs consistently.
- If the electrical supply and control are sound, test the pump for restricted movement or internal failure against the manufacturer's procedure.
Common fixes
- Clean accessible DEF crystallisation from the pump area using the manufacturer's service guidance.
- Repair a poor pump A connector or damaged wiring causing intermittent operation.
- Replace reductant pump A if it is seized, worn, or fails the commanded-operation test.
- Correct contaminated or unsuitable DEF if inspection identifies it as the source of deposits.
Can I keep driving?
The vehicle may be drivable at first, but failed DEF dosing can raise NOx emissions and may trigger a no-start countdown. Avoid delaying repair, especially if a countdown or emissions warning is displayed.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.