What it means
The control module monitors the reductant tank cap switch signal as the cap is opened and closed. It sets this code when the signal is within an electrical range but does not respond as expected.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The reductant tank cap switch tells the control module when the AdBlue/DEF cap is opened or closed. This code sets when the electrical signal is within a plausible range but does not change or behave as expected as the cap moves.
Common causes
Most likely first.
- Worn or sticking cap switch
- Poor switch adjustment or cap alignment
- Loose or corroded connector
- Intermittent wiring 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 and reductant-system live data to see what cap-switch state was reported when the fault occurred.
- Inspect the tank cap, switch actuator, and alignment for wear, sticking, or a cap that does not fully engage the switch.
- Open and close the cap while watching live switch status to check that the signal changes each time.
- Inspect the connector and wiring for corrosion, looseness, or damage, then flex the harness while monitoring the signal for intermittent changes.
- Test switch operation and alignment against the manufacturer’s procedure, and test the circuit if switch movement does not produce a consistent response.
Common fixes
- Correct cap or switch alignment so the cap reliably actuates the switch.
- Clean or repair a sticking cap-switch mechanism if serviceable.
- Repair a loose, corroded, or intermittent connector or wire.
- Replace a worn cap switch that responds inconsistently.
Can I keep driving?
The vehicle may remain driveable, but the reductant warning can lead to an AdBlue/DEF countdown and eventual no-start if left unresolved. Check the cap is secure and arrange repair 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.