Hoping someone out there has come across this problem. My husband is a Cadillac mechanic in business for 15 years. This one has us STUMPED!!! 1995 Cadillac STS vin "9" engine code. Code PO86 constantly returns. Initially replaced the PCM. Code came back. Began changing parts in Trans. Replaced Transaxle pressure switch, torque converter selonoid, input speed sensor, pressure regulator. Performed Trans service. Vehicle speed sensor not replaced. Finally replaced Trans with remaned trans. Same exact problem, almost immediately. Code 86 comes on and the trans shifts HARD! We replaced the PCM again...this time remaned from the dealership with the newest service #88961146 which replaces original service #16197429. We are positive it is an electrical problem but we do not know what else to try. Any help would be fantastic. Thank you in advance for your time!! P.S.Has only 94K miles and in immaculate condition. One owner serviced properly over the life of the vehicle and trans was clean as a whistle inside. Thank you, thank you!

 

Do you have FSM? Do you know how to use onboard diagnostics?

 

What is FSM? We do know how to use onboard diagnostics. We also have the Snap-On scanner and have been looking this up on AllData.

 

Factory Service Manual. When you run tests for P86 found it alldata where do results take you?

 

PO86 is undefined gear ratio. The trouble tree took us all through the aforementioned transmission parts. We replaced all of those parts and then the transmission. It has nothing to do with the trans being bad so we know its electrical. One thing that is odd...if we change the pcm from the original to another, PO86 comes back alone. If we put the original PCM back, PO86 and PO76 come back together. There is something electrical going on, but with fifteen cars a day going through our shop, we simply don't have time to figure it out. Its driving us nuts!! If you can think of anything at all that could be the correlation, please let us know! Thanks so much for your input and time.
Alissa

 

What did the trans supplier/rebuilder say about it. Did line pressure increase with acceptable range using onboard test? Post P086 snap shot data stored in pcm; unfortunately it will only 1 frame no before or after. VSS could cause it without setting P024 vss, P024 requires different conditions to be met than P086. You could also monitor vss watching for glitch in speed, and check how much play is in right tripot where it goes into trans. if it is sloppy inrupter on output shaft could be moving away from vss,causing code.

 

Thank you so much for your input. The VSS is the ONLY part that we did not replace. It very much could be the problem. Ray did say that both axles are in good condition. We are going to take another look. Thanks so much.

 

Did anyone ever figure this problem out? We have the exact same problem in our shop. Does anyone know how I can get ahold of RayCaddy? Send a message to them? Any help would be great. This is driving us nuts.