This procedure covers the replacement of the main power relay in a 2024 Rivian EDV 500, which controls primary high-voltage power distribution to the electric drive system.

Warnings

Tools required

Parts

• Main power relay assembly × 1 — Use OEM specification
• High-voltage connector seal × 1 — Use OEM specification

Preparation

1. Park vehicle on level surface and apply parking brake
2. Ensure vehicle has been powered off for at least 15 minutes before beginning work
3. Verify you have high-voltage safety certification and appropriate PPE
4. Connect Rivian diagnostic scanner and document any existing fault codes
5. Ensure fire extinguisher rated for electrical fires is readily accessible
6. Place high-voltage service warning tags on steering wheel and charge port

Procedure

1. 1

   Disconnect 12V battery
   Open the front trunk (frunk). Locate the 12V battery in the driver's side compartment. Using a 10mm socket, disconnect the negative terminal first, then the positive terminal. Secure cables away from battery posts using cable ties or tape to prevent accidental reconnection.
2. 2

   Access HV disconnect location
   Remove the rear cargo area floor panels by releasing the four quarter-turn fasteners. Fold back the floor covering to expose the HV battery access panel. Remove eight T25 Torx screws securing the HV access panel and carefully lift panel away.
3. 3

   Perform high-voltage isolation
   Locate the orange manual service disconnect (MSD) plug at the front of the battery pack. Rotate the MSD lock counterclockwise 90 degrees, then pull straight up to remove the service disconnect plug. Insert the service wedge into the MSD receptacle to prevent reinstallation. This mechanically isolates the high-voltage system.
   ⚠️Wait minimum 5 minutes after removing MSD before proceeding. High-voltage capacitors must fully discharge.
4. 4

   Verify zero voltage
   Using a calibrated high-voltage multimeter, verify zero voltage across the HV bus bars at the MSD location. Measure DC voltage between positive and negative terminals, then from each terminal to vehicle ground. All readings must be below 2V DC before proceeding. Document voltage readings.
5. 5

   Remove underbody shield
   From underneath the vehicle, locate the motor control unit (MCU) underbody shield. Remove twelve 8mm bolts securing the shield and lower it carefully. The main relay assembly is mounted on the MCU housing.
6. 6

   Access main relay assembly
   The main relay is located on the driver's side of the MCU housing. Remove the relay cover by pressing the two side release tabs and pulling straight out. You should now see the main relay with multiple orange HV connectors and smaller low-voltage control connectors.
7. 7

   Disconnect low-voltage control connectors
   Locate the two low-voltage connectors on the relay assembly (typically gray and black 12-pin connectors). Press the connector lock tabs and carefully pull each connector straight off. Note orientation and position for reinstallation.
8. 8

   Remove high-voltage connections
   Wearing high-voltage insulated gloves, depress the orange safety lock on each HV connector. Slide the lock collar back on each connector, then carefully pull the connector straight off the relay terminal. There are typically two large HV input connectors and two HV output connectors. Support connector weight to avoid damage.
   ⚠HV connectors are keyed and can only be installed one way. Take photos before removal to document correct orientation.
9. 9

   Remove main relay mounting
   Remove the four 10mm bolts securing the main relay assembly to the MCU housing. Support the relay assembly as you remove the final bolt, as it weighs approximately 8-10 lbs. Carefully lift the relay assembly straight up and away from the MCU, being mindful of any remaining brackets or clips.
10. 10

    Install new main relay assembly
    Position the new main relay assembly onto the MCU housing, aligning the mounting holes and ensuring proper orientation. Install the four 10mm mounting bolts and tighten in a cross pattern. Verify relay sits flush against mounting surface with no gaps.
11. 11

    Reconnect high-voltage connections
    Wearing high-voltage insulated gloves, align each HV connector with its corresponding terminal on the new relay. Push each connector straight on until it clicks into place. Slide the orange safety lock collar forward over the connection point and verify it locks. Apply thin coat of dielectric grease to seal surfaces if specified by service manual.
    ⚠Ensure connectors are fully seated with audible click. Partially seated HV connectors can cause arcing and component failure.
12. 12

    Reconnect low-voltage control connectors
    Align and push each low-voltage control connector onto the relay assembly until the lock tab clicks. Verify both connectors are fully seated by attempting to gently pull them off - they should not release without pressing the lock tab.
13. 13

    Reinstall relay cover and underbody shield
    Snap the relay protective cover back into place over the relay assembly. From underneath vehicle, position the MCU underbody shield and install all twelve 8mm bolts. Tighten bolts evenly to ensure proper shield seating.
14. 14

    Restore high-voltage system
    Remove the service wedge from the MSD receptacle. Align the MSD plug with the receptacle, ensuring the key is properly oriented. Push the plug straight down until fully seated, then rotate the lock clockwise 90 degrees until it clicks. The lock must be in the vertical locked position.
15. 15

    Complete system restoration
    Reinstall the HV access panel using the eight T25 Torx screws. Replace the rear cargo floor panels and secure quarter-turn fasteners. Reconnect the 12V battery positive terminal first, then negative terminal, both using 10mm socket. Remove all high-voltage warning tags from vehicle.

Reassembly

1. Verify all HV connectors are fully seated with safety locks engaged
2. Ensure all underbody panels and shields are properly secured
3. Confirm MSD plug is locked in place with indicator in locked position
4. Double-check all tools and service equipment are removed from vehicle

Verification

• Connect diagnostic scanner and power on vehicle - verify no new fault codes related to main relay or HV system
• Using diagnostic tool, perform main relay functional test to verify proper operation
• Check for any warning lights on instrument cluster - resolve before returning to service
• Perform stationary pre-drive check: verify ready light illuminates and no HV system warnings present
• Conduct test drive to verify normal operation under various load conditions
• Re-scan for fault codes after test drive and verify all systems operational
• Document repair in vehicle service history with relay part number and any calibration performed

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