What it means
The exhaust aftertreatment fuel supply control is not performing as expected. The code alone does not identify whether the cause is a pump, restriction, or another component.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The exhaust aftertreatment fuel supply system delivers fuel for hydrocarbon dosing during DPF regeneration. The control module checks whether the commanded supply performs as expected, and sets P20D8 when its performance does not match the monitored conditions; the code alone does not identify which part is at fault.
Common causes
Most likely first.
- Weak or failing aftertreatment fuel pump
- Restricted fuel line or filter
- Faulty pressure or flow sensor
- Damaged wiring or poor electrical connection
Symptoms
- Check-engine light on
- DPF regeneration may be delayed or incomplete
- Reduced engine power in some vehicles
How to diagnose it
- Read freeze-frame data and aftertreatment live data to see when the supply performance fault occurred and whether a regeneration was being requested.
- Check the aftertreatment fuel pump, lines, filter, and connectors for damage, leaks, contamination, or restricted flow.
- Use a scan tool to compare commanded supply operation with available pressure or flow readings during the applicable test or regeneration conditions.
- Check the pressure or flow sensor readings for plausible changes as the pump is commanded on and off.
- Test pump power, ground, wiring continuity, and connector condition against the manufacturer's specification before condemning the pump or sensor.
Common fixes
- Repair a loose or corroded pump or sensor connector.
- Repair damaged wiring or poor electrical connections in the aftertreatment fuel supply circuit.
- Replace a restricted fuel filter or clear a restricted line.
- Replace a faulty pressure or flow sensor after confirming its circuit is sound.
- Replace a weak aftertreatment fuel pump after verifying its supply and control circuits.
Can I keep driving?
You can often drive cautiously if the engine runs normally, but avoid prolonged high-load use because regeneration may be delayed or incomplete. Continued operation can increase soot loading and may lead to reduced power.
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.