What it means
A general circuit fault on the AdBlue tank cap switch - reports whether the cap is properly closed.
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 reports whether the AdBlue/DEF tank cap is closed, helping the control module monitor the tank’s closure status. This code sets when the switch circuit has a general electrical fault and the module cannot reliably determine the cap state.
Common causes
Most likely first.
- Open or short in cap switch wiring
- Faulty cap switch
- Loose or corroded connector
- Cap switch not registering cap movement correctly
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 reductant-system live data for the cap-switch status recorded when the fault set.
- Confirm the cap is correctly fitted, then inspect the cap switch, tank-area connector, and wiring for damage, looseness, moisture, or corrosion.
- Open and close the cap while observing live switch status to see whether the signal changes consistently.
- Using the wiring diagram, test the switch circuit for opens or shorts and check connector terminal condition.
- If the wiring and connection pass, test the cap switch against the manufacturer’s specification and replace it if it fails.
Common fixes
- Fit the cap correctly and clear debris that prevents its switch from being actuated.
- Reconnect or clean the cap-switch connector and repair damaged wiring.
- Replace a faulty reductant tank cap switch.
- Correct cap or switch alignment if it prevents reliable switch operation.
Can I keep driving?
Driving is usually possible if there are no other faults, but the warning may progress to an AdBlue/DEF countdown that can eventually prevent restarting. Resolve the switch fault promptly and keep the reductant system properly filled.
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.