Fried TCM/ECU?

[maktheknife]

My son bought his first car a a few months back, a '98 Legacy GT wagon. Since then we found out it had a blown head gasket. No problem, a great father and son project. Aside from this issue, the car ran great. We replaced the head gaskets and put the engine back in. Connected up all the hoses, connectors, etc. He turned the key and she fired up first time. Now the problems start. He went to fill up his tank and on the way the car stalled. It wouldn't start and the dash lit up like a Christmas tree. By the time I got there his friends were hovering over the open hood. When I got there the AT Temp light wasn't blinking but fading in and out, like a brown-out at home. the ABS pump was clicking like a cheap timepiece. Disconnecting the negative terminal settled the car down and all the lights were fine. Of note, the temp gauge maxed out and the fuel gauge was buried below 'E'. I checked everything and tried to start it again. Same thing, light show and clicking. Disconnected the battery again. I reached under the air box and made sure the connectors were all connected. My son being who he is, tried to start the car again. This time she turned over.

Sorry for the long post but I thought that was relevant information. Anyway, at this point the tranny (A/T) only shifts from 1st to 3rd. It does so at about 5500 RPM and really bangs into gear. Lifting off the throttle yields no engine braking at all. I hooked up my OBDII reader and found no codes. However, I connected the two green connectors and then tried again. Oh boy, jackpot. I got the following:

p0130 Front Oxygen Sensor Circuit Malfunction
p0136 Rear Oxygen Sensor Circuit Malfunction
p0500 Vehicle Speed Sensor Malfunction
p1100 Starter Switch Circuit Malfunction
p1101 Neutral Position Switch Circuit High Input (A/T)
p1120 Starter Switch High Input
p1121 Neutral Position Switch Circuit Low Input [AT Vehicles]
p1540 Vehicle Speed Sensor Malfunction 2

Now, I figured we couldn't have such bad luck that all those went south at once. We checked under the hood again and I found one connector which wasn't seated all the way. From the service manual it appears to be connector E1. My question is, when I checked the connections when the car wasn't starting could I have fried one (or both) of the computers? The battery was connected and the ignition on (my son was in the car). I'm thinking about just replacing the TCM and hoping for the best. Right now we have the FWD fuse installed otherwise sharp turns are no fun at all with the TCM thinking both speed sensors are shot. I'd appreciate any suggestions/opinions/incantations you have to offer.

Thanks.

[jey]

Unplug that green connector. It puts the ECU into diagnostic mode.

[maktheknife]

It was unplugged as soon as I pulled the codes.

[Huffer]

Bad alternator or ground issue? Sounds like a harness that has the O2 sensors + speed/backup/neutral switches hooked into it isn't hooked into the main harness.

I'd check all the connections again and reseat everything. Also check the ECU plugs for any moisture/damage...

[anothernord]

I beleive (not 100% sure) that connecting the green connectors will make the ECU show all the historic codes, not necessarily the ones that are current.

Also, grounding wires are VERY important. If something isn't grounded you'll have lots of problems. You might want to look into an ebay grounding kit anyway; to ground the starter, block, trans, etc straight back to the battery.

[maktheknife]

Thanks for the replies. Well, it's fixed. We had to replace the upper radiator hose today and while the hood was up my son asked me how important grounding was. As I was explaining things to him I showed him the ground connection that's on the intake manifold. Ad I tugged on the wire the damn thing moved. I was able to remove the bolt with my fingers. DAMN!!!! A wire brush, some WD-40 and a little hand torquing and everything was working perfectly. I was ready to replace the ECU and TCM. I had a feeling it was a grounding issue and I checked and double-checked every connector. I looked at this grounding lug and it seemed sound. Anyway, thanks again to everyone who replied.

[anothernord]

Awesome. Glad everything is working properly.

[maktheknife]

It's running great now but I still need to have the alternator tested. The Battery and Brake lights are on. Having the Alt tested tomorrow but that's a minor issue compared to what we had before. I still can't believe it was one loose ground connection. If anything, the two of us learned quite a bit about the "sooby". It'll be a great car for him and the N.J. winters.

[anothernord]

It's running great now but I still need to have the alternator tested. The Battery and Brake lights are on. Having the Alt tested tomorrow but that's a minor issue compared to what we had before. I still can't believe it was one loose ground connection. If anything, the two of us learned quite a bit about the "sooby". It'll be a great car for him and the N.J. winters.

Yep, I would recommend a grounding kit as well. Basically just a bunch of large gauge wires that ground things back to the negative battery terminal. It makes the whole electrical system more efficient and will reduce load on the alternator.

I'm glad you are working with your son on the car. I know I've had some of my best times with my dad while working on cars.