Hey everyone i have a 99 bravada and it wont shift out of first gear and the speedometer quit working. I have already changed the vss and the ignition switch. Still no shift or speedometer so im trying to figure out what to do next. I had it put on a diagnostic scanner and it said that the vss was not present. Maybe the harness to the transfer case with the vss wires in it? Have any of you guys had this experience? Any help would be greatly appreciated!

 

The VSS is connected to the VCM on your passenger fender behind the overflow bucket. But the transmission should be able to shift without input from it (VSS that is)...... In the underhood fuseblock check fuses ECM 1 and ECM B, in the IP fuseblock check the GAUGES fuse and the CLSTR fuse. What was the specific code? PO500? Was that the only one? A transmission specialized scanner would have 503, 504, etc.

 

the code the first time i checked them with my scanner was a p0502, i then changed the speed sensor and that did not fix the problem. i checked all of the fuses(inside and under the hood) the atc fuse was blown. i replaced it and it blew as soon as i turned the key on. when my friend checked it with his scanner it didn't bring up any codes at all, but that was probably from when i changed the ignition switch. he tested all of the circuits and all of the sensor on the whole truck and it just said that the vss wasn't present or something to that effect, and he said it also needed a front wheel speed sensor(it was making the abs light come on). i thought that if the vss quit working then it wont shift because its all electronic(without the speedo it doesnt think its moving)? man this thing is kickin my butt. thanks for the reply and any help you can give will be really appreciated.

 

The CLSTR fuse powers the valve bodies in the tranny (computer controls grounds). I mention that because I know if that fuse blows and the valves lacks power it defaults to 1, 3, Reverse. That's what struck me as odd, even if the VCM can't control it the tranny has a "drivable default" mode. As for not seeing the VSS.... Running over the top of your transfer case is a small harness with a 2 pin connector above the case - PPL/WHT and LT GRN/BLK wires. That connector is the two wires between the VSS and VCM. You might have the problem there.

 

thanks ill check it out some more. the wires for the vss go directly from the vss to the vcm? i can manually shift from first to second and it has reverse. i'll keep ya posted on what i figure out. thanks again.

dustin

 

If you had 2WD it is direct but the 4WD has that additional connector in between.

 

yea its AWD it has smart trac

 

well i checked the voltage going to the speed sensor and there was no voltage. so im not sure what to do next. sounds like changing the harness is gonna be a pain.

 

I'm too lazy to type in the entire diagnostic flowchart <G> but here's a synopsis of things to look for: The blue connector to your VCM, remove it and looking at it with the clip down, top row, pins 3rd & 4th from the right go to your VSS. It should measure a resistance of 976-2354 ohms. If you put the tranny in neutral, have someone hold one wheel & turn the other. VSS should generate .5V AC. If you measure (at the VCM connector) between the pin 3rd from the right to ground it should be greater than 50,000 ohms. If you pull the connector off the VSS and turn the key on (don't start) and measure across the harness connectors it should be between 4-5.1V DC. BTW the connector I mentioned before is above the tranny a few inches in front of where the transfer case bolts on.

 

ok, i'll check it out some more. i checked the voltage once today but now i can't remember if i did ac or dc. i'll check the resistance at the connector at the vcm. i was looking at the wiring under the truck and it looked like it was gonna be a pain. thanks for the help. i'll do the stuff you said and let ya know how it works. thanks i appreciate the help.