OK guys I am trying to diagnose a problem with a 91 chevy k-2500 silverado pickup. The transmission seems to be slipping pretty bad. Its and automatic 4spd w/overdrive. I pulled the trouble codes out of the computer but the ones I got aren't listed in the Haynes motor manual. I got 65, 75, 85, and 87. These are supposed to be related to the transmission but it doesn't give specifics. If any of you have a better idea of whats going on please help.

Rick

Guncrazy223- My Actron code scanner book says:  65-Large egr failure or fuel injection current low or Right oxygen sensor-rich condition indicated or cruise control position sensor problem.                                         75-Transmission voltage low-possible caused by generator voltage supply circuit or power train control module(pcm). 85-Input or output speed sensors- circuit problems. 87-High gear error- transmission in 1st or 2nd gear when computer commanding 3rd or 4th                         gear.                            

The ECM is only going to pick up on problems that are related to electrically controlled parts, or the sensors that monitor them.
If the trans is actually "slipping" it is more or less going to be a mechanical problem, (burnt clutches, worn out or broken internal seals, ect. ect.)

Is the trans actually "slipping"? (engine revs up, truck does not move, or is slow to move/catch up with the engine rpms..OR engine RPMs "flare" on the shifts meaning the engine races up when the trans shifts)

Or is it shifting late? (as you accellerate the tranny seems to hang in one of the gears too long, then shifts)

Pretty much only certain newer transmissions will actually provide much useful information through an ECM scanner.
Unless yor truck has an overdrive button on the shift knob your transmission is a 700R4 most likely. It has an electrically controlled "lock up" torque converter, other than that it is pretty much a hydraulic sytem.
In order to diagnose yer problem, someone will have to acutally test drive your truck, and (if applicable) a good transmission shop will have diagnostic equipment that is more likely to pick up on transmission related trouble codes.

The problem cant be diagnosed reliably without seeing the truck in person, but here are some things to check:
[b]FLUID[/b]: Is the trans full of fluid? and what color is the fluid? (the fluid should be red, although it can have some brown to it. If it is a very dark shade of brown, or black,...you likely have some clutches burnt.)

[b]SYMPTOMS[/b]: Does the truck slip when it is cold, and then work fine after it warms up? (if so the likely cause is worn or hardened rubber lip seals and O - rings inside the trans which will expand when they get hot causing them to hold pressure,...thus the trans will work when it is warm.) Or does it slip all of the time?
Does it slip in every gear, or only on certain shifts. Or does it slip when taking off from a stop?

At any rate,....if the transmission is acually [b]slipping[/b], unfortunately, it will likely need to be overhauled. (unless it is low on fluid, and you have not driven it far enough to burn it up yet)
If it is just shifting incorrectly,....it [b]MIGHT[/b] need overhauled, or it[b] MIGHT[/b] be an electrical, valve body, or governor problem. Which [b]MIGHT[/b] be able to be repaired without pulling the trans.

I know that all I have told you here is basically "take it to a transmission shop"...but unfortunately that is about the best advise I can give without phisically looking at it, and driving it.

Madmedic:
Professional Firefighter/Paramedic
Gun Collector
[b]FORMER[/b] (thankfully) transmission mechanic
Computer Geek
 [:)]
[i]I thought I should post my qualification since this is the second transmission related question I have answered today in general discussion[/i]
 [:D]

Thanks guys

madmedic

the transmission only slips noticably once the tranny warms up. The fluid and filter are new and at the right level. Once its warm it slips a little changing in low gears but is most noticable at above 30mph. Once it trys for the higher gears it just starts major slipping. The engine revs way up but no acceleration. The transmission in the truck is a 4L80-e, which is a turbo 400 with overdrive and electronic control.

So basically our suspisions are correct that this tranny is coming off and a junk yard unit is replacing it.

Thanks Rick

I'm not a mechanic by trade, but was wondering when GM switched to electronic shift points vs: the old TV cable in their trucks?  If yours has electronic shift, could it be ECM related?   I put a several hundred thousand miles on one R700 I had (with the old TV cable).  I put an aux. cooler on @ about 200K.  Best $100.00 I ever spent on that truck.  Something you might want to consider, when you get rolling again. The tranny ran so much cooler, I could see the difference on the temperature gauge.  Good luck.

guncrazy223,...If your truck has a 4L80E in it, A reputable transmission shop should have a scanner that is capable of pulling trouble codes out of it.....BUT, the symptoms you described are unfortunately not going to be solved without an overhaul. If it is slipping that badly, it is going to have mechanical damage, not just electrical problems. (although it is possible that the electronics initially caused the problem leading to the damage)

By the way, [b]bjklinton[/b] gave an excellent piece of advice for anyone with an automatic transmission:[b]invest in a trans cooler[/b] they ARE worth the money, and heat is the [b]NUMBER 1[/b] enemy of an automatic trans.

I will give another bit of advise for anyone who has an automatic: If it is not working correctly HAVE IT LOOKED AT.....SOON.
Many problems can start as a simple stuck valve, broken/frayed TV cable, stuck governor, electrical problem ([i]not always simple[/i]) ect. ect.....and if left unfixed,...turn into MAJOR DAMMAGE. $$$$$$
And no matter how tempting, do not add any "miracle potions" that claim to fix a worn out transmission, or stop leaks. All they do is swell up all of the rubber lip seals and o-rings so they will hold pressure again ([i]for a while[/i]) making the trans "work" ([i]if your lucky[/i]) ([i]for a while[/i]) And they cause further damage to the transmission. (they pretty much do the same thing that would be accomplished by adding brake fluid)
Additives that improve lubrication (slick 50 type stuff) are absolutely okay though. And certain friction modifiers (help the clutches grab better) are okay in [b]some[/b] transmissions. Check with a transmission mechanic first..........

WHEW,....Ive had too much damn caffeine.