Jump to content
CaddyInfo Cadillac Forum

99 Deville no fourth gear-help!


Recommended Posts

hello, first timer here. I recently bought a 99 deville. the car will not shift into fourth gear. it stays in third up to the 90 mph that I have had it. just like it doesnt even attempt to shift to fourth gear! I have checked all of the fuses, front and back, replaced shift solenoids and valve body, and fourth gear servo and piston. The couple of times that I have been in the tranny I have I have replaced the fluid with valvoline maxlife. I have cleaned and greased all connectors and grounds I have come across. I have changed AF,FF, cleaned throttle body MAF, replaced plugs, wires, coils ans ign cont module. Dont know if it helps but when I manually downshift to second, it "free wheels". I'm lost. Thanks for your help!

Link to comment
Share on other sites


It could be the fourth gear servo piston seal. Are there any codes stored in the onboard diagnostics?

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

Link to comment
Share on other sites

yes, sorry, the only code is IPC U1255 class 2 comms failure. I changed the fourth servo piston pin, both seals, etc... my shift solenoid elec connectors were melted!

If the servo piston ring (seal) is damaged or cut, it won't go into 4th gear. If the solenoid connectors were melted, that's probably the reason it won't go into fourth gear.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

Link to comment
Share on other sites

well I have replaced the whole valve body, incl solenoids, from a junkyard. and also replaced the whole fourth servo piston pin and gaskets assy. Both were from a junkyard donor and both looked a lot better than mine! Still no change, only code is IPC U1255- class 2 comms. It's making me crazy, and my back surgery is this wednesday. I was hoping to get this figured out before surgery because it will be a loooong time before I will be able to do any more diagnosing! Thank You guys for all of your help!

Link to comment
Share on other sites

Several years ago, we had the translation posted on here from the shop manual. If someone can find it, and post it will be so helpful for many trans issues.

If you put your car in diagnostic mode, the hvac Display will indicate the functions of the transmission. For example when you step on the brake pedal, an image will illuminate on the display, as well as for each gear change there will be an indication of all functions of the trans as it shifts as well as inputs.

If I recall, it was an image of the hvac screen with the translation for each icon.

Link to comment
Share on other sites

well I have replaced the whole valve body, incl solenoids, from a junkyard. and also replaced the whole fourth servo piston pin and gaskets assy. Both were from a junkyard donor and both looked a lot better than mine! Still no change, only code is IPC U1255- class 2 comms. It's making me crazy, and my back surgery is this wednesday. I was hoping to get this figured out before surgery because it will be a loooong time before I will be able to do any more diagnosing! Thank You guys for all of your help!

I would suggest taking the car to a good transmission shop for diagnosis. Most will diagnose the issue at no charge. With a proper diagnosis, you will then know exactly what needs to be done.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

Link to comment
Share on other sites

Thanks guys. Yes I would like to see the transmission sect, if somebody could help point me in the right direction! I really like this car, it's my first Caddy. However I only paid $1350 for it! Supposedly, the engine was rebuilt by a major company here in St Louis and only has 40k mi on it. Tranny and car has 153k on it. decisions, decisions...

Link to comment
Share on other sites

Unless the U1255 is HISTORY and does not come back very soon if you clear it, I would look to fix that too.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...