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V3/4 WRX & STi ECU power wiring information


Dairusire

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So, because this was a PITA for me, I'm sharing the knowledge I've gleaned from this. Anyone else is welcome to fill in the blanks that I've missed.

In short the V3/4 I bought had an issue with ECU not starting. 

 

Now yes the issue is now fixed, and I found what my problem was. It was a fuse short. Apparently I missed it on the first pass. Somehow.

 

In any case, if you have the same issue as I did, where a car will turn over, dash will light up, but fuel pump won't prime and lastly the ECU won't turn on, don't go start pulling this apart to find the issue. Just check Fuse #11 in the drivers (RHD) side fuse box

 

x5sCnem.png

 

The bottom plugs in this image are the ones you're looking for. 3 plugs.

87535096_8a94b09395_b.jpg

 

EJ20K

Input
112 Green Signal wire to relay that switches on ECU power on pin 113 (not joking)
113 actual switched ECU power that turns ECU on

114 ECU Circuit power 
111 Ignition SW
37 Airflow sensor signal
36 Airflow sensor ground
38 O2 Sensor
33 crank angle sensor +
34 crank angle sensor ground
35 cam angle sensor
40 water temp sensor
39 knock sensor
48 throttle sensor power
46 throttle sensor signal
45 absolute pressure sensor
22 car speed sensor
43 exhaust noise sensor 1
31 Air conditioner SW
23 Starter SW
32 Neutral SW
115 sensor-type ground
105 injector ground
110 power type ground
116 ??
106 ignition ground
24 intake temperature sensor
28 intercooler spray auto SW
7:44
output

104 injector #1
101 injector #2
102 injector #3
103 injector #4
1 ignition signal 1,2
2 ignition signal 3,4
107 IDC valve open
108 IDC valve close
26 canister purge solenoid
8 ? pressure solenoid
5 atmosphere switch solenoid
17 radiator fan relay 1
25 radiator fan relay 2
4 fuel pump relay
11 aircon relay
3 check engine lamp
12 exhaust sound warning lamp
27 engine rotation signal
20 select monitor send
21 select monitor receive
41 test mode connector
42 reed (lead?) memory connector
30 AT ?
18 AT air amount

 

 

So if you've checked the fuse and thats fine or you've replaced it and it's still not working, check the relay. 

 

The relay is located under the dash, to the right of the go go juice pedal, and is brown. Photo below for context. 

 

EJDpuOz.png

 

Now, the wires coming into the relay are

 

2x black with red stripe down the middle (permanent 12-14v live)

1x Yellow w/ light blue down middle (switched 12-14v to ECU from Relay)

1x Yellow w/ red stripe down middle (switched 12-14v to I assume Fuel pump relay? I don't know.)

1x Green wire (switching signal to turn off/on relay from ECU)

1x Black wire (ground)

 

Now, I have ZERO clue as to why Subaru insisted doing it the way they have. Essentially there is switched power from the ignition, which runs through  fuse 11, that goes to the ECU on pin 114, that then turns on the signal wire on 112 so it can switch ON the relay and send power back to the ECU on Pin 113.... 

Yeah. So there's that 0.o

 

Enjoy your misery ???? 

 

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