Need help troubleshooting my trans. :(

[93ParkAvenue]

I'm having some issues with my trans and would like to attempt to solve without taking to a garage. I am fairly uninformed about auto transmissions as everything else I own is standard so please bear with me.

Just bought the car(93 park avenue) a month ago. 120k miles on it. Was told it had a new trans installed prior to the previous owner getting it(around feb 2012). That's what they told her, but I can look at it and tell that was a lie. Not only is it as dirty as the rest of the engine bay, but the trans mount was busted. Who puts a new trans, or even rebuilds a transmission, and doesn't at least put a 30 dollar mount in? Moving on..

This is what is happening. I pulled codes last night. 23(iat reading too low), 39, TCC circuit, 58 security system, 65 cruise servo position sensor.

If I start the car from cold, place gear selector in Overdrive, and drive, the car will drive fine for about a mile or 2. After that mile, the car will then downshift back to 3rd.

If I start the car from cold, place gear selector in Drive, and drive, the car will drive fine, but obviously, only stay in 3rd. After a few miles, I can shift up to Overdrive and it will go to 4th. Shortly afterward(usually less than a 1/4 mile), it will downshift and stay in 3rd. I cannot make it go back into 4th by using the lever.

In both cases, I am able to switch the car off, and restart. It will go through the gears and shift to O/D, or if I did it coasting in neutral, will go into 4th. It will not remain in O/D however and will go back to 3rd.

A new problem surfaced a few days ago. While driving with the gear selector in O/D, the car slipped from 1st to 2nd. It would hold 1st for way too long, slip as if it was in neutral, and then grab 2nd. The 2-3 shift was fine. However, it did not do this when the gear selector was in 3rd. It has only slipped 3 times that one day, so I am not sure the gear selector isn't a coincidence.

I've checked fluid and it is clean and clear, no off smells, and is the right level. I don't have many tools other than your standard ratchets and wrenches. I do have a multimeter. Researching online turned up some leads on the trans temp sensor, but I'm not sure if mine has one. The 1-2 shift seems harder than I would expect out of this car, but I have prior experience with park avenues so I'm only guessing. It seems to be temp related but again, I'm not working with any evidence other than symptoms.

Thanks for any info. I'll be cruising in 3rd in the meantime.

[robertisaar]

sounds like there's too much slip when in 4th gear, which is causing the PCM to default to 3rd instead. actually a fairly common issue with 4T60Es.

it's not the greatest idea, but you can temporarily disable the TCC PWM circuit and that MAY fix your issue at the consequence of making TCC apply rougher.

the three other causes i've seen for this before are the trans temp sensor acting up(which yours does not have), slip in the driveline(either the TCC itself or the clutches for 4th gear), or a valvebody issue that allows fluid to be vented, causing slip.

[93ParkAvenue]

Thanks for the reply. I drove it today stop and go for 5 hours(mail delivery). I kept it in 3rd and it never slipped.

I tried upshifting manually, and it always went to 4th. Before it would kick back down, I put it in 3rd and tried a minute later. It always goes back to 4th, unless you leave it in 4th and it downshifts. Then you have to restart.

What would be the reasoning behind temporarily disabling the TCC PWM circuit? And there is some yellow writing on the transmission(like you would see on a junkyard part) so I assume it was replaced, not a new one installed like the previous owner was told. I may do a fluid change in case the knuckleheads added the wrong fluid. Are there any additives that are recommended or are they all snake oil?

[robertisaar]

sometimes, the TCC PWM solenoid is the culprit as to why it slips enough to have the PCM disable 4th gear. if that does fix the problem, you would need to either pull the sidepan and replace the solenoid or replace the transmission altogether. from the way it's acting(needing to key off), it's definitely the PCM disabling 4th gear on purpose. it may or may not be disabling TCC lock as well.

if you deliver mail with it often, i'd recommend an external trans cooler, low speeds(especially with constant speed up and slow down) heat up the trans fluid really quickly.

i don't use additives, since they mask a problem(if they do anything at all) rather than fix it.

[93ParkAvenue]

New Problem! Yay!!!

Was on the route yesterday. Got to a mailbox and tried to advance to next box. Car lost first. So I'm now down to 2 gears(2 and 3). A little farther, and my car overheats. I let it cool and check the fans as I'm waiting by turning the key to on, and turning on the a/c. Worked in my camaro so I figured it would work in the buick. No dice. I drove it to see if the temp would drop while it was moving and it did which supported my no fan test.

I checked fuses and sure enough, there is a 10 amp cooling fan/transmission fuse. What in the world does it control in the trans? Did some component in the trans kick the bucket, causing the fuse to blow? I disconnected the battery in the hopes of clearing codes and will replace the fuse. Then a short test drive to set any codes again and will report back.

[robertisaar]

got an exact location of the fuse? i can probably pull the diagram and see what all it powers, if we can figure which fuse it is.

[93ParkAvenue]

I believe it was fuse 16. I'll double check.

16 it is. "cooling fan/transmission".

[robertisaar]

fuse 16 powers:

low speed coolant fan relay
high speed coolant fan relay
TCC/ABS brake switch

it also powers anything inside the transmission that uses 12 volts(shift solenoids, TCC). pop the fuse and then the lowest gear you can select is 2nd gear.

[93ParkAvenue]

Based on that fuse blowing, and the problems I mentioned beforehand, are you leaning toward something electrical being the cause of my trans gremlins?

I'll look around for a trans electrical diagram later to see how I would go about disabling the tcc pwm circuit.

[93ParkAvenue]

Reconnected battery, replaced fuse and drove for 10 minutes. Did just like it was supposed to. I checked for codes afterward and there were none, but I'm sure I will throw some codes saturday, possibly blow that fuse again.

I did search around a little bit for the correct way to disable the tcc circuit. It looks like all you do is clip a wire. However, I am unsure of the wire and I didn't stumble upon a diagram.

Thanks for your help and time.

[robertisaar]

looks to be a dark blue wire, in position B.

as opposed to clipping, you could de-pin it, though it's not as simple as it sounds.

http://i.imgur.com/5O5VI.png

[93ParkAvenue]

I surely don't want it to throw a code, but I know it will. Just drove it again for about 20 minutes to my parent's house, then 20 minutes back. No problems. Even had overdrive.

That's ok, Saturday it will probably overheat on me again....Got extra fuses in case. Hopefully the trans cooler will be in by Friday.

[robertisaar]

what changed? just replacing the fuse? or did you clip the wire as well?

[93ParkAvenue]

All I did was replace the fuse. I don't know if getting super hot(the engine actually overheated) did something or what but it hasn't gone this far without acting up.

I am going to check my grounds when I get a chance. The alternator also isn't charging fully. Battery test said 89%(guy from autozone with tester). Also said something about a diode in the alt was bad. I wonder if that is causing some of my issues. Sorry I didn't mention it before.

[robertisaar]

i wonder if the fuse was just the weakest link and had been for however long you've been having the issues.

the TCC PWM solenoid normally draws either 1 or 2 amps when fully on, it's been too long since i've looked into it to be sure. perhaps that load was tipping the fuse over the edge without causing it to pop.