4L80E in a 1997 Chevy van limp mode


  #1  
Old 11-06-21, 12:51 AM
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4L80E in a 1997 Chevy van limp mode

Hi guys,
I have a 1997 Chevy van with a newly rebuilt 4L80E gearbox. It works through all gears but gearshifts are very harsh, almost banging in the next gear. And, when been driven up to working temp and engine turned off, when starting again the gearbox goes into limp mode, only reverse and second gear working.
If diconnecting the battery for about 10 minutes the problem goes away and I can drive hours if I do not turn of and off the engine. So I guess that the computer detects a problem in the gearbox, temp or mayby pressure and when turned off goes into the limp mode. Bcs, if going to limp mode while driving could really hurt the gearbox/Engine system.

Any ideas of where to start the search for the problem ?
I have connected a OBD-II scanner, but it detects no trouble codes, and with the simple OBD-II scanner I have I can not goes into any gearbox readings.

Help would be much appreciated !
Best from Bo in Sweden
xx@xxxx.xxx
 

Last edited by Pilot Dane; 11-06-21 at 03:36 AM. Reason: removed email address
  #2  
Old 11-06-21, 05:16 AM
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In the USA, many auto parts stores will read any OBD codes for free. If Sweden doesn't have this, suggest buying a code reader that reads auto transmission codes.
 
  #3  
Old 11-06-21, 06:02 AM
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For slamming into gears, might try an input speed sensor. I've had them fail on my wrecker (also 4L80E) and that is the symptom. You can even swap the input and output sensors as a troubleshooting step (they're the same), but of course if they were both to be bad, you wouldn't see any difference. I've also in the past had similar problems that you are experiencing. In addition, I had a failure mode where I would lose overdrive/high gear. Only thing I can remember (because I haven't had any of the issues in many years) was that at one time, at least, it was a wiring harness issue. I will try to chat up my favorite tranny guy next week and maybe get some more insight. I also think I have a packet of info on 4L80E issues stuck in the truck somewhere. I'll try to dig it out later. As Bob suggests, a full scan that will show tranny codes would be a big help. If you can get codes, I have a factory manual for the truck that has an extensive section on tranny codes I can consult.

I CAN tell you that none of the problems I had was ever the actual computer; truck still has OEM unit installed.

 
  #4  
Old 11-06-21, 10:55 AM
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The scanner is a good idea. You want one that has live data so you can see your trans temp, and you may also be able to check solenoids and sensors.
Make sure that your tranny fluid level is at full mark, and that it is light to medium red vice dark red. The fluid should not have a burnt smell.
Have you discussed this problem with the company that sold you the transmission?
 
  #5  
Old 11-08-21, 12:46 AM
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Thanks All for your kind answers.
I have a simple OBD-II reader but, can not see the tranny codes in that one.
This week I will go to a US car repair shop here nearby Nybro, Sweden.
He is not sure if his computer can reach down to the tranny, but, lets hope.

As for speed sensor when harsh gear change, it still changes gear in the right speed, depending on load and revs etc, compared to the other vans I have had.

But a 1997 4L80E electrical diagram would be great help.
Anywher to download, or , can one of you guys help to email it with OBD-II codes to [no emails in posts, please]

Best //Bo
 

Last edited by the_tow_guy; 11-08-21 at 03:20 PM.
  #6  
Old 11-08-21, 03:21 PM
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Was really busy today, will try to pick brain of my tranny guy tomorrow. I'll see what my manual has for schematics.
 
  #7  
Old 11-09-21, 07:11 AM
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Okay, chatted up my tranny guy this morning. He basically said you really need to get some codes. Dug out some old troubleshooting papers; a couple of the items do refer to wiring issues for similar symptoms. The tranny section in the shop manual for my truck is over 100 pages and there are multiple schematics. Too much to scan and send. Best once you get codes for me to give you just what's relevant.
 
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Old 11-09-21, 07:22 AM
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Here's the short version on the old papers, just the items that closely resemble your issue:

COMPLAINT: Goes to fail safe when hot or going over bump.
CAUSE: Wires or bad ground. Look for codes.
SOLUTION: Check ground strap, replace shift solenoids, then wires if necessary.

COMPLAINT: Goes to fail safe with codes 73-81-82-82
CAUSE: Ignition switch. Does not connect computer.
Comment: Restart and turn switch backwards slightly. [Side note: I have NO idea what this means exactly ]

Shift Solenoid complaints:

Solenoid "A" complaints: Starts in 2nd. No 4th [May have code 82]
Solenoid "B" complaints: [May have code 81 and also 68]
Starts in 3rd, bindup in "1". Fail safe mode. 2nd only. Might be okay cold. Falls out of 4th - no 4th when warm - No 3rd or 4th - No lockup. 2-3 slide or cutloose feel at hard throttle [light throttle okay]. These complaints can also be caused by defective wire harness

Code 81 0r 82 indicates solenoid or connections to the solenoid(s).
 
 

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