Where is the ECU?

rallylegacy57 · Post by **rallylegacy57** » Sat Feb 18, 2006 4:06 am

The ECU on my 1990 Legacy is on its way out. I have searched the car top to bottom with no luck. I have found the auto transmission contol module, the cruise control unit, and just about every other electronic gizmo on the car but I have yet to find the computer. Can someone lend me some advice on where it might be. My car is a 1990 Legacy L AWD. Thanks in advance.

Binford · Post by **Binford** » Sat Feb 18, 2006 4:23 am

Check the steering column.

rallylegacy57 · Post by **rallylegacy57** » Sat Feb 18, 2006 4:31 am

Binford wrote:Check the steering column.

So it is right near the Transmission control module then??

Binford · Post by **Binford** » Sat Feb 18, 2006 4:49 am

I'm pretty sure it should be the same as my '91 SS. Left of the column, you should see four yellow plugs into a box. That's it.

rallylegacy57 · Post by **rallylegacy57** » Sat Feb 18, 2006 5:22 am

Thanks I will check that out tomorrow.

rallylegacy57 · Post by **rallylegacy57** » Sat Feb 18, 2006 5:28 pm

Ok checked this morning. The ECU is not by the steering column. The transmission control module is on the left side of it but there is definitely no ECU there. Anyother ideas? I am about ready to rip what is left of the interior out to find this thing.

vrg3 · Post by **vrg3** » Sat Feb 18, 2006 5:44 pm

http://bbs.legacycentral.org/viewtopic.php?t=2356

Why do you say your ECU is on its way out?

rallylegacy57 · Post by **rallylegacy57** » Sat Feb 18, 2006 9:03 pm

vrg3 wrote:http://bbs.legacycentral.org/viewtopic.php?t=2356

Why do you say your ECU is on its way out?

Thanks for the link. I think it is on its way out because the car was running fine and all the sudden started running crappy and the check engine light would come on. Then 2 minutes later the light would go out and the engine would run fine again. I got several diagnostic checks to run from my dad who works at a repair shop. Everything is pointing to partial ECU failure. Now the car is constantly running rich and the ECU is throwing error codes for the 02 sensor, TPS, MAF, and Knock Sensor. If you have any other ideas I would be appreciative but for now I will do a complete check on the ECU because that is what I feel it is.

Imprezive · Post by **Imprezive** » Sat Feb 18, 2006 11:11 pm

So you still cant find the ECU? It is to the left of the steering column, under the dash, and it is behind a big metal plate that is is bolted to. To the left of the metal plate you will see 4 yellow connectors they are connected to the ecu.

rallylegacy57 · Post by **rallylegacy57** » Sat Feb 18, 2006 11:45 pm

I am going to go digging around under there somemore. It seems my car has had some hack job wiring that is cluttered and you can't see the ECU in the location it is shown explained and shown in the link that was provided. I will have to shove some of the wiring out of the way to get to that spot.

free5ty1e · Post by **free5ty1e** » Sun Feb 19, 2006 11:55 am

's probably part of your problem. Once you get in there and locate it, make sure none of the ECU wires are hacked into improperly or something.

Then check all power and grounds for aftermarket stuff, and if you still don't have any answers measure the signals from the sensors in question (from the CEL codes) with a voltmeter and compare to specs at idle.

rallylegacy57 · Post by **rallylegacy57** » Sun Feb 19, 2006 8:48 pm

free5ty1e wrote:'s probably part of your problem. Once you get in there and locate it, make sure none of the ECU wires are hacked into improperly or something.

Then check all power and grounds for aftermarket stuff, and if you still don't have any answers measure the signals from the sensors in question (from the CEL codes) with a voltmeter and compare to specs at idle.

Located the ECU and pulled it down. All the wires going into the ECU are not touched. I have checked all the signals to the sensors and the grounds for the codes being sent out. Any other ideas on what could be wrong. Thanks again for all the advice and ideas.

vrg3 · Post by **vrg3** » Mon Feb 20, 2006 12:36 am

Here's a check I'd try:

Clean the MAF sensor carefully.
Disconnect the oxygen sensor, throttle position sensor, and knock sensor.
Disconnect the battery's negative terminal and hold the brake pedal for a few seconds.
Reconnect the battery and then drive around gingerly for a while.

It'll buck every time you move the throttle too quickly, but other than that the car should drive okay. It should throw trouble codes 22, 23, 31, 32, and 42.

free5ty1e · Post by **free5ty1e** » Mon Feb 20, 2006 3:07 pm

...Now that's an ECU test.

rallylegacy57 · Post by **rallylegacy57** » Tue Feb 21, 2006 1:26 am

slight problem the engine won't stay running with the MAF disconnected.

magicmike · Post by **magicmike** » Tue Feb 21, 2006 1:41 am

he didn't tell you to disconnect the maf. he said clean it.

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Where is the ECU?

Where is the ECU?