What it means
The control module detected that reductant purge control valve B is stuck open. The code does not establish that reductant lines drain continuously.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Reductant purge control valve B helps clear AdBlue/DEF from the injector and lines during shutdown. P24DF sets when the control module detects that valve B remains open when its operation should indicate otherwise; the code alone does not prove the lines are continuously draining.
Common causes
Most likely first.
- Valve stuck open
- Carbon or debris buildup preventing free movement
- Component wear with age - mechanical play
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
- Record freeze-frame data and check related reductant and NOx codes for clues about when valve B was detected open.
- Inspect valve B's connector and wiring for damage that could affect the control or feedback signal.
- Check the valve and accessible passages for debris or deposits that could prevent the valve from seating, following the manufacturer's procedure.
- Use a supported scan-tool actuator test, if available, to compare valve B's commanded state with its observed response.
- If the circuit and passage are sound, test the valve for proper closing against the manufacturer's specification.
Common fixes
- Repair a loose connector or damaged valve B wiring.
- Remove contamination from the valve or passage if permitted by the service procedure.
- Restore free movement if valve B is serviceable and sticking.
- Replace reductant purge control valve B if it does not close as specified.
Can I keep driving?
The vehicle may still be driveable, but an improperly operating purge valve can affect reductant-system operation and trigger emissions warnings or a no-start countdown. Do not ignore a countdown or persistent AdBlue/DEF 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.