This EFI Main Relay circuit is used exclusively on applications equipped with the stepper type Idle Speed Control Valve. This relay is powered by the ECU rather than the ignition switch to allow control of the relay for approximately two seconds after the ignition is switched off. This allows the ECU to step the ISCV back to engine restart position after ignition power down.
When the ignition switch is turned on or engine cranked, the ECU receives a voltage signal at the IG SW terminal. This causes the ECU to supply current from the MREL terminal to the EFI Main Relay pull-in winding. The pull-in winding is grounded directly to the vehicle chassis. ECU BATT voltage is supplied from the EFI fuse on these applications.
When the ignition switch is turned off, the ECU will maintain current flow through the EFI Main Relay pull-in winding for a few seconds after power down to allow time to reset the stepper ISCV.
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