What it means
Exhaust Aftertreatment Fuel Injector B Stuck Open: the control module has detected this fault condition. This injector doses fuel into the exhaust to raise temperature for diesel particulate-filter regeneration; it does not fuel the engine.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Aftertreatment fuel injector B adds fuel to the exhaust to raise temperature during DPF regeneration, rather than supplying the engine. P20D5 indicates the control module has detected injector B remaining open when it should close, which can send excess fuel into the exhaust and interfere with regeneration.
Common causes
Most likely first.
- Injector stuck open
- Carbon or debris buildup preventing free movement
- Component wear with age - mechanical play
Symptoms
- Check engine light on
- Possible excess exhaust smoke or fuel odor
- DPF regeneration may be disrupted
How to diagnose it
- Save freeze-frame data and review regeneration history and injector B command data to establish when the stuck-open condition was detected.
- With the exhaust cool, inspect injector B and the nearby exhaust for wet fuel, heavy deposits, or signs of leakage.
- Check injector B’s connector and wiring for damage or poor contact that could affect operation.
- Use a supported diagnostic actuator test, if available, to compare injector B’s commanded state with its response.
- If electrical checks pass, inspect injector B for carbon, debris, sticking, or wear according to the manufacturer’s procedure.
Common fixes
- Repair damaged wiring or poor connections at injector B.
- Clean injector B if deposits prevent it from closing and cleaning is permitted by the manufacturer.
- Replace injector B if it sticks open or fails the specified functional test.
- Address any underlying contamination contributing to injector B deposits.
Can I keep driving?
Avoid driving if excess smoke, a strong fuel odor, or signs of fuel entering the exhaust are present, because unburned fuel can overheat or damage aftertreatment parts. Arrange prompt diagnosis if the vehicle limits power or shows a regeneration 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.