Is this a speed sensor problem?

[boomsticks]

I am having a intermittent speedo problem. the Speedo goes to zero or jumps for a sec. then the ABS light comes on and the then the Brake system light comes on and the DIC scrolls have brake system serviced. Also the truck doesnt shift past second gear.

It has happens a couple times in the past few days. Hot days. and after driving for a bit.

I took it my favorite mechanic, whos logic is always very good. But it wasnt konking out at the time(super frustrating). He seems to think it is the speedo konking out or maybe the speed sensor in the transaxle. since it doesnt store a CEL code and the speedo being out would cause the abs to go out and the trans wont shift out of second without a speed input... (i thought the computer takes the speed sensor data and feeds to speedometer. But idk)

My question is... does an AutoCal collect data in real time so I can drive and see what is happening in the system to cause the drivability problem? I would love to get a tune and hoping this would be my excuse to spring for it.

Feeling frustrated with my truck. looking for some help.

Anyone else have the same symptoms and find a solution?

Thanks

 

[swathdiver]

The Autocal collects data but I wonder if it is the data you need to solve your problem. A Tech2 can also do this. I have used both, what do you think we need to see? I'll see if my AutoCal recording has it. Being that we're two different generations may or may not make a difference.

 

[boomsticks]

Will it read save the data from the speed sensor on the transmission? So you can see it is that sensor? Or maybe it is my ecu messing up since it doesnt store any codes when ot happens.

 

[swathdiver]

Will it read save the data from the speed sensor on the transmission? So you can see it is that sensor? Or maybe it is my ecu messing up since it doesnt store any codes when ot happens.

I'm not sure that there is a speed sensor on the GMT900s. We have wheel sensors at all four corners. Let me pull up EFI Live.

Ok, It reads mph from the VSS (Vehicle Speed Sensor) which comes from the ECM, not the transmission, at least on my GMT900.

 

[Chubbs]

A good workshop manual will help walk you through something like this. Espc an online or electronic version which has loads more data than a paperback. I may try and look it up for you when I have time... It's just a LOT to sift through most of the time if you don't know exactly where to navigate. But it's there, no doubt.

 

[boomsticks]

I used my friends bluetooth obd reader the vehicle speed output drops to zero. Couldn't find any specific scans of the vss itself. Gonna take it to the mechanic tommorow and hopefully it will konk out and they can figure it out.

I got a speed sensor and swapped it into the two different spots on the transmission when the vehicle speed want being seen by the. Scanner and it still wasn't working. Maybe it is the wire from the pcm to the sensor?

 

[Rocket Man]

I used my friends bluetooth obd reader the vehicle speed output drops to zero. Couldn't find any specific scans of the vss itself. Gonna take it to the mechanic tommorow and hopefully it will konk out and they can figure it out.

I got a speed sensor and swapped it into the two different spots on the transmission when the vehicle speed want being seen by the. Scanner and it still wasn't working. Maybe it is the wire from the pcm to the sensor?

Are you saying there's 2 speed sensors in the transmissio? I'm confused.

 

[boomsticks]

Are you saying there's 2 speed sensors in the transmissio? I'm confused.

It sure looked like there are two there to me. I took them both out and they look identical. I took it into a shop this morning. It was konking out so hopefully the condition will still be there for them when they diagnose.

 

[swathdiver]

Are you saying there's 2 speed sensors in the transmissio? I'm confused.

The other is for propeller shaft speed (driveshaft speed).

 

[V30Crewcab]

if you have a 4l80 it has two speed sensors on the driver side. if its a 4l60 it just has the one in the tailshaft.