P20D1 Exhaust Aftertreatment Fuel Injector B Control Circuit/Open

Injector B is a second exhaust fuel doser, found only on layouts with two dosing points, for example twin exhaust paths. This code reports a broken control line or open coil on that second unit. No manufacturer documents P20D1 publicly; the logic would mirror injector A, where GM's diesel tables look for an off-state output voltage stuck in a mid band (P20CB, Type B). CARB wants every electrical part of an in-exhaust injection system covered by the comprehensive component checks. Most single-doser engines never set it, and many car diesels heat the filter by late in-cylinder injection instead of a doser at all.

Likely causes

Symptoms

• Check engine light on
• Regeneration incomplete on the affected exhaust path

Repair estimate

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

Parts involved

Related codes

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