P20D9 Exhaust Aftertreatment Fuel Supply Control Circuit Low

For the fuel supply valve feeding the exhaust doser, the control line reads too low, which points to a short to ground. Volvo and Mack store P20D900 and, in AHI troubleshooting guide KC-2157, group it with the other electrical faults of the AHI module: check the module's connector and wiring harness. Depending on whether the valve is switched on its high or low side, a grounded line can either hold it shut or let it open unasked; most systems then disable dosing to be safe. The open circuit is P20D7 and the short to power P20DA. Valve sticking without an electrical cause is reported separately as P20DB or P20DC.

Likely causes

Symptoms

• Check engine light on
• Dosing disabled, no active regeneration

Repair estimate

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

Parts involved

Related codes

References: static.nhtsa.gov, law.cornell.edu.