What it means
DEF tank temperature sensor A reads below lower plausibility — short to ground. 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 for tank-heating and reductant-availability decisions. P205C sets when the sensor signal is lower than the expected range, often because the signal wire is shorted to ground or the connector is faulty.
Common causes
Most likely first.
- Short to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
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 compare the reported tank temperature with ambient conditions and other available temperature readings.
- With the code active, inspect the tank sensor harness and connector for chafing, water ingress, corrosion, or a terminal pushed back.
- Monitor live tank temperature while gently moving the harness to see whether the reading changes, and note any interruption.
- Use the wiring diagram to test the sensor signal for a short to ground and check connector continuity as specified by the manufacturer.
- If the wiring checks out, test the tank temperature sensor against the manufacturer's specification.
Common fixes
- Repair chafed wiring and secure it away from rubbing points.
- Dry, clean, or replace water-damaged or corroded connector terminals.
- Reseat a pushed-back terminal or repair a poor connection.
- Replace the tank temperature sensor if it fails the specified test.
Can I keep driving?
You can often drive cautiously if the vehicle runs normally, but the system may misread tank temperature and manage DEF/AdBlue heating incorrectly. In cold weather this can affect reductant availability; heed any emissions warning or start countdown to avoid a possible 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.