P2045
Reductant Temperature Sensor A Circuit High
Diesel exhaust / SCR (DEF)
Generic OBD-II
Medium
What it means
P2045 means the signal from the reductant (diesel exhaust fluid / DEF) temperature sensor A is too high — usually an open or a short to voltage in the circuit, or a failed sensor. The SCR system uses this reading to dose DEF correctly and reduce NOx, so a fault can disable emissions control and, on many diesels, trigger a power-derate countdown.
Medium
Can I keep driving? Drivable in the short term, but many diesels start an emissions derate countdown that progressively limits power until the SCR fault is fixed.
Common symptoms
What you'll notice
- Check-engine light on
- SCR / DEF or emissions-system warning message
- Possible reduced power or an emissions derate countdown
Common causes
Most likely first
- Faulty reductant (DEF) temperature sensorLikely
- Open or short-to-voltage in the sensor wiringCommon
- Corroded or loose connector at the sensorCommon
- Failed PCM / reductant control module (rare)Less often
How to diagnose & fix
Work through it in order
- Scan freeze-frame and note any companion SCR/DEF codes.
- Inspect the sensor's connector and wiring for opens or shorts to voltage.
- Measure the sensor's resistance/signal against spec.
- Replace the reductant temperature sensor if it's out of range.
- Clear the code and complete a drive cycle to confirm the SCR monitor.
FAQ
Quick answers
Is it safe to drive with P2045?+
For a short time, yes, but the DEF/SCR system may not dose correctly, and many diesels begin a power-derate countdown. Get it fixed before the derate limits the vehicle.
Can I just clear P2045?+
It returns until the sensor or wiring is repaired, since the module keeps seeing a high signal. Fix the circuit first.
Related codes
Often seen with P2045
Read & clear P2045 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX