P20D4 Exhaust Aftertreatment Fuel Injector B Control Circuit High

On the second exhaust fuel doser (B), the control line sits at or near battery voltage, so the driver cannot pull it low to open the valve. No manufacturer documents P20D4 publicly. For injector A, GM's diesel tables flag excess current in the switched-on state as a short to power and rate it Type B (P20CE). With doser B out of action, the share of the exhaust it serves no longer gets enough heat for regeneration. CARB requires circuit monitoring for every electronic part of an in-exhaust injection system. For the same doser, P20D1 covers a broken line and P20D3 a grounded one.

Likely causes

Symptoms

• Check engine light on
• Regeneration impaired, soot load rising

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.