What it means
Exhaust Aftertreatment Fuel Injector B Control Circuit High: the control-circuit voltage is above 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 sprays fuel into the exhaust to help heat the DPF during regeneration; it does not fuel the engine. P20D4 means the control module detected injector B’s control-circuit voltage above the expected range, often because the circuit is shorted to battery power or has excessive resistance at a connection.
Common causes
Most likely first.
- Short to B+
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
Symptoms
- Check engine light on
- Possible exhaust smoke or fuel odor during regeneration
- DPF regeneration may be impaired
How to diagnose it
- Record freeze-frame data and check regeneration status and injector B command data to see when the high-circuit fault occurred.
- With the exhaust cool, inspect injector B’s connector and harness for corrosion, damaged insulation, or a wire pinched against a power source.
- Check injector B’s terminals for looseness or corrosion that could increase circuit resistance.
- Using the wiring diagram, test injector B’s control wire for a short to battery voltage and check continuity to the control module.
- If wiring and connections pass, test injector B and its control circuit against the manufacturer’s specification.
Common fixes
- Repair damaged wiring that is contacting a power source.
- Clean or repair corroded or loose injector B connector terminals.
- Repair a short to battery power in injector B’s control circuit.
- Replace injector B if it fails testing to the manufacturer’s specification.
Can I keep driving?
If the vehicle runs normally and there is no smoke or fuel odor, a short trip to a repair location may be possible, but avoid prolonged driving because DPF regeneration may be impaired. Stop if heavy smoke or a strong fuel odor develops.
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.