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

[Fairtax4me]

Not a fluid issue. Electrical problem of some sort. Either the harness plug for the trans isn't connected all the way, or possibly a bad ground for the trans case. Or the TCU has had it. Check plugs and grounds first. Maybe swap the TCU if you can get one for a decent price.

[wtdash]

HI and Welcome to the USMB.

 

And....What was the old trans doing that required its replacement?

 

GL,

TD

[presslab]

Sounds to me like your TCU is locking up/rebooting.  Check power to the TCU, grounds, loose fuses, connectors, etc.  Could just be a bad TCU.

 

The speed sensor codes are probably because you don't have the right TCU.  Tire size is irrelevant, the TCU doesn't know or care what these are as long as they're all the same.  The TCU requires the ratio of the speedometer gear and the final drive to be the same.  If they are close, there won't be codes but AWD will be adversely affected.

[danaroypatton]

Thanks guys.  I'll clean some connectors and check voltage at the TCU this week, then let you know what I find.

[danaroypatton]

HI and Welcome to the USMB.

 

And....What was the old trans doing that required its replacement?

 

GL,

TD

I bought the car without a transmission.

[tirod]

The electrical gremlin would include the dropping resistor connection on the passeger fenderwell, and the wiring loom as the solenoid connections inside the trans hanging down from the valve body. Because it is intermittent, it indicates that heat may also be a cause. As a part warms up to a critical temperature, expansion causes it to separate at a crack and you lose connection, throwing the TC into limp mode. 

 

It would eventually be prudent to pull the pan (save and reuse the fluid) to check the solenoids and wiring inside. The pan at the magnet is in extremely close proximity to the line pressure solenoid next to the drain plug. It it gets pressured up from the transmission jack, it could crack, or simply getting high centered on rough ground off road. If the magnet/pan is resting on it, as it warms and cools it could be causing it to change. 

 

Kind of off the wall, but all the symptoms present to electrical and loss of the circuit as if a solenoid is shorting out. 

 

PS use a gasket, not RTV, as it can dissolve and clog the valve body. 

[wtdash]

You can use a TCU from any '90-'98 Legacy, I believe, as they appear to use the same 3 connectors.

Td

[danaroypatton]

At Josh's advice, I checked input voltage at the TCU. Here's what I found:

 

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.

 

The above voltages are present both when the transmission is shifting normally and when it enters failsafe mode. I read no change whatsoever in either scenario.

 

Thanks,

Dana

Edited February 27, 2014 by danaroypatton

[danaroypatton]

Is there a transistor somewhere? I don't understand that voltage.

[stirnex]

I had a similar problem on my 98 outback.  I thought the transmission was doomed.   The intermittent symptoms defeated several ace mechanics, but we finally found the problem...the sensor wiring harness connector, located below and behind the air intake cleaner.  The fix is to use contact cleaner/lube available at Radio Shack.  Not the spray can, but a small tube of goop that contains stuff to clear out oxidation and to leave behind a seal that prevents future oxidation.  I had this problem for a couple of years, but since using this, have been completely free of this trouble.   All you need to do is separate the connector, apply the goop, and work the connector off and on repeatedly to clean the contacts, then plug in and forget it.   

This same connector corrosion problem could be at the root of many mysterious troubles, as ALL the sensors are wired through it.

Now, if I can just find the reason my AT temp light flashes 16 times every startup.....

[Kharl]

HI!

i am having a similar problem

but mine is stuck in 3rd!

 

it has new fluid, new filter

the test I have done:

all the transmission sensor and solenoids are perfect (I followed the manual procedure for testing and they are all within the range (measuring the resistances in the transmission conector)

 

but the throttle position is bad,

-the resistance between pin 2 and 3 was 8.8 instead 12

-the resistance between pin 2 and 4, fully open, was 0 - 1.7 instead 3-5

-the resistance between pin 2 and 4, fully closed was 8.8 instead 10-12

 

and I haven't been able to test the TCU connectors, I did pull out the TCU and I open it and everything inside looks pretty fine, no burn smell no blown chip

 

can the TPS put the transmission in failsafemode?

 

I want to do the test tot he TCU connector but I don't know what is what I have to do, I have to measure the voltage of the TCU connector (female ones) or the harness connector (the male ones) (I don't know which voltage I would meter to the TCU connectors if I remove the connector to accss the pin.... duh..) but is what I have to do to measure the voltage with the connectors in ints place (in the TCU, and to touch it wth the multimeter's probes in the back side of the harness? while connected to the TCU?

 

sorry maybe bad written sentences due my little english

 

any help will be HIGHTLY appreciated since I am in a remote area, and I use that car for moving my grandma who is very old and that's the only we have for that purpose thanks to its frameless windows (already gone in latest models, very bad from subi)

[Kharl]

problem solved, TCM bad