Cooling Fan Relay

This procedure covers the replacement of the cooling fan relay in the 2016-2021 Honda Civic 1.5L Turbo, located in the under-hood fuse/relay box.

Warnings

Tools required

Parts

• Cooling fan relay (MITSUBA type, 4-pin 30A) × 1 — Honda 39794-SDA-A03 or equivalent

Preparation

1. Park vehicle on level surface and turn off ignition
2. Allow engine to cool completely if recently operated
3. Locate the under-hood fuse/relay box on driver's side of engine bay, near the firewall
4. Identify cooling fan relay position using diagram on underside of fuse box cover

Procedure

1. 1

   Open fuse/relay box cover
   Release the clips securing the under-hood fuse/relay box cover by pressing the tabs on each side. Lift the cover upward and set aside. Note the relay diagram printed on the underside of the cover showing relay positions.
2. 2

   Identify cooling fan relay
   Locate the cooling fan relay in the fuse/relay box. On 2016-2021 Civic 1.5L Turbo models, the cooling fan relay is typically labeled as 'RADIATOR FAN' or similar designation. It is a 4-pin 30A relay, usually positioned in the second or third row of relays. Verify position matches the diagram on the fuse box cover.
3. 3

   Test existing relay (optional)
   If diagnosing a cooling fan issue, use a multimeter to test relay continuity before removal. Check for 12V at the relay socket terminals with ignition on and engine at operating temperature. This confirms the issue is the relay and not wiring or fan motor.
4. 4

   Remove old cooling fan relay
   Grip the relay body firmly and pull straight upward with steady pressure to extract it from the socket. The relay is held by friction fit terminals only. If the relay is difficult to remove, gently rock it side-to-side while pulling upward. Do not use excessive force that could damage the socket.
5. 5

   Inspect relay socket
   Examine the relay socket terminals for corrosion, damage, or signs of overheating (discoloration or melted plastic). If terminals are corroded, clean gently with electrical contact cleaner and a small brush. If socket shows heat damage, the entire fuse/relay box may require replacement.
6. 6

   Install new cooling fan relay
   Align the new relay pins with the socket terminals, ensuring proper orientation by matching the relay pin configuration with the socket layout. Press the relay firmly into the socket until it is fully seated and flush with surrounding relays. The relay should click into place when properly installed.
7. 7

   Reinstall fuse box cover
   Position the fuse/relay box cover over the box and press down until all clips engage securely. Ensure the cover is fully seated and latched on all sides.

Reassembly

1. Ensure fuse box cover is properly secured with all clips engaged
2. Verify no tools or parts were left in engine bay

Verification

• Start the engine and allow it to reach operating temperature (approximately 200°F / 93°C) with AC off
• Verify the cooling fan activates when engine temperature reaches threshold
• Test cooling fan operation with AC on at idle - fan should activate immediately
• Listen for proper relay clicking sound when fan engages and disengages
• Check for any warning lights on instrument cluster related to cooling system
• If fan still does not operate, verify fan motor and wiring harness are functioning properly

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