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Discussion Starter · #1 ·
First time posting, I have used this website a lot to help with my build but this time I haven't been able to find the exact information I need. Thanks for everyone's contributions to the forum, if you read below and can help me out thank you in advance.

This issue is around first time start up of a new motor build into a swapped gc8 chassis. The wiring harness plus most mechanical parts are from a 2006 sti donor, there is minimal wiring splicing done, it's at the door's or lights but all engine harness connections are untouched and are in good shape. Donor car was written off from a rear end hit.

Issue, car will crank but will not start. Security light is off on the cluster so immobilizer should be good, I have the correct key/antenna and all components from the donor car. Every other light on the dash is on, cruise control blinks.

No spark or fuel when cranking. Plugged in scanner and cannot connect to the ECM. I do get fuel pressure though so pump is turning on.

All fuses are good, have rechecked over 10 times, looking at connections through the fuse as well as checking for voltage on either side of the wires in both engine bay and dash fuse box.

Replaced main relay - although likely did not have too.

I have checked all grounds and all pinout grounds to the ECM, here's the details below but all test below 10ohms which tell me those are good grounds at the ECM harness. Grounds that attach to the dash bar or the side of the interior cab are in good shape too, all have been sanded and redone and are measuring below 5ohms. No interior in the car right now so it's easy to get to everything.

PWR supply grns - B135 pin 4 9.2 ohm
B135 pin 1 9.3
Ignition grn B135 pin 12 3.6
Control system grn B137 pin 1 and pin 2 8.2 ohm.



Main relay coil, has an lgw (light green with white stripe) wire. This connection turns the coil on to close the other two contacts then continues to provide pwr to the ecu, per the 2006 wiring diagram I am using, goes to pin 23 on connector C.

With the ECM unplugged, main relay plugged in, I see 12.4V at all 6 connection points to the main relay with my meter. When I plug the ECM in, I still see 12V at each relay connection, but on the coil it drops to 0.8V. This lgw wire I cannot trace to the ECU harness.

I have only been able to find the 2005 sti ECM pin out online. The wire diagram I have says the lgw wire from the main relay should run to ecu pin B136 pin 23. When I check that connector the wire is pink and I have no continuity to the lgw wire at the main relay.

What would cause the voltage drop when plugged into the ecm, bad ecm knowing that all the grounds are okay? I need to measure the resistance of that connection once i figure out what the correct pin is.

This pinout also says that blue red wires should bring supply power to the ecm through pin B5 and B6, the colors do not match on my ecm harness and I see no voltage on those pins.

I am hoping that the diagram for the 2006 is different and then I can properly trace the power connections if someone can help me get a copy that it would be greatly appreciated!

I also opened up the ecm to look at the board, no visual signs of damage.

I removed the dash bar and hvac units. The harness looks fine, no pinching or any look of damage so I am pretty confident I do not have a wiring issue between the main relay and ecm, it's a small run between there.

Any support to find a 2006 ecm pin out and thoughts/ idea's on what to check next would be great!
 

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Discussion Starter · #3 ·
Everything except the cluster is from the donor car. I was pretty sure this was an immobilizer issue at first as well. I spoke to the local dealer and they said if the security light on the dash goes out with the key on then the immobilizer is happy. They also mentioned the scan tool should still connect because they need to use the obd port to program new keys.
 

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Discussion Starter · #4 ·
Unfortunately I am not getting many response here but I have a small update and questions.

I talked to an electrician at work about my problems. He's not an expert at cars but one thing I learned is that when a relay coil is on there is voltage drop on one side and that 0.8V is a typically transistor voltage drop. So this means the ECM is commanding the main relay to turn on.

I am still at a serious loss of what to do next. I have checked every pin at the ECM for resistance/continuity back to each component/module. I have good readings between the immobilizer, all of the power connections, to the OBD2 port. I have checked all power and grounds to the immobilizer and too the key less entry module. I feel I have completely exhausted looking for issues and have spent hours following wiring diagrams and checking pins.

Can anyone confirm, if you have an issue with the immobilizer, can you connect a scanner to the obd2 port?

I am also new to subaru's and tuning, but if the car had been tuned with an access port and not unmarried, would that prevent me from being able to connect a normal scanner?

Is there anyway the unmarried access port idea would cause a no start? What would happen to a tuned ECM if it had been without power for years?
 

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2007 Subaru WRX Wagon Ltd
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I'm actually having this same issue with a fully stock 2007 Subaru WRX Wagon Ltd. It was running just fine and as we drove down the highway the car just died... I've been troubleshooting this for almost 2 years. What I've found is that the A7 & B2 ECU pins have a voltage drop of 9v from one side of the Main relay to the other... I found that this was caused due to the Main Relay not fully grounding out via the LgW. When I ground the LgW wire at the main relay, the car starts and runs/drives fine without issue. My concern is that in the wire diagrams from the 07 manual shows that the ECU controls this grounding via a transistor, but I don't know what signals that transistor to ground out the Main Relay... If anyone could tell me that, I'd be grateful! Hope this helps your hunt...

This is where I got the manual.... WRX & STI Factory Service Manuals
 

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Discussion Starter · #6 ·
With the ecu connected and ignition on what voltage do you see at the main relay on the lgw wire?

What voltage do you see at the other 5 points of the main relay?

What your saying is that with the ecu connected you would still see 12v at the lgw white wire, instead of a voltage drop to turn the relay on so you need to ground it manually to turn on the relay. If that's the case I would start checking all the ground wires from the ecu for continuity back the battery.

I'm not sure what a7 and b2 are. But there are wave form inputs/outputs that with a normal multi meter you basically see the average of the wave so the voltage seems low. Might be no issue.
 
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