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I get a trouble code 81

Tiny
CECTECH1
  • MEMBER
  • 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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Saturday, November 3rd, 2012 AT 3:10 AM

17 Replies

Tiny
ASEMASTER6371
  • MECHANIC
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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
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Saturday, November 3rd, 2012 AT 3:45 AM
Tiny
CECTECH1
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  • 12 POSTS
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.
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Saturday, November 3rd, 2012 AT 6:15 AM
Tiny
ASEMASTER6371
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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
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Saturday, November 3rd, 2012 AT 4:33 PM
Tiny
CECTECH1
  • MEMBER
  • 12 POSTS
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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Saturday, November 3rd, 2012 AT 8:34 PM
Tiny
ASEMASTER6371
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No, your heading in the wrong direction. The engine will not cause limp mode.

Roy
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Saturday, November 3rd, 2012 AT 8:38 PM
Tiny
ASEMASTER6371
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This is the wiring diagram. Trace each wire

Roy
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Saturday, November 3rd, 2012 AT 9:04 PM
Tiny
CECTECH1
  • MEMBER
  • 12 POSTS
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
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Saturday, November 3rd, 2012 AT 10:36 PM
Tiny
CECTECH1
  • MEMBER
  • 12 POSTS
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
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Sunday, November 4th, 2012 AT 6:15 PM
Tiny
CECTECH1
  • MEMBER
  • 12 POSTS
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
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Sunday, November 4th, 2012 AT 6:34 PM
Tiny
ASEMASTER6371
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That is the neutral safety switch and has nothing to do with your issue.

Roy
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Wednesday, December 9th, 2020 AT 1:10 AM
Tiny
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Did you respond? I got an email but nothing came through.

Roy
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Wednesday, December 9th, 2020 AT 5:10 AM
Tiny
RODRIGU3Z13
  • MEMBER
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Did you ever figure it out? Mines is having the same issue.
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Monday, October 4th, 2021 AT 9:49 PM
Tiny
ASEMASTER6371
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We never got a response back whether it is fixed or not. That is common when the problem is resolved.

If you could give us your vehicle information and all the information you have, we would be glad to help.

Roy
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Tuesday, October 5th, 2021 AT 2:40 AM
Tiny
RODRIGU3Z13
  • MEMBER
  • 3 POSTS
Sure, I have a 1993 Chevrolet Blazer 5.7. And it does exactly what cectechs was doing. Did a code scan and got codes 12, 66, 73, 81. I had replaced the ecu, and most of every sensor under the hood. When starting the truck, it’ll run fine for about 10 minutes. After that it’ll stay on 1 gear and sounds really accelerated. If I turn off the truck it will work perfectly fine again for another 5-10 then go back to 1 gear only.
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Tuesday, October 5th, 2021 AT 6:20 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

The only codes I see that are related to a transmission issue the 73 and 81. They deal with the transmission pressure control unit and the 2-3 shift circuit. It could be a few different things causing this to set. First, it could be a sensor, internal wiring, or an open circuit between the transmission and PCM. If you look below, I attached the diagnostics related to both codes. Take a look through them and let me know if you are comfortable performing them.

Here is a link you may find helpful when testing wiring.

https://www.2carpros.com/articles/how-to-check-wiring

Let me know what you find or if you have other questions. Also, code 12 shouldn't exist according to the manual. Reconfirm that one. Additionally, other codes and or definitions are related to the ABS.

Take care,

Joe

See pics below.

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Thursday, October 7th, 2021 AT 2:15 PM
Tiny
RODRIGU3Z13
  • MEMBER
  • 3 POSTS
So last night I took a deep dive into this and found my problem. Mind you, I’ve been dealing with this problem for the last year. I found that behind the engine block there was a couple of wires that were melted and making contact causing a short. I had a yellow and black wire shorting out with a white wire and they were both stuck to the block. That fixed my issue but I’m doing that I found that the ground strap from the engine block to the firewall was also torn off. I put tape on those burnt wires for now and took it on a test drive a runs beautifully. I’ll attach a video.
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Thursday, October 7th, 2021 AT 3:42 PM
Tiny
ASEMASTER6371
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Good find.

Thanks for posting the results. It will help a lot of people with the same issue.

Roy
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Thursday, October 7th, 2021 AT 4:04 PM

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