What it means
This code indicates a high voltage condition in the reductant purge control valve circuit. It does not identify an evaporative fuel-vapor system fault.
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 vent DEF lines back toward the tank, helping prevent freeze damage. The control module monitors the valve's electrical drive circuit and sets P20A3 when its voltage is higher than expected; the code alone does not prove a short to battery voltage.
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
- Check freeze-frame data and reductant-system status to establish when the high circuit reading occurred and whether valve A was commanded.
- Inspect the valve connector and harness for corrosion, damaged insulation, or a wire pinched against a power source.
- Use the wiring information to check for an unintended connection to power and verify continuity through the drive circuit.
- Measure circuit voltage at valve A and at the module during the specified command, comparing readings with the manufacturer's specification.
- If the wiring checks out, test the valve coil and control-module driver using the manufacturer's procedure.
Common fixes
- Repair wiring that is shorted to a power source in valve A's drive circuit.
- Clean corroded connector pins and restore secure terminal contact.
- Replace a damaged connector or pinched wire.
- Replace purge valve A if its coil fails the manufacturer's test.
- Repair the control module driver if testing confirms it is faulty.
Can I keep driving?
The vehicle may remain operable, but valve A may not purge the DEF lines correctly at shutdown, raising freeze-damage risk in cold weather. Arrange diagnosis soon and prioritize repair 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.