P2AD8: Reductant Pump Motor Position Sensor Circuit Low

What it means

Voltage on the reductant pump motor position sensor signal line is below the expected window. Wire shorted to ground or sensor short.

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. P2AD8 sets when that signal voltage is below its expected range, commonly because the signal is grounded, the sensor is shorted, or the signal or ground circuit has excessive resistance or an open.

Common causes

Most likely first.

1. Signal wire shorted to ground
2. Position sensor fault
3. Open or high-resistance signal/ground circuit

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

1. Read freeze-frame data and related reductant faults, then check live pump position data to confirm the signal is unusually low or absent.
2. Inspect the sensor connector and harness for chafing, corrosion, fluid intrusion, or a signal wire contacting ground.
3. Using the wiring diagram, check the signal wire for a short to ground and inspect sensor power and ground connections for opens or high resistance.
4. Measure the signal circuit and sensor response with suitable equipment, comparing results with the manufacturer's specification.
5. If the wiring and connections pass, test the pump motor position sensor and replace it if it pulls the signal below specification.

Common fixes

• Repair a signal wire shorted to ground or damaged harness insulation.
• Restore an open or high-resistance signal or ground connection.
• Replace the reductant pump motor position sensor if its output is shorted or out of specification.
• Clear the code and confirm the position signal returns to a plausible range.

Can I keep driving?

The vehicle may drive at first, but the low position signal can disable 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.