What it means
Exhaust Aftertreatment Fuel Injector A 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
Exhaust aftertreatment fuel injector A doses fuel into the exhaust to raise temperature for DPF regeneration; it does not fuel the engine. The control module monitors injector A’s control-circuit voltage and sets P20CD when that voltage is below the expected range, often because the circuit is shorted to ground or has excessive resistance.
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
- Review freeze-frame data and DPF regeneration status, and check for other injector A or aftertreatment circuit codes.
- With the exhaust cool and the system powered down as directed by the manufacturer, inspect injector A’s connector and wiring for chafing, exposed conductors, corrosion, or damaged pins.
- Use the wiring diagram and manufacturer’s isolation procedure to test injector A’s control circuit for a short to ground.
- Check connector terminals and circuit joints for corrosion or poor contact that could create a voltage drop.
- If the harness and connections pass, test injector A and the control-module output against the manufacturer’s specification.
Common fixes
- Repair wiring chafed through to ground and secure the harness away from the exhaust.
- Clean or replace corroded or damaged injector A connector terminals.
- Repair damaged sections of injector A’s control circuit.
- Replace injector A or repair the module only if testing confirms the failed component.
Can I keep driving?
The engine may remain drivable, but injector A may not dose correctly and DPF regeneration can fail, allowing soot to build up. Avoid ignoring DPF warnings, and address smoke or fuel odor during regeneration promptly.
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.