• The site migration is complete! Hopefully everything transferred properly from the multiple decades old software we were using before. If you notice any issues please let me know, thanks! Also, I'm still working on things like chatbox, etc so hopefully those will be working in the next week or two.

URGENT! Hard Shifting and Transmission Whine!!!

L

lvin4jc

New member
Hello, My name is Joe and I hate that this is my first post on here, but it's a bad one. My 1999 Grand Prix SE with the 3800 Series II engine and I don't know what transmission (automatic) has 157k on it. The engine runs great, but the transmission is having major problems.

Whenever I go over a bump or pothole, my transmission shifts extremely hard on every shift all the way through the gears, just now I was out for a drive and hit a decent, but not very big bump, It shifted incredibly hard and now has that telltale whine whenever it downshifts and has to match with higher RPM's. The hard shifting usually lasts for a good hour or so after I hit the bump, so far if I leave it off for an hour or two and start it back up again it will drive and shift fine until I hit another bump, however, it has never done the whine before so I don't know if it will recover.

Please help me and let me know what I need to do, Thanks for your help in advance :th_thumbsup-wink:
 


Over a bump and it begins to shift hard? Im almost wondering if its electrical? Either that or really bad engine/transmission mounts
 
_nick_ said:
Over a bump and it begins to shift hard? Im almost wondering if its electrical? Either that or really bad engine/transmission mounts
Click to expand...

Well, I had thought about electrical, I just did plugs and wires, but I had considered checking out the coils until the "whine" started yesterday. But sure enough, when I let it sit for a couple of hours and started 'er up again it shifted smooth as glass the rest of the evening.
 
Hard shifts out of the blue like that or over a bump in your case are only going to be caused by the pressure control solenoid and pcm in conjunction with each other and the pcm is seeing a problem so is commanding max line pressure. This will cause harsh shifts and a whine because the pump is working much harder under a max line pressure condition. It is odd that you are experiencing this over a bump but my thoughts are definately wiring or a poor connection between the trans connector on the main engine wiring harness and the trans. You may try to disconnect this connector and plug it back in a few tims and see if anything changes. It is a larger round shaped gray colored connector at the top of the trans bellhousing. Something else that I see time to time is the engine harness having problems because a few wires can rub through. This area is just under your air box and the wire harness will be laying right on some AC lines. If it is and looks like it is running through the wire loom then you should take the loom off and give the wires a close inspection. A good bump can cause enough shake on things that maybe a bare wire to the pressure control solenoid is touching the AC line-a solid ground- and causing the pcm to see a problem and put it in basically a limp mode which gives you max line pressure. Have you checked for any codes with a code reader or scan tool? If you dont have one then most auto parts stores have at least a code reader so you can verify if you have a code stored or not.
 


Trannyman95 said:
Hard shifts out of the blue like that or over a bump in your case are only going to be caused by the pressure control solenoid and pcm in conjunction with each other and the pcm is seeing a problem so is commanding max line pressure. This will cause harsh shifts and a whine because the pump is working much harder under a max line pressure condition. It is odd that you are experiencing this over a bump but my thoughts are definately wiring or a poor connection between the trans connector on the main engine wiring harness and the trans. You may try to disconnect this connector and plug it back in a few tims and see if anything changes. It is a larger round shaped gray colored connector at the top of the trans bellhousing. Something else that I see time to time is the engine harness having problems because a few wires can rub through. This area is just under your air box and the wire harness will be laying right on some AC lines. If it is and looks like it is running through the wire loom then you should take the loom off and give the wires a close inspection. A good bump can cause enough shake on things that maybe a bare wire to the pressure control solenoid is touching the AC line-a solid ground- and causing the pcm to see a problem and put it in basically a limp mode which gives you max line pressure. Have you checked for any codes with a code reader or scan tool? If you dont have one then most auto parts stores have at least a code reader so you can verify if you have a code stored or not.
Click to expand...

That all makes sense, i'll check that connector and the wire loom. I don't have a code reader but I have access to one, I don't have a CEL on, but i'll check for a stored code anyway. Thanks a bunch for the advice, you might have just saved me hundreds.
 
You must log in or register to reply here.
Back
Top