Speedometer dies and Trany slips (at same time)

[vljenewein]

A few days ago I noticed that my speedometer went to zero when I was driving and stayed there.. then misteriously started working again next time I drove the car. Did it a few more times as well. I'm thinking, the gear must be getting worn. I now believe there is no gear and it's electonically controlled.

However, tonight I'm up in Holland, MI (north about 20 miles) and heading home and the motor revvs up, transmission is slipping and the speedometer is down on zero again. Pull over. Turn off engine. Restart car and now the transmission works, but it acts like its sliping quite a bit. I ease up the streets a bit to a parking lot with some lights, Check out the fluids, etc and all ok. When I start it up the speedometer works, transmission works and I head on down the interstate toward home. Stopped about 4 miles from home for gas. Now, when I leave the station, I give it some gas like I usually do and the speedometer drops to zero and transmission slips again. Pull over and stop engine. Restrat and drive home, but speedometer is still at Zero, and things seem a little "not right" "Service Engine Soon" light comes on and stays on. Is it a modulator, relay, or some other malfunction? Seems the transmission and speedometer are closely related in this problem. AND it appears to be mechanical/Electrical and not from low or our fluids.

Any guesses or have heard of similar problems?

[parkavenuechrome]

your correct, the transmission is computer controled and so is the speedometer. If your speedo drops to zero and the trany slips, then there is an issue with the ECM or wiring to it. More than likely the ECM is faulty ( computer ). If the trans was slippin and the speedo was ok then i would suspect a trans issue, but its more than obvious that it is electrical.

[vljenewein]

Thanks for the reply back! I did some digging around late last night and without hooking it to a computer, I suspected a faulty VSS (Vehicle Speed Sensor). Bought one from Autozone at lunch time, and put it in after I got home. Would have been nice if not raining!! LOL The VSS was over on the passenger side and has 2 wires that go to it and is held in place with a tab with a hole in it, and attaches with 1 10mm bolt. There was some metal "fuzz" on the old unit I pulled out. Plugged it back in and tried it. No go. DARN!! Speedometer still reads as ZERO and stays in 1st gear and then "Check Engine Soon" light comes on if I try to accelerate. Probably 'thinks' it's sitting still, or barely moving, and since there's no forward movement the tranny belives i'm barely moving.. no need to shift into another gear, right??

Any way to test out the ECM? Could there be a bad connection up inside the car where the VSS connect to finally? I do believe it's something electrical, as I was saying, in Holland, I got it started and put in gear and the speedometer was reading. Drove 20 some miles down interstate around 70-75, shift normal, no issues. Got gas started out normal from the station and speedometer worked, but then....died. So did the ability to shift. As long as the speedometer worked the rest of the transmission seemed to work as normal.

I bought the car about a year ago and it had 89,000 miles on it. Took it in for servicing at the Buick dealer around that time as well. But when it rolled over the 100,000 mark, it did NOT roll over to the 1 position, but stayed "000000.0" When I first got it tires were worn out, all shocks were needing replaced, shortly afterward I replaced the right wheel bearing. just wondering if it had 189,000.0 on it from the beginning and actually rolled over the 200,000 mile mark.. Shesh!

[Jed Rule]

The PCM uses the VSS signal to control the transmission shift points . The sensor must be fully seated in the case to magnetically read the speed of the teeth turning on the output shaft in the trans just under the hole for the sensor. Was the other sensor end damaged when you took it out? Try removing the sensor and examining the teeth through the hole while you rotate the L/f tire. The fact that it got worse with the new sensor leads me to suspect a problem there.
If that looks good, you are going to need someone with a scanner to see if the PCM is reading the VSS. There could be a problem in the wiring between the two, or at the connectors . Did you clean the fuzz off the VSS connector terminals when your replaced it? If you have a digital voltmeter, test for .5 volt at PCM terminal RB3 (yellow wire) with the engine running and the front wheels turning at low speed. Be sure to support the front end at normal height to avoid stressing the axle boots. If there is no voltage, there is a problem in the wires or the VSS. If there is .5v there you could have a bad PCM.

[vljenewein]

"The PCM uses the VSS signal to control the transmission shift points"
Ok.. what is a PCM? That one has me stumped.

"Did you clean the fuzz off the VSS connector terminals " The "fuzz" was on the internal round piece of the FSS.. that which fits insdie the transmission. The gray fuzz is probably metal picked up on the VSS. I might try checking out the wires where they plug into the Vehicle Speed Sensor. They looked like they had seen better days. If I put a ohm meter on the wires and to the body that should tell me if there is a ground on one of them. Of course one of them MAY be a ground anyways.

Got codes 12 (normal 3 series flashes), then code 24 and then finally code 66. My A/C has been getting worse and worse on me and I suspect that I need to get a recharge. I think this code 66 is picking up on that. I used to be able to put on the A/C and get kind of cold air, but it would kick off into the "economy" button pretty quick. Now the "automatic" button won't click on for A/C.

Perhaps the new sensor is faulty. That has happened. Not very likely, but possible. If the tire spins and I put a volt meter on the one prong on the VSS, would I get some sort of voltage from it? Any way to check the unit out before returning it to Autozone?

[Flatrater]

Look at the wires on the VSS real close. Tug the wires one at a time I would bet one wire is broken inside the insulation. When you tug on the wires if the wires turns colors then you have a broken wire inside.

[vljenewein]

Went up to Holland at "U-Wrench-It" today and got a plug connector off a GM that has the same kind of module. I have about 6" of wire and have those red 'butt' end connector to attach to those yellow / purple wires and the one on my Buick. By chance if there is a difference in color schemes on my Buick, stick with yellow to yellow?

[Jed Rule]

The PCM is the Power Control Module (also known as the COMPUTER). My 95 service manual shows a yellow and a purple wire to the sensor. They come directly from the PCM. Yellow goes to terminal RB3. Purple to RB2. Check the connector carefully as Tman says.

[vljenewein]

Thanks Jed! I replaced the connector that goes to the VSS from one I got in Holland. I checked it with an ohm metere and checked out alright..good contact on each of the 2 connectors, Yellow and Purple. I drove it again and no speedometer yet. And, of course still shifts 1st to 2nd oddly. I retested with the code scanner and got codes 12, 17, 24, 56 . Is that RB3 and RB2 under the hood or inside of the car where you referr I check?

[vljenewein]

Well it's fixed! I was looking under the dash on the passenger side for the yellow and purple wires, moving some wires around when all of a sudden a big mass of wires just comes unplugged. There must have been 25 or so wires going into that plug-end that plugged into a silver box. It had a Blue connector on it. I pushed it in untill I felt it "click" in place and lock. Then I drove the car. Speedometer worked, and so did the transmission shifting. I cleared the ECM memory, and re-drove the car. Performance was crappy but it will "learn" and become a bit better. I checked the diagnostic code scanner and the only codes I get now are 12, nothing more.

So, I spent $47.00 for a new VSS to replace a VSS that probably worked alright. Another 3.00 at a wrecking yard for wire piece. $39.99 for a code scanner (I can keep it and reuse it though). All for a main connector that probably wasn't fully seated. Do I get the DumbSH*t award for this?? LOL

Anyway I just wanted to report back on the progress and what it took to correct the problem. Could be someone else out there with similar problems and they can read the prior posts and also get pointers and tips from them as well.

[parkavenuechrome]

So the Computer ( ECM , PCM ) was coming unplugged... That will do it in a heart beat.. glad you all set!