Coolant Temperature Sensor

Replace the coolant temperature sensor on the 5.9L Cummins diesel engine to restore accurate temperature readings to the ECM and gauge cluster.

Warnings

Tools required

Parts

• Coolant temperature sensor × 1 — Use OEM specification
• Coolant (if topping off) × 1 — Ethylene glycol 50/50 mix

Fluids

• coolant — 1 qt

Preparation

1. Park vehicle on level surface and allow engine to cool completely (minimum 2 hours)
2. Disconnect negative battery cable to prevent false trouble codes
3. Locate the coolant temperature sensor on the driver's side of the thermostat housing near the front of the engine
4. Place drain pan under the work area to catch coolant spillage

Procedure

1. 1

   Relieve cooling system pressure
   Slowly loosen the radiator cap to release any residual pressure in the cooling system. Remove the cap completely once pressure is fully released.
2. 2

   Disconnect sensor electrical connector
   Press the tab on the coolant temperature sensor electrical connector and pull straight back to disconnect. Do not pull on the wires themselves.
3. 3

   Remove coolant temperature sensor
   Using the correct size socket (verify sensor hex size, commonly 19mm) and ratchet, carefully unthread the coolant temperature sensor from the thermostat housing. Expect coolant to drain from the opening once the sensor is removed. Allow coolant to drain into the pan below.
4. 4

   Clean sensor mounting location
   Use a small wire brush to clean the threads in the thermostat housing. Remove any old thread sealant, corrosion, or debris. Wipe the area clean with a shop towel.
5. 5

   Install new coolant temperature sensor
   Thread the new coolant temperature sensor into the thermostat housing by hand until it seats. Ensure it threads smoothly without cross-threading. Tighten the sensor to firm contact using the correct size socket. Do not over-torque as the sensor requires only light torque (verify against OEM spec, commonly around 11-14 lb-ft) to avoid stripping the aluminum threads.
   ⚠The sensor should be snug but not excessively tight. Over-torquing will strip the aluminum housing threads.
6. 6

   Reconnect electrical connector
   Push the electrical connector firmly onto the new coolant temperature sensor until it clicks into place. Verify the locking tab is fully engaged.
7. 7

   Refill and bleed cooling system
   Add coolant to the radiator to bring level back to the cold fill line. Start the engine and allow it to reach operating temperature with the radiator cap off. Add coolant as needed as air purges from the system. Once the thermostat opens and coolant circulates, top off the radiator and install the cap. This engine has no separate bleed screw; air is purged by running with the cap off.
   Torque spec

   Bleed Screw7 Nm (5 lb-ft)
8. 8

   Reconnect battery
   Reconnect the negative battery cable. Ensure the terminal is clean and tight.

Reassembly

1. Verify all electrical connections are secure and properly seated
2. Check for coolant leaks around the sensor after the engine reaches operating temperature
3. Top off coolant overflow reservoir to the appropriate level

Verification

• Start the engine and monitor the temperature gauge to confirm it reads normal operating temperature (approximately 180-200°F)
• Use a scan tool to verify the ECM is receiving accurate coolant temperature readings (should match actual engine temperature within 5-10 degrees)
• Inspect the sensor area for any coolant leaks after a test drive
• Clear any diagnostic trouble codes that may have been set by the faulty sensor

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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