Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Main Relay: Notes
The Main Relay provides power for the EMS2000 and other system components. It has an additional function of protecting system components from reverse battery polarity. (Main Relay will not energize with reverse polarity.)
When the ignition switch is placed in the KL15 or KL50 positions, Fuse 34 is provided with power. Fuse 34 supplies the wake up or on signal to the EMS2000. Upon receipt of the "ON" signal EMS2000 supplies a ground signal from Pin 97 to the Main Relay. The ground signal energizes the Main Relay, supplying operating power to the following fuses:
- F02 - EMS2000, Fuel injectors, Crankshaft sensor, Ignition coils
- F03 - Camshaft sensor, O2 Heaters, Engine Cooling Fan, A/C Compressor Relay, Purge System
- F04 - Automatic Transmission controls
- F05 - Engine Coolant Fan
Workshop Hint
The Main Relay remains energized for 5 Minutes after the key is shut off. Before disconnecting connections to EMS2000, wait 5 minutes or remove Main Relay.
Workshop Hint
Always check current Wiring Diagrams for complete description of power supplies.
The Main Relay supplies power to the following components:
- EMS2000
- Ignition Coils
- Auxiliary Fan
- Fuel Injectors
- LDP
- ECVT/GIU
- Crankshaft Sensor
- Camshaft Sensor
- O2 Heaters
Use the Manual With the Right Hardware
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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