Reductant Temperature Sensor Circuit
The P2042 code means the vehicle's onboard diagnostic system has detected: Reductant Temperature Sensor Circuit. This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- moderate
- Estimated cost
- $150 - $500 (parts and labor)
Best-selling code reader on Amazon. Reads and clears check engine codes on any 1996+ vehicle. Under $30.
Essential for diagnosing sensor codes, checking voltage, and testing circuits. Under $15 and pays for itself on the first job.
Affiliate links — we earn a commission at no extra cost to you.
Common Symptoms
- Check Engine Light on
- DEF system warning light
- Possible reduced engine power
- SCR system may not function optimally
- DEF quality may not be properly monitored
Probable Causes (Ranked by Likelihood)
- Faulty reductant (DEF) temperature sensor Very High
- Corroded sensor connector in DEF tank High
- Wiring fault between DEF tank and PCM Moderate
- DEF tank contamination affecting sensor Moderate
- PCM circuit fault Low
Frequently Asked Questions
What does P2042 mean?
P2042 indicates a malfunction in the reductant (DEF) temperature sensor circuit, which monitors the temperature of the diesel exhaust fluid to ensure proper injection rates.
Can I drive with a P2042 code?
You can drive short distances, but the SCR system may not function optimally, which could trigger a speed limiter countdown on some vehicles.
How much does it cost to fix P2042?
Repair costs are typically $150 to $500, with the sensor often being part of the DEF tank sender assembly.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
-
Confirm P2042 with scan tool and freeze frame data
-
Check DEF temperature sensor connector at the tank for corrosion
-
Measure sensor resistance at known temperature
-
Inspect wiring harness between DEF tank and PCM
Sources 2
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
Commonly Affected Vehicles
- 2010-2016 Mercedes-Benz ML350 3.0L BlueTEC
- 2014-2020 Ram 3500 6.7L Cummins
- 2011-2017 Ford F-350 6.7L Power Stroke
- 2012-2019 Chevrolet Silverado 3500 6.6L Duramax
Related Codes
Explore More
Was this helpful?
Send this to whoever is fixing the car — your mechanic, or the person asking what the light means.