P20CF: Exhaust Aftertreatment Fuel Injector A Stuck Open
Do not keep driving
Stop driving the vehicle and have it recovered. This fault means raw diesel is being sprayed into the exhaust continuously and nothing is controlling it.
This is a genuine fire risk, not a precaution. Do not park over grass, leaves, or anything flammable, and do not leave the engine running while you make arrangements.
Expect a strong smell of unburnt diesel from the exhaust, and possibly smoke. Both fit this fault.
Ask for the particulate filter to be inspected as well as the injector. Uncontrolled fuel raises exhaust temperature far above the normal regeneration target, which can melt the filter — so the injector may not be the only part needing attention, and it is a fair question to ask up front.
What this code means
The exhaust aftertreatment fuel injector is stuck open, putting raw diesel into the exhaust continuously.
This is one of the most serious codes in the corpus, and the reason is fire.
Some diesels burn off their particulate filter using a dedicated injector in the exhaust rather than by injecting extra fuel into the cylinders. It is often called the seventh injector. It sprays a metered amount of diesel ahead of the oxidation catalyst, which burns it and raises exhaust temperature to around 600°C for a regeneration.
Stuck open means that spray is continuous and unmetered.
The consequences escalate quickly. Exhaust temperature rises far beyond the regeneration target, which melts the particulate filter substrate. Unburned diesel pools in the exhaust and can ignite. And a vehicle parked over dry grass with an exhaust at these temperatures is a genuine fire risk rather than a theoretical one.
Treat this as a stop-driving fault. Not because the engine will fail, but because the exhaust is being fed fuel that nobody is controlling.
The cause is almost always the injector itself — carbon and fuel varnish holding the needle off its seat, or a failed solenoid. These injectors live in exhaust heat and coke up, which is ordinary rather than exceptional.
A driver stage failed on will do the same thing electrically, so the wiring should be checked; but the injector is the likelier answer by a wide margin.
Likely causes
Start here
- Faulty exhaust aftertreatment fuel injector · moderate
- Leaking exhaust aftertreatment fuel injector · moderate
Less common
- Coked exhaust aftertreatment fuel injector · moderate
- Wiring shorted to voltage · moderate
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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