Another 4EAT power indicator post

[danaroypatton]

Hello. Thanks in advance for reading. A bit of a long post, I'm trying to provide as many details as possible.

History
I recently swapped a '95 4EAT (90k) and rear differential into my '92 Legacy L AWD Sedan. The original final drive ratio was 3.90, and is now 4.11. However, the winter tires I am using are significantly larger than the factory tires (I do not have tire clearance issues, BTW). The factory calls for 185/70 14s with a circumference of 76.017 inches, and I'm running 195/75 14s with a circumference of 80.161 inches. At the advice of the local Subaru guru, I did NOT swap the TCU. The steeper gears combined with the taller tires is a near-perfect match IF there were to be a TCU issue:

3.90/4.11 = 0.949
76.017/80.161 = 0.948

I've also verified this by calculating my speed through several mile markers.

Symptoms
1) Intermittent, totally random failsafe mode (stuck in 3rd gear). This can happen at any speed, at any time, and for any duration. It can be downshifting normally as I slow to a stop, only to go into failsafe as I accelerate. I can drive it for 30 minutes on the highway with no problems when it suddenly drops to 3rd and revs. It can happen first thing in the morning when cold, or not. It can be in failsafe for two seconds or fifteen minutes. Totally random. Overall, it seems to fault approximately 25% of the time, and is not getting better or worse.

2) When it exits of failsafe mode, I receive one and only one power light indicator flash. I receive no indications when the 4EAT enters failsafe mode, and I am even sometimes unaware the the transmission has faulted until I observe the one flash. Occasionally, I also get one extremely fast AT temp indicator flash. This happens very quickly. So quickly, in fact, that I can barely even tell which indicator came on. The AT temp indicator may be flashing every time the power indicator flashes, but I don't think this is the case. I cannot tell because when I am able to visualize the indicator, it stays lit for just a split second.

3) Occasionally, but much more infrequently then the symptoms above, I receive the 16 power indicator flashes, indicating a stored TCU code. When I am able to retrieve the codes, I always receive a 32 and a 33 for vehicle speed sensors 1 and 2.

4) As to 3) above, I cannot always retrieve codes. When I follow Josh's code retrieval steps, the power indicator lamp does not always come on in step 3.

Actions
I've changed the fluid twice. It is always bright red with no burnt odor. I've used 1/2 bottle of red LubeGuard each time. I always keep the fluid right on the full mark.

Next
I do not think that I have a mechanical issue with the transmission. The intermittent but binary nature of the symptoms, combined with occasional lack of power indicator at startup point me to an electrical issue.

I could try a '95 TCU, speed sensors, cleaning the transmission connectors, or cleaning and adjusting the throttle position sensor. Any other ideas?

Thanks for the forum, the great write-ups, and the good community attitude. This is my first Subaru and I've had fun learning not only about my car, but what everyone else is doing.

Dana
















Original

[Legacy777]

Hi Dana & welcome to the BBS.

I would agree with you that the problem sounds like an electrical problem. The fact that the power light doesn't always comes on would seem to indicate something is up with the TCU. It is either not getting power or something is screwy with it. Your symptoms kind of fit the transmission just going brain dead....which would be an indicator of the TCU not having power.

My suggestion would be to use a voltmeter or something to monitor the input voltage to the TCU. What you're trying to confirm is that when you do not see the power light come on there is no input voltage to the TCU. If you can confirm this then you have a wiring issue from possibly the fuse box or distribution panel to the TCU. If that is the case, you could always run another set of wires to feed power to the TCU.

That is what I'd suggest doing first....confirm whether the input voltage to the TCU correlates to the power light not coming on.

[Legacy777]

Actually, you could get a small LED light or similar regular bulb at the auto parts store, tee it into the inlet power to the TCU, and then ground the other end of the wire going to the light. This light should come on and stay on when the ignition is in the ON position. If the light doesn't come on or goes out while driving you know power has been cut to the TCU and will likely correlate with your symptoms. Think of it as a reverse warning light.

[danaroypatton]

Thanks for the replies, and great idea with the light. I'll try it this week and let you know what I learn.

Dana

[danaroypatton]

TCU terminals B83/1 and B85/6 are both receiving correct voltage, between 11.5v and 13.8v, when the switch is ON.

