Coolant Temperature Sensor

This procedure covers removal and replacement of the engine coolant temperature sensor on the 5.9L Cummins diesel engine.

Warnings

Tools required

Parts

• Engine coolant temperature sensor × 1 — Use OEM specification
• Coolant temperature sensor O-ring or seal × 1 — Usually included with sensor

Fluids

• HOAT coolant 50/50 — 1 qt

Preparation

1. Ensure engine is completely cold to the touch
2. Park vehicle on level surface and engage parking brake
3. Open hood and secure with prop rod
4. Disconnect negative battery cable to prevent fault codes during sensor disconnection
5. Locate coolant temperature sensor on driver side of engine block, below fuel filter assembly near thermostat housing

Procedure

1. 1

   Access the coolant temperature sensor
   Identify the coolant temperature sensor located in the thermostat housing at the front of the engine. Verify exact location against the specific engine before proceeding. The sensor has a single-pin electrical connector and threads into the thermostat housing on the front of the engine. Clear any obstructions or hoses that may interfere with access.
2. 2

   Disconnect electrical connector
   Press the locking tab on the electrical connector and pull straight away from the sensor. Do not pull on the wires themselves. Inspect the connector terminals for corrosion or damage. If connector is corroded, clean with electrical contact cleaner.
3. 3

   Position drain pan
   Place a drain pan directly beneath the coolant temperature sensor. While coolant loss should be minimal, residual coolant in the passages will drain when the sensor is removed. Have shop towels ready to catch any spillage.
4. 4

   Remove coolant temperature sensor
   Using the correct size deep socket (verify size, commonly 19mm) and ratchet, loosen the coolant temperature sensor by turning counterclockwise. Once loose, quickly unthread the sensor by hand to minimize coolant loss. Remove the sensor completely and allow residual coolant to drain into the pan. Inspect the sensor threads and sealing surface for damage or debris.
5. 5

   Clean sensor bore
   Use a wire brush or clean shop towel to clean the sensor mounting threads in the engine block or thermostat housing. Remove any old sealant, corrosion, or debris. Ensure the sealing surface is clean and undamaged. Inspect threads for damage or cross-threading.
6. 6

   Prepare new sensor
   Remove the new coolant temperature sensor from packaging. Verify it matches the old sensor in thread size, length, and connector type. Check that the O-ring or seal is properly seated on the new sensor. Do not apply additional thread sealant unless specified by the manufacturer, as the sensor typically uses an integral seal.
7. 7

   Install new sensor
   Thread the new coolant temperature sensor into the mounting bore by hand, turning clockwise. Ensure it threads smoothly without resistance. Once hand-tight, use the correct size deep socket (verify size, commonly 19mm) to snug the sensor. Tighten firmly but do not overtighten, as this can damage the sensor body or threads. Tighten to the factory specification, approximately 11-13 ft-lbs (about 15 Nm). Do not overtighten as this can damage the sensor body or threads. Verify the torque spec for this component before final tightening.
8. 8

   Reconnect electrical connector
   Push the electrical connector firmly onto the new sensor until the locking tab clicks into place. Verify the connection is secure by gently tugging on the connector body. Ensure the wiring is routed away from hot exhaust components and moving parts.
9. 9

   Check coolant level
   Open the radiator cap or coolant reservoir cap and check coolant level. Add the manufacturer-specified coolant (verify type; factory fill is typically HOAT 50/50) as needed to bring level to the proper mark. The system should require minimal top-off if the procedure was performed quickly. Do not overfill.
10. 10

    Reconnect battery and clear codes
    Reconnect the negative battery cable. If a scan tool is available, clear any diagnostic trouble codes that may have been set during the repair. If no scan tool is available, codes should clear after several successful drive cycles.

Reassembly

1. Ensure all electrical connections are secure and properly locked
2. Verify coolant level is correct and radiator cap is properly installed
3. Inspect work area for tools or parts left behind
4. Wipe up any spilled coolant from engine surfaces

Verification

• Start the engine and allow it to reach normal operating temperature while monitoring for coolant leaks around the sensor
• Observe the temperature gauge to verify it rises normally and stabilizes in the normal range
• Use a scan tool to verify the coolant temperature sensor is reading accurately and matches actual engine temperature
• Check for diagnostic trouble codes related to coolant temperature sensor circuit or performance
• After test drive, recheck coolant level and top off if necessary
• Verify no coolant leaks are present around the sensor after reaching full operating temperature

Related trouble codes on this vehicle

Codes that commonly send this job to the bay — tap one for symptoms, causes, and diagnostic steps.

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