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Old 09-16-2008, 08:30 AM   #1
camaroz1985
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Default Electrical Problems, Seems Like ECU is not Powering On



Ok so here is what I have found. I'm hoping someone can help me diagnose this problem.

Background:
98 RS being swapped with 2007 WRX engine. Wiring is complete. I was pretty thorough (or so I thought), when checking and double checking connections.

Symptoms:
When I turn the key on I get no CEL, no Fuel Pump, and the fans run continuously (Test Connector is unplugged).

Using the Diagnostic section of the service manual I have found that all power (backup (B135-5), and ignition (B135-19)), as well as grounds (engine, body, and sensor, which I believe are through the ecu because I only got the sensor grounds when I had the ecu in) are good. The problem is I only get 2.5V to the main relay pin 3 (also at B134-7, and B135-2). The diagnostic section says this should be between 10-13V. Also there is no power to the FPC (should be 0 or 5V on the one pin, and 10-13V on the other). I also can not connect to the ECU using Accessport.

Any ideas on what might be my culprit? I thought I was ready to try to start it up, but I get this. I'm hoping for something stupid, and not a bad ECU.
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Old 09-16-2008, 08:35 AM   #2
turboL
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get the CEL to come on is your first task. If your cel doesn't come on when the key is on and engine is off. Either your ECU is not getting power or the MIL wire isn't connected right.
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Old 09-16-2008, 09:20 AM   #3
camaroz1985
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Could it not come on if something was wrong with the ECU?
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Old 09-16-2008, 09:26 AM   #4
Jaxx
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yes but if you have to replace the 07 ecu your in to another whole mess of trouble with the imobilizer
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Old 09-16-2008, 09:39 AM   #5
camaroz1985
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That's what I'm trying to figure out (and what I fear).

Here is what I have:

12V Constant on B135-5 (Backup Power)
12V with IGN on B135-19 (Ignition Power)

Those should be the inputs to the ECU if I read the diagram correctly.

Output from that should be 12V to B134-7 and B135-2, and that is what goes to the Main Relay. On those pins I am only getting 2.5V.
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Old 09-16-2008, 03:35 PM   #6
ciper
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I think the hard way is the only way - unplug it from the ECU and check the voltage one connector up the line. If its 2.5 leave that unplugged and move another connector up the line. Keep unplugging items from that chain until you find 12 volts.

This may sound dumb but are you sure the battery isn't low? I've seen some goofy things when the battery was dead from sitting too long during a swap.
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Old 09-16-2008, 04:52 PM   #7
camaroz1985
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Quote:
Originally Posted by ciper View Post
I think the hard way is the only way - unplug it from the ECU and check the voltage one connector up the line. If its 2.5 leave that unplugged and move another connector up the line. Keep unplugging items from that chain until you find 12 volts.

This may sound dumb but are you sure the battery isn't low? I've seen some goofy things when the battery was dead from sitting too long during a swap.
No, battery reads 11.98V or something like that.

I heard on RS25 that you need to switch two pins ground for power in the main relay and fuel pump relay. I confirmed it with the diagrams and will give that a shot tonight. Hopefully I don't have to go through this pin by pin to find the problem.
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Old 09-16-2008, 05:40 PM   #8
ciper
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Thats a dead battery.

12.65V
100%

12.45V
75%

12.24V
50%

12.06V
25%

11.89V or less
Discharged

From http://www.batteryuniversity.com/partone-13.htm
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Old 09-16-2008, 05:48 PM   #9
turboL
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yeah your battery is beat sauce. the above post is exactly right.
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Old 09-17-2008, 01:14 AM   #10
camaroz1985
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It was the two terminals switched. Pin 1 on the Main Relay needed to be power, and Pin 3 on FP relay needed to be ground. Did that and pump primed, CEL came on, and was able to communicate with the ECU using Accessport.

Thanks for the help and suggestions.
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Old 09-17-2008, 07:25 AM   #11
turboL
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you should still get that battery replaced or recharged.
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Old 09-17-2008, 10:10 AM   #12
camaroz1985
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Its on the charger now. It has been sitting since June so I'm sure it lost a bit of a charge. Thanks again.
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