What it means
DEF pump A control line stuck low — short to ground. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
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 for the SCR emissions system. The module monitors its control circuit and sets this code when the circuit signal stays below the expected range, commonly because the wire is shorted to ground.
Common causes
Most likely first.
- Short to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
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
- Check freeze-frame data and live pump command information to confirm when the pump A circuit reads low and whether DEF warnings are present.
- Inspect pump A wiring for chafing through the insulation, especially at clips, bends, and points where the harness touches the vehicle.
- Check the connector seal and terminals for water ingress, corrosion, or a pushed-back pin.
- With the circuit safely accessible, wiggle the harness while monitoring the signal to look for a change during the fault.
- Test the control wire for a short to ground and check its continuity against the manufacturer's specification.
Common fixes
- Repair chafed pump A wiring that is contacting ground.
- Dry, clean, or replace a water-damaged connector and restore its seal.
- Reseat or replace a pushed-back or corroded terminal.
- Repair an open or damaged section of the pump control wire identified by circuit testing.
Can I keep driving?
The vehicle may remain drivable initially, but DEF dosing may stop and the emissions system may start a no-start countdown. Arrange repair promptly and follow any countdown warning.
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.