What it means
DEF pump A control line stuck high — short to B+. 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 through the SCR emissions system. The module monitors the pump control circuit and sets this code when its signal stays above the expected range, which can occur if the control wire is shorted to battery supply.
Common causes
Most likely first.
- Short to B+
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
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 and live pump command information to confirm when the pump A circuit reads high and note any DEF warnings.
- Inspect the pump A harness for pinching or damaged insulation where it could contact a power wire or other supply.
- Check connector seals and terminals for water ingress, corrosion, or a pushed-back pin.
- With the circuit safely accessible, wiggle the harness while monitoring the signal for a change during the fault.
- Test the control wire for a short to supply and check continuity against the manufacturer's specification.
Common fixes
- Repair pump A wiring pinched against a power source.
- Replace or repair a damaged connector and restore its seal.
- Reseat or replace a pushed-back or corroded terminal.
- Repair the shorted control wire identified by circuit testing.
Can I keep driving?
The vehicle may remain drivable initially, but DEF dosing and NOx control can be affected, and some vehicles 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.