What it means
The reductant (AdBlue) tank or line heater driver does not switch as expected. AdBlue may freeze in cold weather, blocking SCR dosing.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The reductant heater driver controls heating for the diesel exhaust fluid (AdBlue/DEF) tank or lines so the fluid can flow in cold weather for selective catalytic reduction dosing. P263D sets when the driver does not switch as expected, which can leave the fluid frozen or prevent proper dosing and may lead to emissions warnings or a vehicle countdown.
Common causes
Most likely first.
- Aged driver shows degraded switching behaviour
- Heater element resistance drifted out of range
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
- Save freeze-frame data and check the ambient temperature and warning history to determine whether the heater fault appeared in conditions where reductant could freeze.
- Scan the aftertreatment system for heater, reductant temperature, level, quality, and dosing codes that may identify a related fault.
- Inspect the tank and line heater connectors and harness for damage, corrosion, fluid intrusion, or poor connections.
- Review scan-tool data for heater commands, reported temperatures, and any available current feedback to see whether the driver responds.
- Test the heater element and driver circuit against the manufacturer's procedure to distinguish an out-of-range element from a driver fault.
Common fixes
- Repair a loose, corroded, or damaged heater connector.
- Repair damaged reductant heater wiring or its ground connection.
- Replace a tank or line heater element confirmed to be outside the manufacturer's specification.
- Replace the heater driver only after the element and wiring tests pass.
Can I keep driving?
The vehicle may continue to run, but frozen reductant or failed dosing can raise NOx emissions and may trigger a no-start countdown after the permitted interval. Heed AdBlue/DEF and countdown warnings and arrange repair promptly, especially before cold weather.
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.