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Subaru ECU hold power not working

Ryan C

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Hey guys... OK I'm a bit stumped here. Here's what I know: My G4 needs to remain powered on after the ignition is removed for a few seconds. This allows the ISC motor to park. (Ver 5/6 ISC) - In order to do this, a digital input (Ignition sw) needs to be configured and wired. (done) - Then you need to setup an Aux ign out to, presumably, ground the other side of the main relay coil. - Sequence of events as I understand it: Link senses the 12V ign sw drops and pulls a low down on aux ign #6. This keeps the relay energized until the ISC can park. A few seconds later, ECU floats the aux ign #6 and the main relay is de-energized. Great! But... - According to my Subaru Version 5/6 wiring diagram, one side of the main relay coil is tied to a ground. The other side (that actually goes to the ECU) would need 12V to energize. On that pin, 'self-shutoff control' puts 12V on it to energize the main relay. - The Link wiring diagram for setting up the ECU hold power assumes that one side of your main relay coil is not tied to ground. - I don't want to re-wire the main relay. I'm trying to contain everything to one jumper harness between the stock, unmolested, engine harness and the Link. Since I'm still in the 'beta phase' I like being able to swap back to the stock ECU. So I thought I had a solution using two relays. However, somewhere along the way it failed to work. Below is a diagram, criticism is welcome ;)a> I was trying to use the ign sw input to trigger the relays. I'm not sure how loaded down that circuit gets when the starter is engaged. Since the OEM ECU uses B136 pins 8/9 as 'control power', I figured they would be suitable for powering the box. Thanks! Ryan


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  • 2 weeks later...

As I typed the response I was thinking to myself that I bet Ryan has a wire in model.

I'm not too worried about modifying the loom to suit what I want, and if I move to a more modern solenoid type of IAC I'll rewire as I need to. I wasn't too worried about the knock control being built in as I already had a knock block anyway, this coupled with two sensors gives me what I need in that respect.

Whether it is hot or cold mine will start with the same amount of cranks (roughly speaking) there is no noticeable difference when it is hot. I am obviously still running the stock IAC setup, but have a set of 700cc injectors in place of the stock 440's.

For pre-crank prime I have 2ms for ECT of 80 and then 0ms for 90 and above. Crank enrichment is 15ms for 80 and 5ms for 90 and then 0 for 100 and above. Which from memory were the stock for the V5 maps. I've found that the hot engine requires a bit of fuel initially to help stabilize the idle so I wasn't too worried about having the extra little bit in there for start and then let it decay off post start. My closed loop lambda for idle is 15.4 and I find idle rock solid.

So far I'm more than happy with the plugin, it does what I need, accepts the input from the LC-1 wideband setup, the IAT, runs gear dependent boost tables, and controls the water/meth injection (rudimentary boost versus throttle position). 



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You engine should start as well as it did with the factory ECU. Adjust your pre-crank prime and crank enrichment numbers, by the sounds of it the engine needs more fuel than its currently getting.

'I'm thinking the reason is because the Link couldn't put a ground on the power hold output fast enough when it detected a change in supply voltage.' - the ECU turns on the hold power output on as soon as the DI sees the ignition signal (the output is already on when the key is turned off). If you don't have a DI set to ignition switch, hold power won't work, this could be causing your troubles?



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  • 11 years later...
then it is a plug and play wrx 5/6 g4 firmware 4.10.2
my subaru is a gt 2000 with a wrx sti engine
and a mix of harness 2000 and wrx, with the oem ecu the car runs.
I think I just miss the wire for (the ecu hold power)


here is my ecu


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