What it means
This code indicates a low voltage condition in the exhaust aftertreatment fuel supply control circuit.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The aftertreatment fuel supply control circuit operates the fuel delivery used for exhaust hydrocarbon dosing during DPF regeneration. The module monitors the circuit's electrical level and sets P20D9 when it detects a voltage lower than expected, which can result from a short to ground or excess resistance in the connection or wiring.
Common causes
Most likely first.
- Short to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- Check-engine light on
- DPF regeneration may be delayed or incomplete
- Reduced engine power in some vehicles
How to diagnose it
- Check freeze-frame data and fault status to determine when the circuit-low condition was recorded and whether it is current or intermittent.
- Inspect the aftertreatment fuel supply control wiring and connectors for chafing, water intrusion, corrosion, loose pins, or pin push-back.
- With the circuit monitored on a scan tool, gently move the harness near the pump or control component to see whether the reading or fault status changes.
- Check the circuit for a short to ground and measure voltage drop across suspect connectors while the circuit is commanded, following the manufacturer's test procedure.
- If the wiring and connections pass, test the control component and its driver circuit against the manufacturer's specification.
Common fixes
- Clean and secure corroded or loose control-circuit connector pins.
- Repair chafed wiring that is shorting to ground.
- Repair a damaged connector or replace terminals with poor contact.
- Replace a failed aftertreatment fuel supply control component only after confirming the circuit and module command.
Can I keep driving?
If the vehicle runs normally, cautious short trips may be possible, but avoid relying on it for demanding work because DPF regeneration may be delayed or incomplete. Stop driving if power drops sharply or the engine begins running abnormally.
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.