What it means
Voltage on the reductant pump motor position sensor signal line is above the expected window. Wire shorted to B+ or sensor open.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
The reductant pump motor position sensor sends a signal to the engine control module so it can monitor pump position while delivering AdBlue/DEF. P2AD9 sets when that signal voltage is above its expected range, often because the signal is shorted to battery voltage or the sensor or its signal/ground circuit is open.
Common causes
Most likely first.
- Signal wire shorted to B+
- Open or high-resistance signal/ground circuit
- Position sensor fault
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 related reductant faults, then check live pump position data to confirm the signal is unusually high or fixed.
- Inspect the sensor connector and harness for damaged insulation, corrosion, fluid intrusion, or contact with a battery-voltage wire.
- Using the wiring diagram, check the signal line for a short to B+ and inspect the signal and ground circuits for opens or high resistance.
- Measure the signal and sensor supply and ground with suitable equipment, comparing results with the manufacturer's specification.
- If the wiring checks out, test the pump motor position sensor and replace it if it leaves the signal above specification.
Common fixes
- Repair a signal wire shorted to battery voltage or damaged harness insulation.
- Restore an open or high-resistance signal or ground connection.
- Replace the reductant pump motor position sensor if it is open or fails the manufacturer's specification.
- Clear the code and confirm the position signal responds normally to pump operation.
Can I keep driving?
The vehicle may drive at first, but the high position signal can prevent reliable reductant-pump control and impair NOx emissions treatment; an AdBlue/DEF warning may lead to a restart countdown. Arrange repair promptly and follow any countdown 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.