TCU Codes

[mjm4jc]

Hello everyone,

So I've been trying to pull transmission codes on my 95 LX Wagon 2.2L using the handshake method. Unfortunately, it is not working. I read on some other forums that after going through the process, the last thing to do before the light flashes the code is to depress the gas pedal. I also read that some people are putting a ground pin in one of the connectors first, and then going through the process. I'm assuming that my Subie has the phase 1 4EAT trans? If so, can someone explain the correct/complete procedure? I did the handshake method on my daughter's 97 Impreza many years ago and don't recall ever having to depress the gas pedal or ground out any pins on any connector. But that was long time ago, and my memory isn't always that sharp. Please advise.
Thanks in advance,
Mike

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[mjm4jc]

Anyone????

[mjm4jc]

I probably should have posted this thread in the Transmission forum......my bad. I'll put it there.

[arse_sidewards]

I've always used this guide

https://www.surrealmirage.com/subaru/trans.html

Not sure if it applies to your '95 Impreza though. If you have the manual button it likely does.

[mjm4jc]

Thanks! I don't have the manual button, but I'll give it a try.

[mjm4jc]

Procedure didn't work unfortunately. Is this the procedure for earlier OBD1 vehicles? If so, I would need the procedure for the OBD2 vehicles. My scanner can't connect to the TCU to pull codes. It's a good scanner and even has vehicle specific software in it. I can troubleshoot the transmissions on all my other vehicles with this scanner, even my daughter's BMW, but it will not connect to the TCU on this vehicle. And even though my Subie is a 95, it has the OBD2 system. I can pull engine DTC's no problem. Please advise.
Thanks!

[Charlie-III]

I believe in the US, OBDII became mandatory in MY 1996 although some manufacturers started earlier. A lot of generic scanners are sketchy prior to 1996.

I don't have an answer for you, but figured I would give a possible reason why your scanner isn't pulling TCU codes.

[mjm4jc]

Much appreciated Charlie. Thanks!

[wtdash]

HI, have you tried this one, too: https://www.ultimatesubaru.org/forum...mission-codes/

Yes, it's the Phase 1 4EAT. As that was the 'transition' year to OBD2, it might be in between.

[mjm4jc]

Yeah I tried this one. But I am confused between steps 6 & 7. Does this mean that when I come to a stop I'm supposed to let my foot off the brake then press it again?

[wtdash]

I would consider step #7 to be like 'Part 2' of the process. It doesn't say to 'hold the brake pedal' when at #6 - 'Stop the vehicle'.

Edit: Also, is the CEL light on? If you have codes pending in the ECU there I'd address those before the TCU codes.

If the above doesn't work, I would disconnect the battery for ~hour to 'reset' everything. It won't fix issues, but might allow you to read the TCU codes?

Any symptoms or you just have the 16 AT Power flashes at startup?

[mjm4jc]

Ok thanks for clearing that up. No CEL light. I have the 16 flashes of the AT Temp light only on startup. I suspect I have two solenoids that are bad in the trans.......the #2 shift solenoid and the Duty C. It shifts weird from 2nd to 3rd gear and also has torque bind. When I put the FWD fuse in, the torque bind goes away. Even if it's not the Duty C, I'm changing it anyway. Sooner or later it will fail. I already replaced the Duty C on my other daughter's 97 Impreza, so it's not a big deal. I have a full pit in my garage, so it only takes me about 3 hours to do the job.

As far as my being suspect of the #2 shift solenoid being bad, there's a significant delay when it shifts from 2nd to 3rd. Initially it shifts like normal, but then after about 2-5 seconds, you can feel it actually grab. I don't suspect a torque converter issue, as it has no issues in any other gear. If the # 2 shift solenoid doesn't fix the shifting issue from 2nd to 3rd, it's not that big of a deal, since I was going to drop the pan anyway.

[mjm4jc]

I'll try the procedure again to pull the TCU codes. Hopefully, that will confirm what I already suspect.

[wtdash]

+1
Sounds like you have it under control, but have you done the ATF refresh with 3x Drain>Refill>Drive ? I've done that on a couple '90s 4EATs and after doing the ATF refresh and then go drive in figure 8's the TB actually got better.

But yeah, if the FWD fuse eliminates the TB, it's NOT the Duty C and it's in the clutch pack /plates, which can also be fixed when you replace the Duty C. The USMB site or others have the procedure. I did it years ago on a '90 4EAT.

RE: The 2nd>3rd gear issue, I believe their is a Band Adjustment that can be done, but don't know if it'll help. See this: https://jdmfsm.info/Auto/Japan/Subar...Files/4EAT.pdf

[mjm4jc]

I've done the drain & fill 3X's twice, plus another 2 drain & fills in the last 80K. The trans fluid is so fresh/clean/clear that it's hard to see on the dipstick, lol.

I do think that there may be something to doing those figure 8's. I will give that a try.

