Main Relay Circuits

Toyota utilizes several different EFI Main Relay circuits depending on application. These circuits can be categorized into four distinct types.

1) Dual contact EFI Main Relay, ignition switch controlled

2) Single contact EFI Main Relay, ignition switch controlled

3) Dual EFI Main Relays, ignition switch or ECU controlled

4) Single contact EFI Main Relay, ECU controlled

Generally speaking, the EFI Main Relay supplies current to the following major circuits:

• Injectors (dual relay or dual contact relay only)

• Circuit opening relay (power contact and pull-in windings)

• Air flow meter VB circuit (when so equipped)

• Output Actuator Vacuum Switching Valves (VSV)

- Fuel Pressure Up (FPU)

- Exhaust Gas Recirculation (EGR)

- Throttle Opener

• ISC motor/solenoid windings

• Check connector +B terminal

Because the EFI Main Relay supplies battery voltage to the +B terminal of the check connector when the ignition switch is in the run position, this is an excellent place to perform a quick check of the relay function.

What Efi Main Relay

Dual Contact (Single Relay), Ignition Switch Controlled This EFI Main Relay configuration is used on the Conventional eFi system. It uses separate power contacts to supply current to the fuel injector/ignition circuits and the ECU/circuit opening relay circuit. This limits current flow that the ECU power contact must handle.

This configuration improves the reliability of the relay, reduces possible voltage drop, and also isolates any inductive noise from the injectors to the EFI Computer by utilizing the battery as a large capacitor.

Toyota Camry Efi Main Relay

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