MoTeC M150 ECU power question

Hi all,

I’m trying to verify a wiring approach to a factory Supra relay system.

The factory mkiv Supra has a battery constant that relies on a 12V ignition switch (key) which then sends a 12V signal to the main relay, which in turn activates 12v switched power throughout the EFI relays.

Since I am Not using a PDM, I want to be sure to wire the m150 power correctly so that the key turns, activates power and remains on when cranking.

im attaching a photo of the factory wiring.

Depending on the firmware package you are using the M1 should have a specific ECU Power Relay function which is intended to control this type of relay arrangement.

So OEM pin 33 would be to any bat +ve pin of the M150, say C26, this will NEED a diode to stop the ECU powering the ignition circuit after the key is switched off. You can see in the diagram the OEM ECU has an onboard diode for this.

This will power the M1 which will then immediately enable whichever resource is assigned under ECU Power Relay. This should either be a low side ignition or low side injector resource, do not use a half bridge as these rest low while the ECU is not powered.

The output from the EFI Relay seems to be wired to OEM pins 31 and 32 in the diagrams provided, so these would go to the other two bat +ve pins of the M150, B13 and B19.

The M-Rel relay requires a 12V to enable. I thought low side injector and ignition go to ground? Imagine a HBO was the only way to have the ECU send 12V to the M-Rel relay?

The firmware doesn’t have anything but the build out for a transmission. Everything else is going to be setup.

Yes you're correct, my mistake. ECU Power Relay allows you to use a half bridge resource and you can set the drive type to high side. This will provide bat +ve to switch the relay.

The half bridges allow a path to bat -ve when the ECU isn't powered but this won't matter in this case.

Are you using GPR firmware or something else?

I’ve also thought about just wiring the factory ignition switch to the M-Rel directly to provide the 12V switched power and then running the main EFI relay to the ECU Battery 12V points.

That should in essence do the same thing. Thoughts?

What using the ECU Power Relay function allows is for the ECU to remain powered after the ignition is switched off. This could allow cooling fans or pumps to operate post engine shutdown to cool things off. When that is done, the ECU can turn itself off.

In addition to what David mentioned, depending on the your logging settings, allowing ECU control of main relay power can avoid issues saving logs.

So how about simply wiring it like this:

12V ignition switch to Motec M150 C26 for key on power

Using HBO to supply 12V to the M-Relay from the M150

Then wiring from the M-Relay 12V switched to B13 and B19.

This setup should in theory give me 12V from key-on to all 3 battery positives and when the key is put in ACC still supply power to the ECU off pin C26. Obviously, once key is removed and car is off, all switched 12V would cease. I think this would negate the need for a constant 12V to the M150 or the use of a diode. Thoughts?

I know the M150 does have a pin D12 for battery backup but have been told this isn't necessary.

What Dave said is correct, the power relay function exists so that the M1 controls it's own bat +ve supply.

Especially helpful when you are connected via ethernet as the M1 will stay powered while M1 Tune is connected even if the key has been switched off.

The M1 shouldn't require the power relay for data logging. Logging is pretty robust.

All of the bat +ve pins on the M1 are connected internally so the power from the EFI Relay at B13 and B19 will also be present at C26 after the ignition switch, this is why you need a diode.

Now that I look at the diagrams again C33 is not switched so this wouldn't be suitable otherwise the ECU will never switch off.

Looks like OEM pin 1 is from the ignition switch to the ECU via a 7.5A fuse, so this would go to C26 of the m150 (yes through a diode)

So just wire in a 1N4007 diode between the ignition switch OEM pin 1 and c26 of the m150 (single wire with diode inline)?

Use the HBO for the ECU power relay.

Main Relay then feed 12V to the remaining power pins?

I would allow for 10A of current through the diode, this gives you a bit of overhead since this circuit is fused for 7.5A according to the diagram.

Also maybe a dumb question, but I do not have a pin out for this specific m150 in a package file. Do I have to actually access this specific ECU on the bench to get the package off of it? I’ve been provided a license for it which I installed in m1 tune… but other than that no other file was provided to me.

You can download packages to your computer and look at them, even if your ECU isn't licensed to run them. Packages from MoTeC are available at

https://moteconline.motec.com.au/Package?rand_token=091921270624

If your license / package is a from a third party, then the MoTeC Partner should be able to provide you with a baseline package.

The mTune software won’t let me setup the ECU relay via a HBO. It’s only letting me choose low side…

So sounds like splicing the ign switch to MREL and a batt pos input will be way to go with a diode?

GPR and any GP based firmware will allow you to use a half bridge and set the drive setting to high side. This has been the case for a long time even if you were using a really old firmware.

Only available resources are listed so you may have all the half bridges assigned elsewhere.

If you're struggling it might be worth reaching out to your MoTeC dealer to assist.