P20D6: Exhaust Aftertreatment Fuel Injector B Stuck Closed

What it means

Exhaust Aftertreatment Fuel Injector B Stuck Closed: the control module has detected this fault condition. This injector doses fuel into the exhaust to raise temperature for diesel particulate-filter regeneration; it does not fuel the engine.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

Aftertreatment fuel injector B meters fuel into the exhaust to help heat the DPF during regeneration; it does not fuel the engine. P20D6 means the control module detected injector B staying closed when fuel was required, preventing the exhaust from receiving the expected heat for regeneration.

Common causes

Most likely first.

1. Injector stuck closed
2. Carbon or debris buildup preventing free movement
3. Component wear with age - mechanical play

Symptoms

• Check engine light on
• DPF regeneration may be disrupted

How to diagnose it

1. Record freeze-frame data and check whether regeneration was requested or active when injector B failed to respond.
2. Inspect injector B’s connector and harness for loose terminals, corrosion, or damage that could interrupt operation.
3. With the exhaust cool, check injector B’s nozzle area for visible deposits or blockage.
4. Use a supported scan-tool actuator test to see whether injector B responds to a command, if available for the vehicle.
5. If the circuit checks pass, test injector B for sticking or blockage according to the manufacturer’s procedure.

Common fixes

• Repair a loose, corroded, or damaged injector B connection.
• Clean injector B if carbon or debris blocks its movement and cleaning is permitted by the manufacturer.
• Replace injector B if it remains closed or fails the specified functional test.
• Correct any contamination source contributing to injector B blockage.

Can I keep driving?

A short, gentle drive may be possible if the vehicle runs normally, but continued use can increase DPF soot loading because regeneration may not complete. Avoid repeated attempts to force regeneration until injector B is diagnosed.