P20D8Exhaust Aftertreatment Fuel Supply Control Circuit/Open
An open or fault has been detected in the control circuit for the valve that supplies fuel to the exhaust aftertreatment dosing system.
Definition
Diesel exhaust aftertreatment dosing systems use an ECM-controlled fuel supply valve (shutoff valve) to feed and isolate the line that carries diesel fuel to the hydrocarbon doser injector. P20D8 sets when the ECM detects an open circuit or general fault in that valve's control circuit, leaving it unable to reliably open or close the dosing fuel supply. Active DPF regeneration is disabled while the fault is present, the MIL illuminates, and continued operation leads to soot accumulation, DPF restriction codes, and a possible derate.
Common causes
- Open circuit from a broken wire or connector terminal in the valve harness
- Corroded or backed-out terminals at the supply valve connector
- Failed valve solenoid coil (open winding)
- Blown fuse or open feed circuit to the valve
- Failed ECM driver circuit
Common misdiagnoses
- Doser injector replaced when the supply valve circuit is the fault
- DPF cleaned or replaced for soot buildup that followed the failed regens
- Fuel pump condemned for a dosing-circuit electrical fault
- ECM replaced without checking harness continuity
Troubleshooting steps
1.Check power at the supply valve connector
Verify battery voltage on the feed circuit with the key on; no voltage points to a fuse or feed-wiring problem.
2.Measure the valve solenoid resistance
Compare coil resistance to the OEM specification; an open (OL) reading confirms a failed solenoid.
3.Verify control-circuit continuity to the ECM
With connectors disconnected, confirm near-zero ohms end-to-end on the control wire and no short to ground or power.
4.Command the valve with a bidirectional scan tool
Listen or feel for the valve clicking when toggled; a good circuit with no actuation confirms the valve, while no driver activity with good wiring implicates the ECM.
5.Repair and confirm with a forced regeneration
Verify dosing pressure builds when commanded and the regeneration completes without the code resetting.