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P2042 — Reductant Temperature Sensor Circuit

Manufacturer-specificPowertrain (engine & transmission)

Code P2042 indicates a malfunction in the electrical circuit for the reductant (Diesel Exhaust Fluid) temperature sensor, which monitors DEF temperature to protect the selective catalytic reduction system. The powertrain control module has detected a signal that is outside the expected range, intermittent, or otherwise implausible. This typically results from a sensor failure, wiring problem, or connection issue within the reductant temperature sensor circuit.

Symptoms

What causes it — most likely first

1. Faulty reductant temperature sensor

The sensor itself is the most common failure point, as internal drift, cracking, or seal failure can produce an out-of-range or erratic signal that the module interprets as a circuit fault.

2. Wiring or connector fault in the sensor circuit

Opens, shorts-to-ground, shorts-to-voltage, or chafed wires between the sensor and the control module can interrupt or distort the temperature signal.

3. DEF crystallization or contamination at the sensor

Dried Diesel Exhaust Fluid can crystallize on the sensor probe or inside the connector, creating resistance paths or physical damage that affects the circuit integrity.

4. Corroded or loose electrical terminals

Moisture intrusion at the sensor or harness connector can corrode pins or create high-resistance connections, causing intermittent or implausible circuit readings.

5. Control module (PCM) malfunction

An internal PCM fault affecting the specific input circuit is possible but statistically rare; it should only be considered after the sensor and wiring have been thoroughly tested and ruled out.

How it's diagnosed

  1. Visually inspect the reductant temperature sensor and its connector for crystallization, corrosion, bent pins, or physical damage.
  2. Test the sensor using a digital multimeter or scan-tool data, comparing its resistance or voltage output to manufacturer specifications for the current fluid temperature.
  3. Perform continuity, short-to-ground, and short-to-voltage tests on the entire wiring harness between the sensor and the control module connector.
  4. Compare live reductant temperature data against ambient air and engine coolant temperatures to confirm whether the sensor reading is plausible.
  5. Verify control module software is up to date and retest; evaluate the PCM only if the sensor and all wiring test perfectly normal and the fault remains.

Code facts & related codes

SystemPowertrain (engine & transmission)
StandardizationManufacturer-specific (P1/B1/C1/U1)
Related codesP2040 — Reductant Injection Air Pressure SensoP2041 — Reductant Injection Air Pressure SensoP2043 — Reductant Temperature Sensor Circuit RP2044 — Reductant Temperature Sensor Circuit LP2045 — Reductant Temperature Sensor Circuit HP2046 — Reductant Temperature Sensor Circuit I

Frequently asked

Is P2042 an emergency?

It is not immediately dangerous, but affected vehicles may enter a reduced-power derate or start-prevention sequence if the fault persists, so prompt diagnosis is recommended.

Can I continue driving with this code?

Short trips are usually possible, but prolonged operation may trigger progressive power reductions and will likely cause an emissions-inspection failure.

Will I need to replace my PCM?

Almost never. The sensor, wiring, or connector is the actual cause in the vast majority of cases. PCM replacement is an extremely rare last-resort diagnosis after the entire circuit has been verified good.

Can contaminated DEF fluid cause this code?

Crystallized or incorrect fluid can coat or damage the sensor and contribute to circuit faults, but the code specifically indicates an electrical circuit issue rather than fluid quality alone.