Powertrain, generic (extended)

P20CD Exhaust Aftertreatment Fuel Injector A Control Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

Here the control line of the hydrocarbon doser has a short to ground. GM's diesel tables 18OBDG04 and 25OBDG04A test the output while the driver is off: if the voltage drops below about 2 V, the line is touching ground. GM rates it Type A, which lights the MIL after one trip, and the fault only clears after a calibrated count of good tests or a control-module reset. The LML/LGH Duramax lists it as Type B. A grounded line can make the doser open whenever its supply side is switched on, so fuel may enter the exhaust uncontrolled; that is why it is treated more strictly than the open circuit (P20CB) or the short to power (P20CE).

Likely causes

Control wire chafed through against the frame or exhaust
Water or salt in the doser connector bridging to ground
Internal short in the doser solenoid

Symptoms

  • Check engine light on after a single trip
  • Doser disabled, no active regeneration
  • Possible fuel smell or smoke from the exhaust

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

P20CBP20CEP20D3P2699

References: gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com.