This procedure covers the replacement of the main relay in a 2016-2024 Hyundai Tucson with a 2.5L I4 AWD engine, located in the engine compartment fuse/relay box.

Warnings

Tools required

Parts

• Main relay (fuel pump relay) × 1 — Use OEM specification - verify relay number from fuse box diagram

Preparation

1. Park vehicle on level ground and engage parking brake
2. Turn ignition to OFF position and remove key
3. Allow engine to cool completely if recently operated
4. Open hood and secure with prop rod
5. Locate the engine compartment fuse/relay box on the driver's side near the battery
6. Have replacement relay verified against fuse box diagram on underside of fuse box cover

Procedure

1. 1

   Disconnect battery negative terminal
   Using a 10mm socket, loosen the negative battery terminal clamp bolt. Remove the negative cable from the battery post and secure it away from the battery to prevent accidental contact. Wait at least 3 minutes for electrical systems to discharge.
   Torque spec

   Battery Terminal Bolts6 Nm (4 lb-ft)
2. 2

   Access the fuse/relay box
   Locate the engine compartment fuse/relay box on the driver's side of the engine bay. Release the retaining clips on both sides of the fuse box cover by pressing or pulling them outward, then lift the cover off carefully to expose the relays and fuses.
3. 3

   Identify the main relay location
   Reference the fuse/relay diagram printed on the underside of the fuse box cover or in the owner's manual to locate the main relay (also called fuel pump relay or EFI relay). It is typically a larger relay in the main relay section, often labeled as 'MAIN' or 'EFI'. Note the relay orientation and pin configuration before removal.
4. 4

   Remove the faulty main relay
   Using a relay puller tool or needle-nose pliers, firmly grip the main relay body and pull straight upward with steady pressure to remove it from the socket. Avoid rocking or twisting which could damage the socket terminals. Inspect the relay socket terminals for corrosion, burning, or damage.
   ⚠Do not use excessive force or pry tools that could damage socket terminals or surrounding components
5. 5

   Inspect and clean relay socket
   Examine the relay socket terminals for any signs of heat damage, corrosion, or bent pins. If corrosion is present, spray electrical contact cleaner into the socket and allow to dry completely. If terminals are damaged or melted, the entire fuse box may require replacement - consult a professional.
6. 6

   Install new main relay
   Verify the new relay matches the original in size, pin configuration, and part number. Align the relay pins with the socket, ensuring proper orientation (there is typically a notch or tab for alignment). Press the relay firmly and evenly into the socket until it is fully seated and flush with surrounding relays.
   ⚠Ensure relay is oriented correctly before pressing into socket to avoid bending pins
7. 7

   Reinstall fuse box cover
   Position the fuse box cover back onto the fuse/relay box, ensuring it seats properly. Press down on the cover edges until the retaining clips engage with an audible click on both sides. Verify the cover is secure and sealed against moisture intrusion.
8. 8

   Reconnect battery negative terminal
   Clean the battery negative terminal and post with a wire brush if corrosion is present. Place the negative cable back onto the negative battery post and tighten the clamp bolt to the specified torque. Ensure the connection is secure and the cable cannot rotate on the post.
   ⚠Do not overtighten battery terminal bolts as this can crack the terminal or damage the battery post
   Torque spec

   Battery Terminal Bolts6 Nm (4 lb-ft)

Reassembly

1. Ensure fuse box cover is properly secured with all clips engaged
2. Verify no tools or parts are left in the engine compartment
3. Reset clock and radio presets as needed

Verification

• Turn ignition to ON position (do not start) - listen for fuel pump prime (2-3 second hum from rear of vehicle)
• Check that all dashboard warning lights perform normal self-test cycle
• Start the engine and verify it starts normally without extended cranking
• Allow engine to idle and confirm stable operation with no warning lights
• Turn off engine and restart to confirm relay functions consistently
• Verify all electrical accessories (lights, radio, windows) operate normally
• If available, use a scan tool to check for any stored diagnostic trouble codes related to fuel system or main relay

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