P20DB: Exhaust Aftertreatment Fuel Supply Control Stuck Open
Do not keep driving
Stop driving the vehicle and have it recovered. This valve is the safety shut-off for fuel going into the exhaust, and with it stuck open that protection is gone.
Do not park over grass, leaves or anything flammable, and do not leave the engine running unnecessarily. Raw diesel in a hot exhaust is a genuine fire risk.
Mention any smell of unburnt diesel, smoke, or an unusually hot smell from underneath.
Ask for the exhaust fuel injector to be checked in the same visit, not just this valve. The two parts back each other up — this valve failing only becomes dangerous if the injector is leaking too — so checking both is what establishes whether anything was actually at risk and whether the particulate filter survived.
What this code means
The valve controlling fuel supply to the exhaust aftertreatment injector is stuck open.
This is the upstream half of the same danger its sibling describes, and the distinction is worth drawing because it decides which part is at fault. The injector meters fuel into the exhaust; this valve controls whether fuel reaches the injector at all.
That shut-off exists precisely as a safety measure. It is the second line of defence: if the injector leaks, closing the supply stops fuel reaching it. With this valve stuck open, that protection is gone — and if the injector is also passing, nothing at all is stopping fuel entering the exhaust.
Treat this exactly as seriously as a stuck injector. Raw diesel in a hot exhaust melts particulate filters and starts fires, and this code says the mechanism designed to prevent that has failed.
Stop driving and have the vehicle recovered.
The causes are ordinary for a valve in a hot, dirty location: fuel varnish or carbon holding it open, a failed solenoid, or a short to voltage keeping it energised. A driver stage failed on inside the module does the same thing.
Ask for the injector to be inspected in the same visit. These two parts protect each other, and a stuck-open supply valve is only dangerous when the injector also leaks — so establishing the state of both is what determines whether the vehicle was actually at risk.
Likely causes
Start here
- Faulty exhaust aftertreatment fuel injector · moderate
- Stuck exhaust fuel supply valve · moderate
Less common
- Wiring shorted to voltage · moderate
- Corroded or loose connector · easy
Rare
- Failed control module output driver · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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