FWD fuse----funny thing with this is that if I remember from my hours of reading (years ago and recently) I thought that there were some people who had TB that went away with the FWD fuse in but still resulting in a bad Duty C? I could be wrong here. But if it's not the Duty C causing the TB, wouldn't it only leave the TCU and clutch plates as the culprit? And with the 16 flashes, I'm assuming that the TCU is working properly? But then again, I have also read where people had good TCU's except for the one circuit that controls the Duty C.

I'm thinking more about the TB now as I'm typing. With our old 97, the TB was just a stiffening of the car when making sharp turns from a stop or at really low speeds. This car does that same, but it's more of a shaking/shuttering when turning. What exactly happens to the clutch plates that causes the binding (other than the fact that their burnt up)? The car sat for several months before this started. Not sure if that has anything to do with it?

[wtdash]

Maybe the FWD fuse didn't eliminate the Duty C being bad, but my understanding that if the FWD fuse got rid of TB the 'electronics' (Duty C) were working; if not the Duty C had died.

Most of my Duty C and TB info is from older posts on the USMB, so suggest you try their search function (not the best). Here's a good one: https://www.ultimatesubaru.org/forum...problem-fixed/

IIRC, I used a file or other tool to grind down the grooves on the ''clutch gear' in that pic comparing the two.

But if that Impreza had been sitting, I'd definitely do those 8's.

Also, swapping the TCU isn't tough - finding one might. I can't recall if the Impreza and Legacy and earlier models shared the same TCU plug connector. Ebait might have pics to compare, or your local PullNSave, etc. may be the best bet.

[mjm4jc]

Hello everyone,
Just want to give an update here. So the original problem was the 16 flashes at start up coupled with torque bind and major shuddering/shaking when pulling out from a stop (even going straight) and when slowly going around turns.

So the shuddering/shaking problem was due to a broken u-joint on the drive shaft where it comes out of the trans. The center and rear joints were good. But the front was so bad that it was about ready to come completely apart. The new driveshaft fixed that.

But I ended up taking the tail end off the tranny and replacing the duty C, since I still had torque bind after replacing the driveshaft. Unfortunately, after replacing it, I still have it. It's not horrible though. But if I'm trying to park and have the wheel cut all the way to one side, it is definitely stiff. I can hear an occasional skidding in the rear wheel/wheels.

Now I know from my daughter's other Subaru that we no longer have (97 Impreza L) when she had this issue, the replacement of the Duty C fixed it completely. So either I have different issue, or the new solenoid that I put in is bad. The solenoid was a genuine Subaru solenoid. Could also be a TCU issue I suppose. I also know that from the other Subaru that I fixed, when the duty C was bad, it was far better in the snow........(I know some of you are going to raise eyebrows and arguing with me on this). But really, when I fixed her duty C the car wasn't as good in the snow especially going up the steep hills.

This leaves me to my next question, which may also raise eyebrows, lol! Since I am not willing to take the tail end of the tranny off again, nor do I have the time to troubleshoot the TCU, wouldn't it be best from me to figure out how to install a switch inside that car that is wired to the FWD fuse on firewall, so she can drive it FWD but flip the switch to have AWD when needed?

Please advise

[wtdash]

Sounds like it's either the TCU or the rear clutch pack
- Did you review that USMB Post?
-Did you do the figure 8's with frest ATF?

Yes, you can install a switch - just wire into the FWD fuse or at the TCU pins. Quite a few did that to 'save fuel' - not sure that was the case, but it was a workaround for the TB.

And yes, the AWD works better 'cuz you basically have full-time/FT AWD/4WD. There's also a switch 'hack' for that on the web - if you ground a pin on the TCU it'll engage FT4wd.

[mjm4jc]

WTDASH----First, thank you for the post you made a few weeks ago that I didn't get a chance to reply to. Your insight is helpful.

I did check out the link you posted on the USMB site. It was a bit confusing. One thing that guy said in that thread, which was why I didn't probe any further, was that when the FWD fuse was in, he still had TB. This was not the case with mine. Putting the FWD fuse in eliminated all TB. Unless I'm mis-interpreting what he said..............."With driveshaft in car and FWD fuse in box, when taking right or lefts the rear wheels lock up and make the whole car shake......" ?????????

I did do the figure 8's but not since I drained and filled with new fluid yesterday. I guess that's something I can do today.

After I finished the Duty C replacement, I disconnected the battery for a few minutes then tied the cables together to discharge everything. On the first start after doing that, I did not get the 16 flashes. But after shutting it off and starting up again, the 16 flashes came back.

There's one thing that may be worth noting, but not sure if it has anything to do with it. When I put the VIN in on the Subaru parts website there are two duty C solenoids that come up for 1995 LX Wagon 2.2L. But one is like 100.00 more than the other. When I called the dealers, (yes 2 of them) I got mixed answers. One dealer said that either one was suitable, and the other dealer said there's only one that's for my car----the more expensive one. Anyway, I bought the cheaper one, and it looked exactly like the one I removed. Don't know why the two different part numbers for the same solenoid.

[wtdash]

One issue, is "If the FWD fuse works, the Duty C is working, too, then why does the TCU have the 16 flashes?"

From reviewing this post thread, it was never determined what the TCU codes were, so you don't really know if the Duty C was causing the code - or if was the shift solenoid you mentioned, or some other undiagnosed issue. If you can't get the TCU codes to show then maybe a different TCU would help?

If there is confusion about the FWD fuse's function:
"....if the FWD fuse eliminates the TB, it's NOT the Duty C and it's in the clutch pack /plates <transfer clutch>, which can also be fixed when you replace the Duty C. "

Said another way, TB + FWD fuse = bad duty C (the duty C is not disabling AWD). Issue is likely electrical.
No TB +FWD fuse = functional duty C (Duty is disabling AWD)>>Issue is likely mechanical - the tranfer clutch is binding.

>>> Did you inspect the tranfer clutch when you had it apart?>>>

No offense - but based on your explanation before you replaced the Duty C, "Putting the FWD fuse in eliminated all TB." Means, the Duty C is not your issue - it's mechanical and either you can fix the transfer clutch, or install the FWD switch.

The 16 flashes after a 2nd start is common in my experience. Most codes don't show up until after a few drive cycles/engine starts, as the system seems to double-check issues before throwing a code.

I checked the Subaru site, too. Confusing to know which of those Duty C's to buy- the dealer should be able to determine it based on VIN, but being almost 30 years old maybe not so easy?

[mjm4jc]

Good stuff here, thanks!
Yeah, without knowing the TCU codes I was basically going of of memory and experience with my decision to replace the Duty C. With our other 97 Impreza, the duty C fixed the torque bind. What I may not be correct about (going off memory) is whether or not the FWD fuse eliminated the TB or not. I thought it did.

On this Impreza, however, the FWD fuse did alleviate the TB. Although I did feel some slight TB with the fuse in but only going in circles with the wheel turned all the way. I guess any AWD vehicle may show some stiffness under those circumstances. But with the FWD fuse out, doing the figure 8's and going around in circles was terribly stiff, and the rear wheels hopped and skidded a lot.

Transfer Clutch---I guess I was so certain that the new Duty C was going to solve the problem that I didn't inspect the transfer clutch itself. Of course now I can kick myself for not doing so.

Duty C solenoid---So if I did buy the wrong solenoid, even though it's listed for that year, shouldn't it still work the same?

I probably will move forward with the switch. I did read somewhere that driving the car in FWD mode can cause damage???........but I don't see how that's possible. I think the car should be fine in FWD and using AWD in a 50/50 split only when needed or on a temporary basis shouldn't hurt anything. Aren't manual transmissions 50/50?

I can't believe my scanner can't connect to the TCU on this car. Has anyone been able to pull TCU codes with a regular scanner that they sell at like Autozone, etc? Is it only possible to get these codes from the dealer?

[wtdash]

Yeah..mixed info online about FWD causing damage - I reviewed the OM and it's used for maintenace and when using a temp spare tire. Yeah, MT/5-speed cars are 50/50 - no option for FWD only.

I can't comment on which version of the Duty C should work. But if the FWD fuse is installed and the TB is less, if not completely eliminated, it's working.

I would guess a higher-end scanner or the dealer are the only options to pull the codes, if the DIY TCU code retrieval doesn't work.

[mjm4jc]

Thanks for staying with me on this. I really do appreciate the wisdom. One more thing I was thinking about concerning the FWD. When the fuse is in, shouldn't the FWD light come on in the instrument panel? It does not light up. I just replaced all the bulbs in the entire panel about a month ago. Pretty sure I changed that one too. It didn't light up when the fuse was in on our other Impreza either.

[wtdash]

Yes - 100% that FWD light should be lit w/the fuse in. Probably should light up - like all the other lights do - when the key is first inserted and at the 'accessory/on' position (not start).

Edit: Wasn't on in the other one either? Hmmm. The FWD fuse holder is by the passenger strut tower on the Impreza, correct?


You're welcome - wish there was a clearer path forward.

[mjm4jc]

So I just went out and turned the key on, and the FWD light does not come on. I guess I missed that one when I changed the bulbs.

Something I noticed on the handshake procedure that someone else pointed out on the Subaru Outback forum. Between steps 7 & 8, how do you turn the ignition switch off if it's in 1st gear? I'm assuming off means fully off like when you first put your key in. Correct?

Warm-up the engine.
2) Turn ignition switch to OFF.
3) Turn ignition switch to ON.
4) Start the engine.
5) Drive vehicle at speeds greater than 20 km/h (12 MPH).
6) Stop vehicle.
7) Brake pedal depressed and move select lever to 1 range.
8) Turn ignition switch to OFF.
9) Turn ignition switch to ON.
10) Move select lever 2 range.
11) Move select lever 1 range.
12) Move select lever 2 range.
13) Move select lever 3 range.
14) Move select lever D range.

The link below is from a guy who designed a circuit board to switch between FWD and AWD at the flip of a switch. But isn't this the same thing as what I said about splicing into the FWD fuse with a switch, or am I missing something?

https://www.rs25.com/threads/4eat-di...&sortby=oldest