P2042 — Reductant Temperature Sensor Circuit

OBD2 code P2042 flags a problem with the sensor and actuator circuits (reductant temperature sensor circuit). The car is usually drivable while you plan the repair. Common culprits: blown fuse feeding the circuit, corroded, loose or damaged connector, poor ground connection.

powertrain (engine/transmission)

Is it safe to drive?

Short-term driving is OK In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm P2042 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the reductant temperature sensor circuit for damage, corrosion, chafing or poor contact.
Subsystem check Measure reference voltage, ground and signal continuity at the component connector.
Subsystem check Wiggle-test the harness while watching the signal in live data — dropouts reveal broken wires.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P2042 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P2042 (parts and labor, USD, independent shop rates): Control module repair: $300–$1,000; Repair wiring or connectors: $80–$250; Replace the faulty sensor or actuator: $150–$500. Overall, fixing P2042 usually costs between $80 and $1,000. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

What does OBD2 code P2042 mean?

What is the most common cause of P2042?

The most common causes are: blown fuse feeding the circuit, corroded, loose or damaged connector, poor ground connection.

Will P2042 clear itself?

Sometimes P2042 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

How do I diagnose P2042 myself?

Start with a scan: confirm P2042, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the sensor and actuator circuits, and verify the suspect component against live data before buying parts.

Is it safe to drive with P2042?

In most cases the car remains drivable, possibly with reduced performance or a disabled auxiliary system. If symptoms include stalling, no-start or brake/steering warnings, treat it as urgent.

What does P2042 mean?

When P2042 appears on a scan, it means the control module has flagged a problem in the sensor and actuator circuits: reductant temperature sensor circuit. The fault sits in the powertrain (engine/transmission) group of the OBD2 standard.

This code does not appear from a single bad reading: the module must see the fault condition repeat under defined operating conditions before it turns on the warning light. The freeze frame captured with P2042 — engine load, rpm, temperature, speed — tells you exactly when the problem occurs, so reproduce those conditions when testing.

What causes P2042?

corroded, loose or damaged connector
faulty sensor or actuator of the affected circuit
poor ground connection
blown fuse feeding the circuit

Common symptoms of P2042

increased fuel consumption in some cases
the affected system operates intermittently or not at all
Check Engine Light on
possible limp mode depending on the affected component

How to diagnose P2042

Connect an OBD2 scanner, confirm P2042 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Visually inspect the wiring harness and connectors related to the reductant temperature sensor circuit for damage, corrosion, chafing or poor contact.
Measure reference voltage, ground and signal continuity at the component connector.
Wiggle-test the harness while watching the signal in live data — dropouts reveal broken wires.
Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P2042 does not return.

How to fix P2042

Start with the cheapest and most common causes before replacing expensive parts:

Control module repair — $300–$1,000
Repair wiring or connectors — $80–$250
Replace the faulty sensor or actuator — $150–$500

How much does it cost to fix P2042?

Repair cost depends on which component actually failed. Typical scenarios for P2042 (parts and labor, USD, independent shop rates):

Control module repair: $300–$1,000
Repair wiring or connectors: $80–$250
Replace the faulty sensor or actuator: $150–$500

Overall, fixing P2042 usually costs between $80 and $1,000. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Can you drive with P2042?