transmission issue

[gordy3683]

I figure id ask here before going to a trans shop and possibly getting lied to.

Ok so my truck (93 k2500) doesnt shift into overdrive all the time. It shifts fine into every other gear and doesn't slip at all but shifts into overdrive only when in it feels like it, so any thoughts? Might the trans or at least overdrive be shot?

 

[colbythekid]

Maybe one of the solenoids is going out. I am not 100% but I think that there are two, one for two - three shift and one for the three four shift.

Colby

 

[WarWagon]

Use a paper clip and read the codes from the "Service Transmission Soon" light. The transmission codes do not turn on the SES light that I have ever seen... Drop out overdrive yes, turn on light, no - it isn't an emissions problem and the 1993 computer has nothing to do with emissions.

Then you have suspect wiring. Check the speed sensor wires, two separate 2 wire plugs off the transmission, front and back of trans, for falling apart and shorting out.

Next you will need to check TPS voltage. ~0.5v or more at idle. Less and it will trip a code 22.

Last, would be the main transmission plug checking for oil or backed out pins.

Then and only then suspect transmission issues like a bad OD sprag. This would have ratio error codes stored in the computer.

 

[THEFERMANATOR]

TPS is the normal culprit for loss of OD, or a temp sensor making it think the trans is cold or the engine.

 

[NVW]

Is it possible it's shifting into all 4 gears but the TCC isn't locking? A temp sensor like Ferm said would do this.

 

[plstokes]

I would look at the solenoids. My BIL bought a Saturn from a guy for $250 because it wouldn't shift past 2nd, ended up being the solenoids. He was actually joking with the guy and said "I'll give ya $250 for it" and he took him up on it.

 

[THEFERMANATOR]

I would look at the solenoids. My BIL bought a Saturn from a guy for $250 because it wouldn't shift past 2nd, ended up being the solenoids. He was actually joking with the guy and said "I'll give ya $250 for it" and he took him up on it.

Theres only 2 shift solonoids in a 4L60E or 4L80E trans, so a failed shift solonoid will normally result in a loss of all gears as the PCM will go into limp mode or it will only have 2 gears is how I've normally seen them fail. It could be a solonoid, but no 4th gear is normally a sign that the PCM is seeing too much throttle(TPS failed) or thinks the trans is too cold and is locking it out to heat the engine and protect the trans. STart with the simple common stuff first as no 4th gear is a fairly common complaint on the mechanically injected engines when the TPS is going out. It should be fairly easy to hook a volt meter in and monitor the TPS while your driving to see what it is sending out, or better yet see if you can borrow a scanner to see what the PCM is actually seeing(I hate throwing parts at a problem, I REALLY prefer to diagnose and repair which costs less in the long run normally).

 

[bk95td]

It needs to be connected to a scan tool.It may be losing the throttle signal ,engine rpm signal, trans input signal , trans temp signal[internal trans sensor]trans output signal or 4wd low range signal. Only guessing without the scan tool. I had a bad pcm that would make me loose OD and lock-up intermitantly. You can't see that happening without a scan tool connected on a test drive. All the 93s and the 92 in my sig have had the pcm replaced.High failure rate?

 

[docdray]

simple issues are corroded/loose/dirty wiring plug on tranny, deteriorated wiring in pan, loss of ground. send me pm if you want pinout diagram better clarity with email. temp switch affects rpm, tcc apply.
will have 12v @ tranny, ecm switches grnd