P2042

Reductant Temperature Sensor A Circuit

Q: Is it safe to drive with P2042?

Short-term yes, but the DEF/SCR system can force reduced power if emissions faults go unresolved, so don't put the repair off.

Q: Can I just clear P2042?

It returns until the sensor or wiring is fixed, and clearing it won't stop an emissions derate countdown.

Auxiliary emissions control Generic OBD-II Medium

What it means

P2042 means the engine computer sees a circuit fault at reductant temperature sensor A, part of the diesel SCR/DEF (exhaust-fluid) emissions system. This sensor monitors DEF temperature so the system can dose correctly and avoid freezing. The engine runs normally at first, but unresolved emissions faults can trigger a power derate, so it's worth fixing promptly.

Medium

Can I keep driving? Yes for now — but this is part of the diesel emissions (SCR/DEF) system, and an unfixed fault can lead to a power derate; repair soon.

Real-world scan data

Seen in

scans in the past year

Found in

<0.1%

of scans

<0.1%

of scans that found faults

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

Common symptoms

What you'll notice

Check-engine light on
SCR/emissions warning message and possible countdown to reduced power
Usually no change in how the engine runs at first

Common causes

Most likely first

Faulty reductant (DEF) temperature sensor ALikely
Open or short in the reductant temperature sensor wiringCommon
Corroded or loose connector at the sensorCommon
Failed powertrain control module (PCM)Less often

How to diagnose & fix

Work through it in order

Read freeze-frame data and inspect the reductant temperature sensor connector and wiring for damage or corrosion.
Check the sensor circuit for opens or shorts against the wiring diagram; repair as needed.
Compare the sensor's resistance/reading to spec; replace the reductant temperature sensor if out of range.
Clear the code and confirm the reading is plausible after a drive cycle.

FAQ

Quick answers

Is it safe to drive with P2042?+

Short-term yes, but the DEF/SCR system can force reduced power if emissions faults go unresolved, so don't put the repair off.

Can I just clear P2042?+

It returns until the sensor or wiring is fixed, and clearing it won't stop an emissions derate countdown.

Read & clear P2042 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX