P24DB: Reductant Purge Control Valve B Circuit Open

What it means

The secondary reductant purge valve B - which clears AdBlue from injector and lines at shutdown to prevent crystallisation - has an open control circuit.

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 is part of the system that clears AdBlue/DEF from the injector and lines during shutdown to help prevent crystallisation. P24DB sets when the control module detects an open electrical path in valve B's control circuit, so the valve may not operate when commanded.

Common causes

Most likely first.

1. Open or damaged wiring
2. Loose or corroded connector
3. Faulty reductant purge control valve

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. Record freeze-frame data and check for related reductant, NOx, or countdown warnings before clearing any codes.
2. Inspect the valve B connector for a loose fit, corrosion, moisture, or pushed-back pins.
3. Trace the valve B harness for a break, damaged insulation, or a disconnected section.
4. Use the wiring diagram to test continuity through the valve B control circuit and check its connections as specified by the manufacturer.
5. If the wiring and connector are intact, test the valve B coil or actuator against the manufacturer's specification.

Common fixes

• Reconnect and secure the valve B electrical connector.
• Clean corroded terminals or repair damaged connector pins.
• Repair an open or damaged section of valve B wiring.
• Replace reductant purge control valve B if its actuator fails the specified test.

Can I keep driving?

The vehicle may remain driveable, but the purge fault can trigger emissions warnings and, on some vehicles, a no-start countdown if ignored. Follow any countdown or AdBlue/DEF warning promptly and avoid delaying diagnosis.