P20D5: Exhaust Aftertreatment Fuel Injector B Stuck Open

The second exhaust fuel doser (B) keeps passing fuel after it has been told to shut. No manufacturer documents P20D5 publicly; for the single doser A, Volvo and Mack trace the equivalent code P20CF to the fuel supply or the dosing module, and Ram fixed it on Cummins pickups with software. Detection usually relies on pressure in the doser feed line not rising again after closing, or on unexplained heat across the catalyst. Raw diesel in a hot catalyst can overheat it and causes smoke and fuel smell. CARB requires such injection faults to be caught. The stuck-closed counterpart is P20D6.

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
White smoke or fuel smell
Higher fuel consumption

Most likely causes

Deposits keeping doser B from sealing
Upstream shutoff valve leaking fuel through
Calibration error in the control software

What to check, in order

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

Check the connector and wiring of the injector indicated
Check the continuity of the wire between the component and the control module.
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 P20D5 means

P: Powertrain: engine and transmission
2: Generic code: same on every make
0: Subsystem depends on the code range
D5: Specific fault in that system

Frequently asked questions

Can I keep driving with code P20D5?

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 P20D5?

The most common causes are: deposits keeping doser B from sealing; upstream shutoff valve leaking fuel through; calibration error in the control software.

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.