FixItFor.Us
P codepowertrainHigh severity

P20D6Exhaust Aftertreatment Fuel Injector "B" Stuck Open

The second ("B") exhaust aftertreatment fuel injector is delivering fuel when it is commanded closed, letting uncontrolled fuel into the exhaust stream.

Definition

The ECM verifies that the "B" hydrocarbon doser injector actually stops flowing when de-energized, typically by watching downstream exhaust gas temperatures and fuel-supply pressure behavior outside of regeneration events. P20D6 sets when evidence of fuel delivery appears while the injector is commanded off, meaning the injector is mechanically stuck or leaking. This is a serious condition: continuous raw fuel over the DOC can drive exhaust temperatures high enough to damage or melt the DOC and DPF, and symptoms can include white smoke, fuel odor, elevated EGTs, and reduced fuel economy along with the MIL.

Common causes

  • Doser injector stuck open or leaking from internal wear or debris on the seat
  • Coking/carbon deposits holding the injector pintle off its seat
  • Contaminated fuel or debris from an upstream supply-line failure
  • Control circuit shorted in a way that keeps the injector energized
  • Failed ECM driver holding the injector on

Common misdiagnoses

  • DOC or DPF replaced for overheating damage without fixing the leaking doser that caused it
  • EGT sensors replaced for the high readings they are correctly reporting
  • Turbocharger suspected for white exhaust smoke that is actually raw dosing fuel
  • Head gasket or injectors in the engine blamed for exhaust-side fueling

Troubleshooting steps

  1. 1.Confirm the injector is not electrically commanded on

    Verify with a meter or scope that the control circuit is de-energized when the scan tool shows zero commanded dosing; if it is energized, chase the electrical fault instead.

  2. 2.Watch EGTs with dosing commanded off

    A DOC-outlet temperature that climbs well above DOC-inlet during steady cruising with no regeneration active indicates fuel is still being delivered.

  3. 3.Isolate and inspect the injector for leak-through

    With supply pressure applied and the injector de-energized, check the nozzle for weeping or drips per the OEM leak-down procedure.

  4. 4.Check the fuel supply/shutoff valve

    Verify the aftertreatment fuel supply valve isolates pressure when closed, so the injector is not being force-fed during off periods.

  5. 5.Replace the stuck injector and inspect downstream damage

    After replacement, inspect the DOC face for wetting or thermal damage and run a forced regen to confirm normal temperature control.

Related codes