Powertrain, generic (extended)

P20CB Exhaust Aftertreatment Fuel Injector A Control Circuit/Open

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

The engine computer checks the drive line of the hydrocarbon doser, a separate valve that sprays diesel into the exhaust ahead of the oxidation catalyst so the particulate filter can be heated for regeneration. This code means an open circuit: GM's diesel tables 18OBDG04 and 25OBDG04A watch the voltage on the switched-off driver output and flag a reading stuck in a mid band of roughly 2 to 3 V (Type B, MIL after two trips); the 6.6 L Duramax LML/LGH (15OBDG09) compares commanded and actual driver state. Short to ground and short to power have their own codes (P20CD, P20CE). Some makers use P2697 for the same injector instead. Without the doser the engine cannot finish active regenerations, so soot builds up.

Likely causes

Corroded or loose connector at the doser, which sits under the vehicle in the exhaust area
Heat- or chafe-damaged wire between engine computer and doser
Open solenoid winding inside the doser
Faulty output stage in the engine control module

Symptoms

  • Check engine light on
  • Particulate filter regeneration does not start or is aborted
  • Soot load warning and, later, reduced engine power

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€100–900
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

aftertreatment fuel injector

Related codes

P20CDP20CEP20CCP20D1P2697P2463

References: gsi.ext.gm.com, gsi.ext.gm.com, law.cornell.edu.