What it means
Reductant temperature sensor A reading is within electrical range but plausibility check fails — slow response or sticks at one value through a tank-warming cycle.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Reductant temperature sensor A measures DEF temperature for dosing and tank-heating control. P2043 sets when the signal remains electrically plausible but does not behave as expected, such as responding too slowly or failing to change as the tank warms.
Common causes
Most likely first.
- Sensor drifts or sticks
- Sensor element aged beyond calibration window
- Sensor mounting loose - signal damping
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
- Review freeze-frame data and live sensor A temperature to see whether its reading is stuck or changes implausibly during the recorded operating conditions.
- Compare the reading with ambient conditions and observe whether it responds during a normal tank-warming cycle.
- Inspect sensor A's connector, mounting, and harness for looseness, corrosion, damage, or a loose fit that could damp the temperature response.
- Check the sensor circuit for intermittent contact or resistance changes and compare results with the manufacturer's specification.
- If the circuit and mounting are sound, test reductant temperature sensor A for drift or a slow response against the manufacturer's specification.
Common fixes
- Secure the sensor A mounting if it is loose.
- Clean or repair a poor connector contact and repair damaged wiring.
- Replace reductant temperature sensor A if it sticks, drifts, or responds too slowly.
Can I keep driving?
A vehicle that runs normally may be driven cautiously for a short time, but do not leave the DEF or NOx warning unresolved. Incorrect temperature compensation can affect reductant dosing or tank heating and may lead to a no-start countdown or an emissions test failure.
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.