what does it mean when your speedometer dances and your engine High revs like it's trying to go into neutral at highway speed? speed sensors? are these the same ones that trip the ABS light?
99 bravada 4.3 awd (two-month-old tccm) on wet salted Highway @ 23deg.F

 

sounds like Tcase might be on its way out, are you sure its an AWD as i dont think GM made any AWD Blazer or S10 based vehicles.

 

TCase sounds threatening and promising at the same time lol. the all-wheel-drive was given to the bravadas and shared with probably the Astros and maybe the early vues / equinoxes. it's a full-time spin, zero-button, LOL.

 

Mine did it. It's the sensor on the rear end housing. Pretty sure it's an ABS sensor. Maybe it's the speed sensor. I can't remember, either way the computer doesn't know the wheel speed so it whacks everything out. Cheap fix. I had my mechanic tackle it due to lack of free time and I needed it back it a couple days. Think I had $150 in it?

 

awesome info, I'm so glad I'm not the only one! the only thing I hate is getting ghost symptoms that nobody else experiences. thanks a ton and that explains a lot of other things as well lol, like my overhead computer console telling me my average speed is 18 miles an hour when I am on and off the freeway daily. even just to Crosstown LOL.

 

I had it briefly do it once or twice prior to it totally taking a crap but it was always at low speed locally. Worried me, but it was so brief it had me thinking the trans was acting up. Never got to see the speedometer jump around because of the low speed. Was traveling at highway speed when it finally didn't want to work anymore, noticed the speedometer jumping all around and the trans going to neutral(I'm assuming it's a safety feature since the ECM/TCM, whatever is reading wheel speed, doesn't know what's going on) as well as the ABS light on and the Brake light. Luckily I wasn't far from home so I limped it to the shop. Glad I could shine some light on your issue.

 

Just looked at my invoice from when I had it fixed. Wheel speed sensor. Part was $54, had $170 in it between the part, diagnostics, and labor.

 

okay so I'm horrible at posting resolution quips, but this one apparently didn't last very long. so a local shop determined right front hub speed sensor was bad / no signal. they claimed that nobody changes speed sensor is on Old hubs anymore so they would only replace the entire hub. I asked if the wheel bearings were bad in that and they said they were starting to go. Go figure. I am an essential worker so throughout covid-19 last posting in March until now I have been daily driving about 20 miles. when I got the truck back the ABS behaved and this cruise control worked and the high revving was gone. so now it is back and worse. speed sensor is tripping out speedometer and making tranny act like no second. also canceling cruise control randomly on Highway. again with other posters that mentioned to me in March about low speed, my low speed ABS started activating again and the transmission like symptoms only happen if I try to stay between 25 and 35 miles per hour. if I intentionally and aggressively stand on a stop to 45 mph the tranny will not do it at all. this is the same shop that also charged me a hundred and forty-five bucks to essentially tell me I ran out of gas, when I panicked into worrying about the previous owners installed fuel pump. Their diagnostic fee is upfront and 1st, and not folded into subsequent repairs. I really really hate the idea of taking it into them and paying them to tell me it's not their speed sensor because I know that they will.

 

It sounds like you have two problems; a VSS issue affecting the trans & speedo and a WSS affecting the ABS with low speed activation.

As far as not replacing a speed sensor in a hub, that sounds like the easy way out. While more often than not, the hub can be the source of the problem replacement should not be the first step in diagnosis. There have been A LOT of cases through the years where rust buildup under the wheel speed sensor mounting tab has caused it to lift, opening the air gap beyond spec causing low output resulting in low speed ABS activation. There is a TSB from GM on this very thing. If the WSS comes out without breaking, a quick clean up and reinstall followed by verifying in spec mV-AC output of the sensor. In fact, that is the first step in a proper low speed activation diagnosis, verifying the mv-AC output of both front WSS. The details are in the Brakes - Low Speed (below 5 MPH) ABS Activation [SPEED SENSOR TESTING & ADJUSTMENT] tech article.

I have had brand new hubs fail in the first few hundred miles. It sucks, but happens even with high quality hubs and even more so with lower quality ones.

As far as the VSS goes, It can be tested similarly to the WSS, but I could not find the specs as to its output. You could start by removing it and inspecting the end of the sensor for debris. Metal debris on the end of an inductive sensor will cause erratic readings.

 

It was actually all from the VSS on the t-case. the weather sleeve on the connector itself was completely missing, the sensor and the connector were both completely corroded. Apparently they are now dealer only parts for a 99, but they were not bad at all other than 120 total. I found a new shop with a mechanic who loves integrity and building customer respect... weird. 234 out the door. Bravo's got a new family doctor. he even suggested a double bypass surgery if the harness wires still provided too much resistance but he said for now they are fine. he was literally going to rewire the ABS outside the main harness from the VSS to the vcm. he said that can still be done later if it becomes an issue.