P20D6: Exhaust Aftertreatment Fuel Injector B Stuck Closed

The second exhaust fuel doser (B) fails to deliver fuel even though the control unit commands it open. No manufacturer documents P20D6 publicly. For doser A, Volvo and Mack handle the matching code P20D0 by checking the dosing module and replacing the nozzle, whose tip tends to clog with carbon; the same weak spot applies to B. A blocked doser means the catalyst stays too cool for regeneration, so soot keeps accumulating in the filter until power is cut back. CARB requires a malfunction once the injection system cannot achieve regeneration. Stuck open on the same doser is P20D5.

Medium severity. Can I keep driving?Drive as little as possible and go to a repair shop. If you smell fuel or the engine is shaking badly, do not keep driving.

Symptoms

Check engine light on
Failed or frequent regenerations
Reduced power once the filter is heavily loaded

Most likely causes

Clogged nozzle tip on doser B
No fuel reaching doser B because of a blocked line or closed supply valve
Mechanically seized valve in doser B

What to check, in order

Start with the simplest. You can tick off each step.

Check the connector and wiring of the injector indicated
Use the scanner to command the movement and compare the actual position with the requested one.
Measure the resistance and compare it with the manufacturer's specification
Check the control signal with an oscilloscope; on direct injection or diesel engines, leave this to a repair shop because of the high voltages
On diesels, check the per-cylinder injection corrections

Good to know

Repair difficulty: hard
It can trigger limp mode.
It affects emissions.

What each character of P20D6 means

P: Powertrain: engine and transmission
2: Generic code: same on every make
0: Subsystem depends on the code range
D6: Specific fault in that system

Frequently asked questions

Can I keep driving with code P20D6?

Drive as little as possible and go to a repair shop. If you smell fuel or the engine is shaking badly, do not keep driving.

What causes code P20D6?

The most common causes are: clogged nozzle tip on doser B; no fuel reaching doser B because of a blocked line or closed supply valve; mechanically seized valve in doser B.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.