no cel and light works, won't move in drive or 3rd, unless shifted into manually at speed, I have to start by shifting to 1st or 2nd, then once moving can shift to 3rd then drive, drives fine, but no auto shifting at all.

Also, I get a shudder at lower rpm in od, I'm thinking all solenoids are shot

 

Here's a copy/paste from what I posted at ZR2USA when I had similar issues.


Ok, blazer details first.

2002 ZR2 Blazer, 135k, automatic, 3 button transfer case switch. I have searched and read a lot but still have questions.

I got this code yesterday. Cleared it but it returned. I have no issues replacing the solenoid(s) but here's my questions.

Symptoms:
Seems blazer starts off sluggish as in another gear, 2nd - 3rd or so. Can pull shifter into first and pulls off better. Shift into drive and all seems to shift properly as long as I don't come to a stop. I can clear the code while driving and it doesn't return until I stop. Once coming to work this morning I cleared the code while moving and at one stop sign it acted perfectly normal upon take off. Next stop and pulled off, SES light came back on and started off in another higher gear. Only other strange issues I've noticed in the past is that driving down the road, turn off on side street without stopping, giving it gas to proceed, it wants to rev up briefly and then seemed to go in gear and go. It's done that for quite a while. Lately, it seems to have lost some power and wouldn't downshift when pedal was floored as it use to.

1. What parts and brands are you replacing these with?

2. Should I replace all solenoids when inside tranny? If just replacing the bad one, how do you identify them or which one it is? I'd hate to replace wrong one.
2a. What are the GM part numbers if I decide to go this route.
2b. What other solenoids are in there and their GM part numbers? Would you replace these as well?
2c. I will be doing a filter change and all.

3. My tranny fluid was low. Possible fluid leaking into transfer case. I will most likely get GM seals/gaskets for this. Now would this be the transfer case intake shaft seal or the transmission tail shaft seal causing the fluid to overfill transfer case? I haven't checked the fluid level yet but want parts on hand for just in case. I know about the paper gasket. I can return these if not needed.

4. I will check and clean the electrical connections as I've seen posted and recommended in other posts.

5. I have no dash/instrument issues, just this one tranny code and what I described above. Hinting towards bad ignition switch as I've read about. No starting issues or gauge issues. It does have keyless entry.

6. If I get parts from GM, I guess they ill look them up by VIN for correct parts.

7. Filter change fluid capacity?

Thank you!




My fix:


Well it's done. Took my time. A real PITA but not difficult. Had to replace front seal in transfer case. Removed top fill plug and fluid gushed out. I used all OEM GM parts. Also replaced both shift control solenoids while I was in there. I took it as a little bit a insurance. Part numbers listed for future reference. Blazer is now code free. No more P0758. Also had to reset the TCCM since I didn't disconnect the battery. It didn't want to shift to 4 HI or 4 LOW. All ok now. Runs and shifts fine again.

24230297 shift solenoid (S) VALVE A25
14095609 transfer case input seal (S) SEAL A28
15642511 paper gasket between trans and transfer case (S) GASKET H8
24208576 transmission filter kit, gasket and seal (S) FILTER D8

 

Not a shift solenoid issue, if either one is bad you start off in a higher gear than 1st and it shifts once or not at all, but it still pulls.


Your trans needs overhauled. When you shift into manual low the power flow internally is different than when the lever is in the drive or 3 position, bypassing the burnt clutches/broken parts. Once you get it going fast enough that the computer shifts it into a higher gear, putting it back in the drive position returns control to the solenoids and the trans upshifts.

 

So it won't start in 1st if the solenoids are shot? The tranny starts in 1st fine, starts in 2nd fine (doesn't start in first if started in 2nd). Do you feel that it's a broken clutch or something along that lines instead?

 

All a bad shift solenoid(s) can do in this trans is give you the wrong gear, it won't cause it not to pull at all. The only thing that causes that is low fluid level (no pressure to engage things) or burnt or broken pieces inside the trans, requiring an overhaul.

Simplified 4L60E 101:The trans shifts by the computer controlling two solenoids, shift solenoids A and B. In the OD selector position the computer has full shift control of the trans, third selector position it still has full control but OD is locked out. In manual 2 or 1, the valve the selector lever moves redirects the fluid flow inside the valve body, giving you manual control of the trans. It also engages different elements inside the trans, sometimes bypassing the bad one that is normally engaged in OD, giving you movement again.

Stationary, both solenoids are on, giving you first gear when OD is selected. When the computer decides you are moving fast enough for second gear, it shuts off the A solenoid, leaving B on. This causes valves inside the valve body to move, changing what elements inside the trans are activated, and second gear results. Third gear, the computer shuts off B as well, both solenoids off and you get third gear. This is why no power to the trans and you take off in third instead of first. Finally, to get fourth (OD) gear, the trans turns solenoid A back on. 2 solenoids equals 4 possible combinations of on and off, thus 4 different gears.

The solenoids do not control anything like a clutch or band directly, they just control the oil flow inside the valve body and the valves in there are what controls the individual components that give you the different gears. It is possible a valve is stuck, preventing say a clutch from engaging, but most of the time a valve sticks because debris from a self destructing trans part is jammed in it.

So bad shift solenoids can only cause the wrong gear to be engaged, not a neutral condition. From your symptoms the most likely cause is the forward sprag is broken. This requires the trans to be stripped down and rebuilt to fix.

 

I was under the impression that there would be no 3rd or OD gears if the sprag was gone. It goes in for testing today, apparently the tc solenoid is done in too, it shudders at lower 4th speeds and the shudder goes away for a bit when I tap the breaks.

 

TCC shudder is usually caused by a bad converter (which a new one should be included in the rebuild) or the fluid is not the right "slickness" anymore. There are actually 2 TCC solenoids, one is an on-off one in the pump that turns the lockup on and off, and a variable pressure solenoid in the valve body that gradually applies the pressure to the clutch so it engages slowly instead feeling like another shift. The computer also varies this pressure so the TCC is hardly ever fully locked, it is supposed to slip slightly to improve the feel going down the road.

The problem there is the valve the pressure solenoid controls is constantly vibrating back and forth in the bore, wearing it out. The usual symptom is lockup works fine cold but once the trans temp hits about 200, the lockup goes away because fluid is now thin enough to leak around the worn spots. Sonnax makes an updated oversize valve that repairs the valve body, which should be a standard feature of a rebuild but ya never know where a shop may try to cut corners. The other fix is to jam the valve in the full pressure position, this gives the older style full lockup the 700R4 had. Just make sure they use an older style converter with that mod, the variable pressure lockup converter has a carbon clutch that can shatter if a full pressure engagement happens.

The two most likely causes of the no forward are the sprag or the forward clutches are smoked. Sprag is more common.

 

Thanks for the tips. They tested it yesterday and you're right, it's not the solenoids, when they did the tests they noticed that the pressures were not constant. I take it you're a tranny guy eh slim?

 

Going on 17 years now. I'm an R&R guy but also do most of the diagnosing and repairing when it comes to the electronic end of things. Build a few here and there too, mainly manuals 'cause no one else here wants to touch them! .