What it means
Reductant temperature sensor A reads above its upper plausibility limit — open signal or short to B+.
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 reports DEF temperature for dosing and tank-heating control. P2045 sets when the signal rises above the expected range, often because the signal circuit is open or shorted to battery voltage; the code does not establish that the fluid is actually hot.
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
- Review freeze-frame data and live sensor A temperature for an implausibly high reading while P2045 is active.
- Inspect sensor A's connector and harness for a disconnected plug, damaged or corroded terminals, broken signal wire, or wiring pinched against a power source.
- Check connector seating and terminal contact, then inspect the signal circuit for an open or short to battery voltage using the manufacturer's wiring information.
- Test circuit continuity and voltage under the conditions specified by the manufacturer to locate an open or unwanted power feed.
- If the circuit passes its checks, test reductant temperature sensor A against the manufacturer's specification.
Common fixes
- Reconnect the sensor A plug and repair loose or corroded terminals.
- Repair an open signal wire or wiring shorted to battery voltage.
- Replace reductant temperature sensor A if it fails the manufacturer's test with a sound circuit.
Can I keep driving?
Limit driving and address an active DEF or NOx warning promptly, especially if a no-start countdown appears. A false high temperature can interfere with reductant dosing or tank-heating control and may lead to an emissions failure or a vehicle that will not restart.
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.