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P codepowertrainMedium severity

P20D7Exhaust Aftertreatment Fuel Injector "B" Stuck Closed

The second ("B") exhaust aftertreatment fuel injector is not delivering fuel when commanded open, so active DPF regeneration cannot raise exhaust temperature.

Definition

During active regeneration the ECM commands the "B" hydrocarbon doser injector to spray fuel ahead of the DOC and expects a corresponding rise in DOC-outlet temperature and a characteristic fuel-pressure response. P20D7 sets when the injector is commanded open but the expected temperature or pressure change never occurs, indicating the injector is mechanically stuck closed or plugged. Regenerations fail or abort, the MIL illuminates, soot accumulates in the DPF, and the engine will eventually set restriction codes and derate.

Common causes

  • Doser injector tip coked/plugged with carbon from exhaust exposure
  • Injector pintle mechanically seized closed
  • Blocked or kinked fuel supply line to the injector
  • Failed or stuck-closed aftertreatment fuel supply valve starving the injector
  • Debris from contaminated fuel lodged in the injector
  • Insufficient supply pressure from the dosing fuel circuit

Common misdiagnoses

  • DPF replaced for soot loading caused by the non-functional doser
  • DOC condemned for failing to light off when it never received fuel
  • EGT sensors replaced for correctly reporting no temperature rise
  • ECM replaced when the fault is mechanical at the injector

Troubleshooting steps

  1. 1.Verify the electrical command reaches the injector

    Confirm with a scope or noid-style test that the driver pulses the injector during a commanded regen; a good signal shifts diagnosis to fuel delivery or the injector itself.

  2. 2.Check dosing fuel supply pressure

    Compare supply pressure at the injector against spec during commanded dosing; low pressure implicates the supply valve, lines, or pump rather than the injector.

  3. 3.Remove and inspect the injector tip

    Heavy carbon coking on the nozzle is the classic failure; some OEMs allow cleaning, otherwise replace the injector.

  4. 4.Flow-test the injector

    Command the injector with supply pressure applied and verify a proper spray pattern into a graduated container per the service procedure.

  5. 5.Run a forced regeneration to confirm the repair

    Verify DOC-outlet temperature climbs into the regeneration target range (typically 550-650 C) and the regen completes without aborting.

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