G4 Wiring and Installation Manual18
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6.8 ECU Hold Power Wiring
This wiring method is only used when an Idle Speed Control (ISC) Stepper motor is
wired.
This wiring method allows the ECU and engine management system to remain
powered after the key has been switched off. This allows the ISC stepper motor to be reset
to the appropriate position for the next start up. The ECU will shut down the system when
reset is complete.
The other alternative is to reset the stepper motor at key-on, which can cause excessive
over-rev on start up or extended cranking periods.
This wiring method is shown in the following diagram.
How it works:
1. The ignition switch is turned on, powering the ECU through the external diode.
2. The ECU powers up and switches the ECU and Main Relays on.
3. All systems are powered through the relays now and run as normal.
4. When the ignition switch is turned off, the ECU senses this through its Digital Input.
5. The ECU resets the stepper motor to its default position, then shuts off the ECU and
Main relays when it is ready causing the system to power down.
The following items must be set-up in PCLink Tuning Software when using this wiring. This
should be done on the bench before installing the ECU to prevent damage to the diode as it
will be powering the system until ECU hold power is set up.
· The appropriate Digital Input must be configured as 'Ignition Switch'.
· The appropriate Auxiliary Output (or Ignition or Injection channel) must be configured
as 'ECU Hold Power'.
· The ISC Control 'Stepper Reset' function should be set to 'Key OFF'.
The correct operation of this wiring system can be tested by listening for a pause of a few
seconds between switching the key off and the ECU and Main relays switching off. The ISC
stepper motor may also be heard operating during this period.
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