97 Impreza OBS 4EAT. Need help with (Seemingly) Poor connection to TCU

[QuiteImprezed]

Hi Everyone! First post here, sadly its a request for advice..

I have a 97 Impreza Outback Sport which for the past few months I've battling the "AT Oil Temp" light of death..

Through a combination of OBD2 scanner and doing the TCU diagnostic handshake.. I have been able to retrieve the codes suggesting a few issues with the ECU talking to the TCU.
the FSM has given me a few tests to do with my MultiMeter, and these all passed (except for one regarding checking resistance on the speed sensor line, but I think this is unrelated so I won't elaborate for now).

Something I notice though is that sometimes the AT OIL TEMP light doesn't actually light up properly when the key is turned but the engine is still off.

Moving the wires around on the TCU will cause the AT OIL TEMP light to flicker.. So its a poor connection.. cool..
Problem is.. I'm sort of stuck here...

• I've de-pinned the connector and checked/cleaned each individual Pin, but this had made no difference (there were no signs of corrosion, all pins looked shiny like new).
• I'm almost certain that the issue is at the connector to the TCU end, not further up the harness going by where the AT OIL Light responds the most to my interaction with the wires..
• I took the TCU out of the car and opened it.. all of the soldering looks fine and I can't see any signs of a poor connection on the board.. though this is still where my suspicion lies, as gently squeezing the connector can also make the light flicker.

I may have other issues elsewhere.. but for now I feel like this is the area I need to focus on as it's easy to investigate and observe the connection issue just by reaching under the steering column and move the wires with my hand while watching the light on the cluster turn on and off.

If anyone could offer some advice, or insight I'd be really grateful.

Thanks!

[moosens]

That board that looks like all the soldering is up to spec and functional - but has a flicker still - I’d be considering baking the board but I’m no expert and only going by what I am pretty sure I’ve read a few times. 
 

Maybe get a jeweler’s eye or magnifying glass etc and check those soldering points especially at the connectors. The usual weak spot. 
 

It’s a 97 OBS the S for Sport so surely you’ve been thrashing it about once or twice, no ? All the wiggling and jiggling. 
 

Good luck with it. 

[lmdew]

Grab a TCU from the yard, you can always take it back for credit.

[idosubaru]

Taking it apart - can you check continuity from the connector wiring harness side to a point on the circuit board of each pin as far down stream of the connector as possible. maybe also why wiggling or pressing it to the side so to speak. 

If you have access to any used Subaru parts All 1995-1998 4 cylinder 2.2 liter and 2.5 liter, Outback legacy Forster Impreza TCUs all readily swap.And 99 Outback’s and Legacys.  I think even a FEd TCU is plug and play lol

[QuiteImprezed]

5 hours ago, moosens said:

That board that looks like all the soldering is up to spec and functional - but has a flicker still - I’d be considering baking the board but I’m no expert and only going by what I am pretty sure I’ve read a few times. 
 

Maybe get a jeweler’s eye or magnifying glass etc and check those soldering points especially at the connectors. The usual weak spot. 
 

It’s a 97 OBS the S for Sport so surely you’ve been thrashing it about once or twice, no ? All the wiggling and jiggling. 
 

Good luck with it. 

I think likely it would of been caused by me trying to unplug the connectors in the first place, they were stubborn and I had to be quite rough with it.
I had considered giving each of the pins a quick bit of heat with the soldering iron to re-fuse any pins which may have been damaged.
But this car is really teaching me not to do something unless I'm sure, as a lot of times lately I'm breaking things as I fix them.
Thanks for your advice!

 

 

5 hours ago, lmdew said:

Grab a TCU from the yard, you can always take it back for credit.

I'll keep an eye out, but that might be difficult for me. The Impreza is USDM, but we are actually in Taiwan... the language barrier makes it a bit hard to talk to wreckers here, not to mention I'm not even completely sure if wrecking yards are a thing here haha. Thanks for the suggestion though.

 

 

4 hours ago, idosubaru said:

Taking it apart - can you check continuity from the connector wiring harness side to a point on the circuit board of each pin as far down stream of the connector as possible. maybe also why wiggling or pressing it to the side so to speak. 

If you have access to any used Subaru parts All 1995-1998 4 cylinder 2.2 liter and 2.5 liter, Outback legacy Forster Impreza TCUs all readily swap.And 99 Outback’s and Legacys.  I think even a FEd TCU is plug and play lol

Ok! thanks for some directions, I created this post because I'm starting to feel pretty lost with this. That's a good idea, If I get a chance I'll have a go at it today, but its already getting dark and the mosquitoes have started their shift.
As mentioned in the paragraph above I'm located in Taiwan.. Oddly there was an Impreza craze here in the 90's so there should be some Phase1 4EAT TCU's about.. just finding them is hard. Sadly, as far as I know there were never any Legacy's or foresters.. haha otherwise I would of already tracked down the forester shocks for a cheap lift kit.

Really appreciate the suggestions from everyone.

[QuiteImprezed]

Just an update...
So having the TCU open I checked the continuity of each of the pins and various places on the board.
I wasn't able to find any clues while wiggling or squeezing the connector or pins, unfortunately.

after a quick "spray and pray" with the contact cleaner, I plugged it back into the car turned the key to the on position (engine off) to check the bulbs on the cluster, and sure enough there was no AT light appearing at all.
Got down under the steering column and moved the wires around, etc. and like before I was able to make the AT light flicker as I moved the wires in certain positions.

Narrowing down the most sensitive area I was again confident that it was the TCU side connector, not the wire..

So, I figured "bugger it" and fired up the soldering iron. With a tiny bit of solder I heated up each connector pin on the PCB quickly but just enough to see the solder turn to liquid and hot enough to stick to the pin, and then remove heat and onto the next. I could only do this on the underside, as the top side had far too many components in the way and even with a narrow solder iron I was still unable to reach the points.

After a quick spray with contact cleaner to remove any flux residue, I took it back to the car, plugged it in and switched the car on (engine off).

The AT light came on instantly and stayed on. Moving the cables around the light remained on.. however there was a certain point where the light would still flicker, but this was very minimal. It was a huge improvement.

Started the engine and the AT light does its usual on for 1 second and then turned off.. and remained off for the 30km drive into town and back with a few starts and stops. This is the standard behavior of the light, for those not familiar with phase 1 4eat.

No CEL, no flashing AT Light codes.. no random on and off while driving.
So I'll take this as a win for now.. Though this isn't the first time this car has had me feel like I cracked the issue only to start again the next day, so I think I'll wait a few more days before I celebrate.

Hope my dilemma can help anyone else that may have a similar issue.
 

[lmdew]

Did you record the TCU Part Number information?

If you end up needing one, I may be able to help.

[QuiteImprezed]

28 minutes ago, lmdew said:

Did you record the TCU Part Number information?

If you end up needing one, I may be able to help.

Thanks, will do!

I went to start the car this morning and already the bulb wasn't lighting up with the key in the on position, jiggled the wires till it appeared.. then started the car and she was fine for the rest of the day. Next time I decide to open the TCU again I'll get the part number, but for now I'll leave it as there is other maintenance to be done and not enough time in a day.