Push Start Button, electrical diagram - check please Options

[pittfirefighter]

Ok so i got my button in! but i need someone to verify that this will work...

Red box is a 12V source that gives 9-14V when the car is on and Running (W on ecu, 5th pin on 2nd harness)



push it once with clutch in should start the car... push it again should turn the car off

push switch is a momentary switch - it does not stay locked in position

all relays are in their open positions

This post has been edited by pittfirefighter: Dec 27, 2009 - 10:18 PM

[pittfirefighter]

updated diagram

[BloodyStupidDave...]

updated diagram

Okay, so what we have here is (numbering the relays from top to bottom and left to right):

Push and hold the push button: energisies the colis for relay #1 (latching relay) and #2.

Current flows from the posivie terminal of the battery through the switch for relay #2, the switch for relay #3, through the clutch switch (when the clutch is fully depressed) and through the coil for relay #4.

Th current flowing through the coil of relay #4 in turn closes the switch for relay #4, which allows current to flow from the +ve terminal of the battery, through switch of relay #4 to the starter motor. The starter motor turns, causing the engine to crank and start, at which point the red box (pin 5 of the ECU) goes from open circuit state to +ve voltage.

Current flows from pin 5 of the ECU through the coil of relay #3, breaking the circuit at relay #3 switch, which in turn stops the current flowing through the coil of relay #4, causing the switch at relay #4 to open and the starter motor to stop turning.

At this point, relay #1 is latched (switch is closed), relay #2 is energised (switch is closed), relay #3 is energised (switch is open), relay #4 is un-energised (switch is open), ACC, IGN and pin 5 are all +ve.

Releasing the push switch causes relay #2 to be un-energised (swich opens), which has no effect.

Pressing the push switch a second time causes relay #2 to energise (switch closes), which has no effect, and the ratchet-and-cam locking relay #1 to switch states (so that the switch is in the open position again).

This causes the ACC and IGN lines to become open circuit and presumably causes pin 5 of the ECU to go open circuit also.
With IGN open circuit, the engine and most of the electrical systems will shut down.

At this point, relay #1 is unlatched (switch is open), relay #2 is energised (switch is closed), relay #3 is un-energised (switch is closed), relay #4 is un-energised (switch is open), ACC, IGN and pin5 are all open circuit.

There is a minor problem here, in that if one were now to depress the clutch, the starter motor would crank. This could be solved by powering the left-side of the relay #2 switch from IGN rather than from +ve battery.

Releasing the push switch causes relay #2 to be un-energised (swich opens), which has no effect. At this point everything is back to its initial state.

One other advantage with using the double-press to start the engine (and having a timeout function) is that then a single press could toggle te ACC circuit on and off, which is exactly the same functionality on the factory-fitted Toyota start buttons.