What it means
The control line driving DEF pump A is open — no continuity through the motor or harness, dosing pressure cannot be built.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Reductant pump A circulates DEF through the diesel exhaust fluid dosing system so the SCR system can reduce NOx emissions. The module monitors the pump control circuit and sets this code when it detects an open circuit and cannot establish the commanded pump operation.
Common causes
Most likely first.
- Pump motor winding open
- Open wire to pump
- Pin pushed back out of connector body
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
- Read freeze-frame data and emissions-system messages to determine whether the fault appeared during a pump command and check for a DEF countdown.
- Inspect the pump A connector for a backed-out pin, corrosion, moisture, or a loose connection.
- Trace the pump wiring for breaks or damage, especially where the harness is exposed to heat or movement.
- With power isolated as directed by the manufacturer's procedure, check circuit continuity from the module to pump A.
- Test the pump motor winding against the manufacturer's specification to distinguish an open motor from an open harness.
Common fixes
- Seat the backed-out terminal and secure the pump A connector.
- Repair an open or damaged wire in the pump control circuit.
- Clean or replace corroded connector terminals and restore the seal.
- Replace reductant pump A if its motor winding is open.
Can I keep driving?
The vehicle may remain drivable initially, but DEF dosing and NOx control can be disabled, and some vehicles start a no-start countdown. Check the dashboard warnings and arrange repair promptly; do not ignore a countdown.
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.