What it means
The control line that gates the DEF supply pump or the regeneration heating circuit does not respond as commanded — duty cycle, current draw, or response time off-spec.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The reductant supply control circuit operates the DEF supply pump or a related regeneration heating function, depending on vehicle design. The control module compares the commanded circuit operation with its electrical response and timing. P202F sets when that response is outside the expected range or performance.
Common causes
Most likely first.
- Reductant supply or regeneration control circuit fault
- Open or high-resistance wiring or connection
- Control component fault
Symptoms
- Check engine light or NOx warning on
- AdBlue/DEF level or quality warning
- Possible no-start countdown after ignore period
- Failed emissions inspection (NOx)
How to diagnose it
- Check freeze-frame data and live reductant supply or regeneration-control status to identify whether the code occurred during pump operation or a heating command.
- Inspect the relevant control circuit wiring and connectors for looseness, corrosion, heat damage, or chafing, using the vehicle wiring information to identify the circuit.
- Check related fuses and power and ground connections for the reductant supply or regeneration control component.
- Test the circuit for opens, shorts, and excessive resistance between the control module and the named component, following the manufacturer's wiring procedure.
- Compare commanded operation with circuit current or feedback using scan-tool data and the manufacturer's specification to isolate wiring from a failed control component.
- Clear the code after repair and verify that the commanded supply or regeneration function responds as expected.
Common fixes
- Clean and secure a loose or corroded control-circuit connector.
- Repair an open, chafed, or high-resistance wire in the reductant supply or regeneration control circuit.
- Replace a failed reductant supply or regeneration control component after circuit tests confirm the component is at fault.
- Repair a poor power or ground connection to the controlled component.
Can I keep driving?
You may be able to drive, but DEF delivery or an associated regeneration function may not work correctly, affecting emissions control. Heed DEF and NOx warnings because a starting restriction may follow if the issue remains unresolved.
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.