What it means
The reductant purge control valve A drive circuit is open — used to evacuate DEF lines back to the tank when the engine is shut down to prevent freezing damage.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Reductant purge valve A opens at shutdown to let DEF drain from the delivery lines back toward the tank, reducing the risk of freeze damage. The control module monitors the valve's electrical drive circuit, and P20A0 sets when that circuit is open and the valve cannot be driven as expected.
Common causes
Most likely first.
- Solenoid winding open
- Pin pushed back out of connector body
- Cracked solder joint inside the module or sensor
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 any reductant-system messages, then use scan data or an available output command to confirm whether valve A is being requested to operate.
- Inspect valve A's connector for a backed-out pin, corrosion, or a poor fit, and check the harness for breaks or damage.
- Check the valve coil and circuit continuity using the wiring information and compare results with the manufacturer's specification.
- Check power and control wiring between valve A and the control module, including terminals at both ends, to locate the open circuit.
- If the wiring is intact, test the valve coil and module output using the manufacturer's procedure.
Common fixes
- Reconnect a loose plug or restore a pushed-back terminal at purge valve A.
- Repair a broken wire or poor connection in the valve drive circuit.
- Replace purge valve A if its winding is open.
- Repair the control module connection or module fault if testing confirms the open is there.
Can I keep driving?
The vehicle may continue to run, but the lines may not purge at shutdown, raising the risk of DEF freezing and damaging the delivery system in cold weather. Have the fault addressed promptly, especially before freezing conditions.
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.