Mechanics

CHEVROLET CHEYENNE LIMP MODE PROBLEM

1995 Chevrolet Cheyenne

I get a trouble code 81. Shift solenoid 2-3 open or short in circuit. Here is what has been done. My truck went in to limp mode. Disconnecting battery resets it and I works fine, but never goes past 3 days and it goes in to limp mode again. I took my truck to a transmission shop. My bell housing was broken. I replaced the transmission with a used one. I replaced the internal wire harness and 1-2 and 2-3 shift solenoid. Problem was no resolved. After a few days it went into limp mode trouble code 81. My truck used to turn right on with a few turns of the engine /few cranks. Now it takes several cranks before it starts. What I did notice is that its at start up that my transmission goes straight into limp mode. Disconnecting the battery resets it and once again it works for a few days. In some cases just for a day. I did replace the ECM and the issue continues same trouble code 81. I am thinking it has something to do with engine timing, engine ignition coil, maybe even the ignition spark module or even fuel delivery issue. This is based on the fact that it is going in to limp mode while starting the truck and not while driving. I have invested $700 in this truck and realy dont want spend any more with out being certain the exact issue. Based on my information what can it be that is causing my issue and what troubleshooting steps do I need to take to solve this problem.
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CECtech1
November 3, 2012.




Did you use the harness in the valve body from the old trans?

Re setting it does nothing for the issue. It is definitely the trans and controls for the trans

Roy


No, I installed new harness. I just find it hard to believe that with a different trans and different ecm I get the exact same trouble code 81 designating there is a problem with 2-3 shift solenoid.
It just does not make sense.


Tiny
CECtech1
Nov 3, 2012.
I agree, but when you buy used parts with no history, this is the chance you take.

Did the trans shop track down the issue form the old one?

Was the harness checked for integrity?

Roy


Shop dropped the tranny cause they could not find anything, they said when the transmission losses pressure it can go into limp mode. Meaning internal damage. After dropping tranny they discovered the bell housing broken. They were going to get a used tranny and replace the internal components with my old one and replace the harness which was in stock. They did not not say which harness. They wanted 1800 or 2500 rebuilt of used tranny. Could not afford it so they charged me 350 for dropping the tranny without reinstalling. I ended up installing a used tranny my self and replaced the valve body harness thinking thats what they were refering to. The truck runs great and it shifts smoothly when I reset the ecm. What got me to question the ignition system is that after aggressively researching my issue a bad electronic ignittion switch and fuel delivery can cause the tranny to go into limp mode. If thats they case that opens a whole lot of possibilities ranging from timming and something going bad in the ignition system. Since everything is electronic, how the engine runs can cause the false information to be sent to ecm. I did replace the ignition switch to eliminate that.
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Tiny
CECtech1
Nov 3, 2012.
No, your heading in the wrong direction. The engine will not cause limp mode.

Roy


This is the wiring diagram. Trace each wire

Roy


O.K. Some of the information on the web can be misleading. Thats why I am getting professional advice. Let me ask you this. How about bad ground. Could bad ground cause it to go in limp mode? My reason for asking is that my ground battery cable was very loose. The bolt is to long and I notices that the ground cable did not tightened firmly to battery. Im still trying to figure out how my truck was turning on. I went ahead and fastened it down. Since the ecm reset will need to drive it to see if it goes into limp mode. Cant say it will fix it? Also If you can could please repost the diagram with a larger one. Its to small and words are not readable. I tryed zooming and it just gets fuzzier. Thx


Tiny
CECtech1
Nov 3, 2012.
Nope, it was not my ground cable. So based on your information this is what I am going to do. Trace the wire for that 2nd - 3rd Solenoid. May just replace the external harness to eliminate the wiring and connection issue to transmission mission, which Could be it. Thats about $40.00. If you know where I can get it cheaper that will be great. The next logical step is to test or replace the ECM. The obd test would not be logical since a bad ecm can give a false diagnostic reading. If there is a way I can check it first, a place I can take it to or send it that wont cost too much, I would like you input on that as well. If not I will have to purchase a new one at the Auto parts. They have it for about $100.00. Lastly the transmission. I still have a few months of warranty left on it. Not really looking forward to removing the tranny again. Its an old truck and really dont want to invest much more into it. If you have any recommendations let me know thx


Tiny
CECtech1
Nov 4, 2012.
Oh I almost forgot! Just one last question before I start searching wiring issues. The Big Switch that is installed on the transmission lever. If that is faulty would it cause it to go int limp mode? It is part of the transmission wiring along with the speed sensors? Thx


Tiny
CECtech1
Nov 4, 2012.

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