What it means
DEF tank temperature sensor A reads above upper plausibility — open signal or short to B+. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The reductant tank temperature sensor measures DEF/AdBlue temperature so the control module can manage tank heating and reductant availability. P205D sets when the signal is higher than the expected range, which can result from an open signal wire or a short to battery voltage.
Common causes
Most likely first.
- Open signal line
- Connector pins corroded - high contact resistance
- Supply wire pinched against B+ source
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
- Record freeze-frame data and compare the reported tank temperature with ambient conditions and other temperature readings.
- Inspect the tank sensor connector and harness for an open or damaged signal wire, corrosion, water ingress, or a conductor pinched against a power source.
- Check for loose or pushed-back connector terminals and verify that the plug is fully seated.
- Use the wiring diagram to test the signal circuit for an open or unintended connection to battery voltage, following the manufacturer's procedure.
- If the circuit is intact, test the tank temperature sensor against the manufacturer's specification.
Common fixes
- Repair an open or damaged sensor signal wire.
- Reroute wiring pinched against a power source and repair damaged insulation.
- Clean or repair corroded or loose connector terminals.
- Replace the tank temperature sensor if it fails the specified test.
Can I keep driving?
You can generally drive if the vehicle has no other symptoms, but the system may interpret the DEF/AdBlue tank as warmer than it is and manage heating incorrectly. Watch for emissions warnings or a start countdown, since continued driving may eventually lead to a no-start restriction.
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.