TCU terminal B84/14, however, is not. It is supposed to receive 10 to 14 volts when the switch is OFF. It is receiving over 33v with the switch ON. It drops immediately to 5v when the switch is turned OFF, then quickly descends through 4v, 3v, etc., down to 0v within one minute.

So, B84/14 fails the Subaru specs when OFF. I also doubt that the 33v while ON should be occurring, either.

Finally, these voltages are present when both the transmission is shifting normally as well as when it is in failsafe mode. My voltmeter cannot tell the difference between the two.

Thanks,
Dana

[danaroypatton]

I don't understand that voltage unless there is a transistor.

[Legacy777]

Where are you getting your information regarding the TCU terminals? The information I have doesn't indicate any of the TCU connectors on either the 90-94 or 95 TCU are called B83 or B85.

I don't see how the 33 V is correct.....since 12v is the max source voltage. A transformer would be the only way you could step the voltage up. It's possible the signal is a PWM signal and confusing the voltmeter.

Did you try my suggestion regarding monitoring the power feeding to the TCU?

[danaroypatton]

I'm using the service manual, section 3-2a, page 178, and am testing the battery supply and ignition power supply.

Yep, that's what I did. But instead of using a small light, I just spliced in to each of the three wires. I then ran unequal lengths (to keep them from shorting) of jumper wire into the cab and am using my voltmeter.

[Legacy777]

Ok, I'll look through the FSM this evening when I get home.

[danaroypatton]

You bring up a good point about the different TCUs - I just took the advice of local that they're a match. I found the '95 FSM, so I'll compare the pin layouts tonight.

I still don't understand 33v, though. The car does have an old remote start installed, so I guess I'll start tracing that thing around tonight, too.

Much appreciated,
Dana

[Legacy777]

Dana,

Ok, I've got a better understanding of what's going on here and what you're using. You are using the oversea Legacy/Liberty factory manual. The connector names/numbers are different, but the pins for those things you checked are the same. Where are you located? Are you in the US or Canada or are you elsewhere?

Regarding B84 pin 14, that is the backup power supply for the ECU & TCU. That power is supplied by fuse 14. Check and see if fuse 14 is good or not. The ECU & TCU are the only things on that circuit (fuse 14). So you may also want to check that pin on the ECU to see if it is exhibiting the same behavior.

Here is the ECU pin out
http://www.surrealmirage.com/vrg3/ecupins/

Here are the power supply routing diagrams if you need to trace that bogus voltage back to an origin.

http://www.surrealmirage.com/subaru/fil ... uting1.jpg
http://www.surrealmirage.com/subaru/fil ... uting2.jpg

[danaroypatton]

I'm in Alaska. I figured the FSM I am using is American - its written in English. But, I only looked at one. After your last post, I did find a '95 FSM that refers to the connectors as B54, B55, and B56 with identical pin arrangements.

So, on the right track. Fuse 14 was indeed blown. The TCU is now receiving a steady battery voltage through B56/14, but the transmission is unaffected (still intermittent failsafe, no voltage changes w/symptoms, fuse 14 still okay). The three pins I have jumpered are all now receiving correct voltage.

I guess now it's time to start looking at other TCU I/O. I'm going to splice in to the rest of these wires and start going down the list. Again, thanks for your help. I'll repost with voltages.

[danaroypatton]

I guess I've got some more reading to do, as I suspect I'm in a similar predicament as many more before me. I almost cut and spliced every TCU wire today so I could diagnose this thing. Then I figured that's a bad idea. I need to read about the Select Monitor tool or any other ideas of how to read these individual pins without cutting everything. I remember reading some time ago about a physical adapter/software solution, but I don't remember the specifics. Can you point me in the right direction? Thanks.

[Legacy777]

The select monitor is the only tool I know (other than probably some fancy expensive professional scan tool) that will read the TCU.

You shouldn't have to splice or cut any of the wiring. You should be able to back probe the TCU pins. They have little plastic covers that flip up, which will allow you to stick a probe/lead down the backside of the TCU pin. I'm not saying it will be easy and convenient, but you can do it that way.

My suggestion is instead of looking at the TCU, look at the factory manual so you can test the components and wiring. From my experience testing the resistance of sensors and wiring is far more useful. If all that checks out ok, then the only thing left is the TCU....which is pretty much a plug & play effort. The only thing that may be different is if the TCU I/O is different between the first gen & second gen Legacies.