What it means
Exhaust Aftertreatment Fuel Injector B Control Circuit Low: the control-circuit voltage is below the expected range. 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 doses fuel into the exhaust to raise its temperature during DPF regeneration, not to fuel the engine. P20D3 sets when injector B’s control-circuit voltage falls below the expected range, which can result from a short to ground, damaged wiring, or a poor connection.
Common causes
Most likely first.
- Short to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- Check engine light on
- Possible exhaust smoke or fuel odor during regeneration
- DPF regeneration may be impaired
How to diagnose it
- Save freeze-frame data and review injector B command and regeneration status to determine when the low-circuit condition occurred.
- With the exhaust cool, inspect injector B’s harness for chafing, exposed conductor, or contact with grounded metal.
- Check injector B’s connector terminals for corrosion, looseness, or signs of water entry.
- Using the wiring diagram, test injector B’s control wire for a short to ground and check continuity to the control module.
- If the harness passes, test injector B and its control circuit against the manufacturer’s specification.
Common fixes
- Repair chafed injector B wiring that is shorting to ground.
- Clean or repair corroded or loose terminals at injector B’s connector.
- Repair an open or damaged section of injector B’s control circuit.
- Replace injector B if it fails testing to the manufacturer’s specification.
Can I keep driving?
A short trip may be possible if the vehicle behaves normally, but avoid extended driving because injector B may not support DPF regeneration and soot loading can increase. Stop if heavy smoke or a strong fuel odor appears.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.