Cooling Fan Relay

This procedure covers the diagnosis and replacement of the cooling fan relay in a 2007 Ram 3500 with the 5.9L Cummins diesel engine.

Warnings

Tools required

Parts

• Cooling fan relay × 1 — Use OEM specification
• Dielectric grease × 1 — Optional for relay terminals

Preparation

1. Park vehicle on level surface and engage parking brake
2. Turn ignition to OFF position and remove key
3. Allow engine to cool to ambient temperature if recently operated
4. Disconnect negative battery cable and wait 2 minutes for system discharge

Procedure

1. 1

   Locate the Power Distribution Center
   Open the hood and locate the Power Distribution Center (PDC) on the driver side of the engine compartment, near the battery. This is a black rectangular box containing fuses and relays.
2. 2

   Access the relay cavity
   Remove the PDC cover by pressing the release tabs on either side and lifting upward. Refer to the relay diagram on the underside of the cover to identify the cooling fan relay location. On 2007 Ram 3500 models, the fan relay is typically in the front row of relays.
3. 3

   Test the existing relay (optional)
   If you have a multimeter, test the relay before removal. Check for continuity between terminals 85 and 86 (coil circuit) and resistance should be 60-120 ohms. Check terminals 30 and 87 with power applied to the coil; they should show continuity when energized. This confirms whether the relay is actually faulty.
4. 4

   Remove the cooling fan relay
   Grasp the relay firmly and pull straight upward to remove it from the socket. The relay should release with moderate force. If stuck, gently rock it side-to-side while pulling upward. Do not pry against the PDC housing as this can damage the mounting posts.
5. 5

   Inspect the relay socket
   Examine the relay socket terminals for corrosion, burning, or damage. Clean any corrosion with electrical contact cleaner and a small wire brush. Check for pushed-back or bent terminals that may prevent proper contact. Inspect the socket for melted plastic indicating overheating from a short circuit or excessive current draw.
6. 6

   Verify relay specification
   Compare the old relay to the new relay to ensure correct specifications. The relay is typically an ISO mini relay rated around 30-40 amps and may be a 4-terminal (85, 86, 30, 87) or 5-terminal (85, 86, 30, 87, 87a) configuration. Compare the new relay to the old one and verify the terminal count and configuration match exactly before installation.
7. 7

   Install the new relay
   Apply a small amount of dielectric grease to the relay terminals if desired for corrosion protection. Align the relay with the socket ensuring proper terminal orientation. Push the relay firmly into the socket until it seats completely and is flush with surrounding relays. The relay should click into place.
8. 8

   Reinstall the PDC cover
   Position the PDC cover over the fuse and relay box, ensuring all tabs align properly. Press down firmly until all latches engage and the cover is secure. Verify the cover is seated properly on all sides.
9. 9

   Reconnect the battery
   Reconnect the negative battery cable to the battery terminal. Tighten the battery cable clamp securely to ensure good electrical contact.

Reassembly

1. Ensure the PDC cover is properly secured to prevent water and debris entry
2. Verify all tools and parts have been removed from the engine compartment

Verification

• Start the engine and allow it to reach operating temperature while monitoring coolant temperature gauge
• The cooling fan should engage automatically when coolant temperature reaches approximately 220-230°F
• Listen for the fan motor engaging; you should hear the fan running and feel strong airflow through the radiator
• If equipped with air conditioning, turn on the AC at maximum setting; the cooling fan should engage immediately
• Turn off the engine and verify the fan stops running (some delayed operation is normal on diesel engines)
• Check for any error codes using a scan tool if the fan does not operate as expected
• If fan still does not operate, further diagnosis of the fan motor, temperature sensor, or wiring harness may be required

Related trouble codes on this vehicle

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