[RADman2000]

Try replacing the K134 Multifunction Relay Module (part number 90 494 163). Location is mentioned elsewhere in this forum. It's about $53 from gmpartsdirect.com, and it's a 10-minute job to replace, once you find it.

OK, here's how to get to it (mine's a 2000 Catera--I assume it's the same for your '99, but not sure):
1) Remove sound-deadening panel that sits directly above the pedals. Also removing the knee bolster (panel covering fuses) might give you a little more room.
2) Get on your back, feet out the driver's door, and slide in so your head is next to the accelerator pedal. Now look toward the fender for a gray box (K134 module), about the size of a thick pack of cigarettes.
3) Note the orientation of the module, then push directly up on the module to remove it from its bracket.
4) Push clip on plug and pull plug out of the module.
5) Plug in new module
6) Orient the module as it was when removed, then position it above the bracket and slide directly down until it seats.
7) Replace sound-deadening panel.