Why would the drivers seat not move forward but still go up or down on a 1998 Cadilac Deville?

Check under the seat for broken wires. Forward and backwards is the function most used and causes the wires to bend back and forth. you may need to remove the seat for inspection or you may be lucky and see the problem just by raising the seat as high as it will go.

I'm not positive about the DeVille, but I've removed seats from lots of other vehicles, and some of that may translate over here.

There should be four bolts (studs, really) going down through the floor from the seat mount frame. You should be able to find the four nuts under the vehicle's floor pan, after you jack up the driver's side and put jack stands under it (if it falls, it WILL crush you to death). Loosen those four nuts but don't remove them.

Now back inside, feel underneath the seat - find all the electrical connectors. Unplug them ALL. Doublecheck, triplecheck, make sure you get them ALL.

NOW you can remove the four nuts underneath the vehicle, tip the seat rearward to verify that you got ALL the electrical connectors, and remove it. It's HEAVY.

something stuck under seat? gear strip on motor

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my 2004 deville has a fuse box under the hood , near the front , on the passanger side . and a fuse box under the back seat on the drivers side . to get to that fuse box lift stright up on the back seat ( forcefully ) enough to disconect the seat from the car body ( two conections , one on each side of car ) then slide the seat forward and tilt the back of the seat up .

you can get new key a the dealer ship some cadillacs have a button on the shifter to unlock them.

On ABS light most common problem is ABS control module , they failing left and right.
As for the seat adjustment , sound like you need a new seat switch.

Try removing your seat bottom to access small motor that moves the seat,Tap on seat motors while holding seat switch in the forward position.

IT MEANS THAT A FAULT HAS OCCURED IN THE SYSTEM AND THE SYSTEM HAS BEEN DISABLED, TO FIND THE FAULT YOU MUST HAVE THE DEALER TEST IT FOR THE TROUBLE CODE THAT IS STORED WHEN THE LIGHT STAYS ON.

the electric motor for forward and back is bad salvage yard easy to change let me know hey vote for me ok

the seat wont move at all