Main Relay

This procedure covers the removal and replacement of the main relay (also known as the power relay or EMS main relay) in the engine compartment fuse box of a 2015 Kia Forte with the 1.8L I4 engine.

Warnings

Tools required

Parts

• Main relay (EMS power relay) × 1 — Use OEM specification

Preparation

1. Ensure the ignition is in the OFF position and the key is removed
2. Open the hood and secure it in the raised position
3. Locate the engine compartment fuse box on the driver's side near the battery
4. Disconnect the negative battery terminal to prevent electrical shorts

Procedure

1. 1

   Disconnect the negative battery terminal
   Using a 10mm socket, loosen the negative battery terminal bolt. Remove the negative cable from the battery post and secure it away from the battery to prevent accidental contact.
   Torque spec

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

   Remove the engine compartment fuse box cover
   Release the clips or tabs securing the fuse box cover by pressing or pulling as designed. Lift the cover away to expose the relays and fuses inside. On some models, there may be two covers (upper and lower) - remove the upper cover first.
3. 3

   Locate the main relay
   Identify the main relay (also labeled as EMS or ECM relay) using the diagram on the underside of the fuse box cover or in the owner's manual. It is typically a larger relay, often in a prominent position within the fuse box. Verify the relay position matches the symptom (no-start or intermittent power loss).
4. 4

   Remove the main relay
   Firmly grasp the main relay body and pull straight upward with steady pressure to release it from its socket. If the relay is difficult to remove, use a relay puller tool or carefully use needle-nose pliers to grip the relay body (not the terminals). Rock the relay gently side-to-side while pulling if needed. Inspect the relay socket terminals for corrosion, burning, or damage.
   ⚠Do not pull on the relay wiring harness. Pull only on the relay body itself to avoid damaging the socket terminals.
5. 5

   Inspect the relay socket and terminals
   Examine the socket where the relay was installed. Look for signs of overheating (melted plastic, discoloration), corrosion (green or white deposits), or bent/damaged terminals. If corrosion is present, clean with electrical contact cleaner. If the socket is damaged or melted, the entire fuse box may require replacement.
6. 6

   Install the new main relay
   Align the new main relay with the socket, ensuring the relay terminals match the socket configuration. There is typically a notch or asymmetric design to prevent incorrect installation. Press the relay firmly into the socket until it is fully seated and flush with the surrounding relays. Verify the relay cannot be pulled out with light finger pressure.
7. 7

   Reinstall the fuse box cover
   Position the fuse box cover over the fuse box, aligning any guide tabs or clips. Press down firmly until all clips engage and the cover is secure. Ensure the cover is fully seated to prevent moisture intrusion.
8. 8

   Reconnect the battery negative terminal
   Clean the battery post and cable terminal if necessary. Place the negative cable onto the negative battery post and tighten the terminal bolt using a 10mm socket and torque wrench to specification.
   ⚠Do not overtighten the battery terminal bolt as this can damage the terminal clamp or battery post.
   Torque spec

   Battery Terminal Bolts6 Nm (4 lb-ft)

Reassembly

1. Ensure all fuse box covers are properly secured and all clips are engaged
2. Verify the battery terminal connection is tight and corrosion-free
3. Close the hood after verification is complete

Verification

• Turn the ignition to the ON position (without starting) and verify the check engine light illuminates briefly then extinguishes, indicating the ECM has power
• Start the engine and verify it cranks and starts normally without hesitation
• Allow the engine to idle for 5-10 minutes to relearn idle parameters and verify no warning lights appear on the dash
• Turn the engine off and restart to confirm the relay is functioning properly under multiple start cycles
• Check for any diagnostic trouble codes using an OBD-II scanner if warning lights appear

Related trouble codes on this vehicle

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