P20D2: Exhaust Aftertreatment Fuel Injector B Control Performance

With its wiring intact, the second exhaust fuel doser (B) is not delivering what was asked for: too little heat appears across the catalyst during dosing, or heat appears when it should be idle. No manufacturer documents P20D2 publicly. The comparable check for injector A on GM's 6.6 L Duramax (P20CC, 15OBDG09) watches for the catalyst outlet running far hotter than its inlet outside regeneration. CARB requires a malfunction whenever the injection system can no longer bring about regeneration, and a feedback-control fault if the system runs out of adjustment. Stuck positions of doser B are P20D5 and P20D6, the electrical faults P20D1, P20D3 and P20D4.

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
Longer or more frequent regenerations
Higher fuel consumption

Most likely causes

Partly coked nozzle on doser B
Low or unstable fuel pressure feeding doser B
Exhaust temperature sensor reading wrong

What to check, in order

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

Check the connector and wiring of the injector indicated
Compare the reading with other engine data while varying the engine speed.
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 P20D2 means

P: Powertrain: engine and transmission
2: Generic code: same on every make
0: Subsystem depends on the code range
D2: Specific fault in that system

Frequently asked questions

Can I keep driving with code P20D2?

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 P20D2?

The most common causes are: partly coked nozzle on doser B; low or unstable fuel pressure feeding doser B; exhaust temperature sensor reading wrong.

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.