P20D3: Exhaust Aftertreatment Fuel Injector B Control Circuit Low

The control line of the second exhaust fuel doser (B) is pulled toward ground. No manufacturer documents P20D3 publicly. For injector A, GM's diesel tables detect this by a switched-off output voltage below about 2 V and treat it as Type A with the MIL after one trip (P20CD), because a grounded line can open the valve without command. A similar strict rating is likely for B. CARB requires each electrical part of an in-exhaust injection system to be checked for circuit faults. The open circuit is P20D1, the short to power P20D4. Only engines with two dosing points can set this code.

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
Doser B switched off, regeneration impaired

Most likely causes

Chafed control wire to doser B touching ground
Moisture in the doser B connector
Internal short 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
With the connector unplugged, check whether the signal wire is making contact with ground.
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: medium
It can trigger limp mode.
It affects emissions.

What each character of P20D3 means

P: Powertrain: engine and transmission
2: Generic code: same on every make
0: Subsystem depends on the code range
D3: Specific fault in that system

Frequently asked questions

Can I keep driving with code P20D3?

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 P20D3?

The most common causes are: chafed control wire to doser B touching ground; moisture in the doser B connector; internal short 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.