Speed sensor?

[Suburban_Tyler]

I noticed a couple days ago on my 90 R1500 that when I came to a stop that my brake pedal would pulse something like once a second like the abs was kicking in but being really slow or a caliper was sticking on the slides or a piston was bound up. Pedal doesn't seem to go down further with the pulsing settling, feeling. It didn't do it every time I stopped. Just sometimes. The suburban didn't really pull one direction or the other when i applied the brakes. It did seem to take slightly more pressure to stop. I'm a very casual driver. I jumped in the suburban last night and noticed the brake light on the dash being on. I set the parking brake and it lit up a little brighter so I know it wasn't that. I unplugged one of the plugs on the abs controller and plugged it back in. It sounded like something rest inside of it. The brake light also went off. I drove around town a little while (30-35mph) and noticed the converter locking up for a second and then unlocking again. It did this a few times before I hit a hill and it stayed unlocked. That's when I noticed the speedometer going up and down 3 to 5 mph. I got up on the highway, the converter locked as it should have. The speedometer started going up and down 20mph. The brake light came back on. I unplugged it and replugged it again and the light went off. I drove it again and recorded an almost 9 minute video I will hopefully share on here. The bouncing of the needle came and went but right at the end is when it started going crazy and the brake light came back on again. I unplugged the abs controller and left it unplugged. The light went off and stayed off. Speedometer still bounced. I don't know if I have multiple issues or if they're related. I do have the electronic sensor in the transmission for the speedometer. I know or at least i think I know that the abs probably reads off the same sensor. What I am unsure of when the pedal feels like its pulsing. Is it the abs actually activating or is something not moving smoothly all the time and I am feeling it moving in a motion that makes it feel like its settling in a jerking bound up motion. Hard to explain that one.

Here's the video. Don't pay attention to the squeak of the center console lid or the toolbox in the back with the rattling tools. I've got a tire that nobody can seem to balance.

Speed sensor - YouTube

[Ski-me]

I can't see the video at work (blocked), but it sounds like it's your speed sensor. It's a 2WD truck right?? So I'm guessing the pickup is on the tailshaft of the tranny. There should be a two wire connector that plugs into the sensor (purple and green, I believe) and continuously twisted. This is where I would start.

Trace that twisted pair from the sensor all the way up to the truck DRAC box (on passenger side behind glove box I think). Make sure the wire is not damaged or grounding out somewhere on the frame. It goes to your DRAC box and then the truck computer. The DRAC converts everything and then sends signals to speedo, cruise, abs and computer.

The solid brake light indicates problems with your ABS (rear only I believe). If it's not getting a correct or a fluctuating speed signal, this may be why it's tripping. Because your speedo is also moving around, leads me to believe it's either the twisted wire or the pickup sensor on the tranny. If the wire is good, you might try replacing that sensor (can't be too expensive).

You can somehow get the abs codes too, just don't recall how you do it.

[Suburban_Tyler]

Originally Posted by Ski-me

I can't see the video at work (blocked), but it sounds like it's your speed sensor. It's a 2WD truck right?? So I'm guessing the pickup is on the tailshaft of the tranny. There should be a two wire connector that plugs into the sensor (purple and green, I believe) and continuously twisted. This is where I would start.

Trace that twisted pair from the sensor all the way up to the truck DRAC box (on passenger side behind glove box I think). Make sure the wire is not damaged or grounding out somewhere on the frame. It goes to your DRAC box and then the truck computer. The DRAC converts everything and then sends signals to speedo, cruise, abs and computer.

The solid brake light indicates problems with your ABS (rear only I believe). If it's not getting a correct or a fluctuating speed signal, this may be why it's tripping. Because your speedo is also moving around, leads me to believe it's either the twisted wire or the pickup sensor on the tranny. If the wire is good, you might try replacing that sensor (can't be too expensive).

You can somehow get the abs codes too, just don't recall how you do it.

It is a 2wd. I ended up replacing the speed sensor on the back of the transmission and the speedometer started working correctly. The brake light has stayed off since then.

[Ski-me]

Originally Posted by Suburban_Tyler

It is a 2wd. I ended up replacing the speed sensor on the back of the transmission and the speedometer started working correctly. The brake light has stayed off since then.

Awesome! Glad you got it working again......

[Suburban_Tyler]

My dadgum speed sensor is acting up again. I kinda thought something was up when the brakes started acting funny again. Sure enough on my way home this morning from work I saw the speedometer needle bounce around once. On my way back to work this evening it did it again. I guess the Duralast part was in fact NOT built to last. I'll blame this one on faulty part this time. I will try a different brand and try again.

[Suburban_Tyler]

Once again I got the speedometer calmed down and the brakes aren't acting up. I put another sensor of a different brand in(Master pro) I wanted. It acted worse than the Duralast I took out. So I took another look thinking I didn't have a good connection. I pushed in on the wires to make sure they was seating into the plug fully and one wire folded like it had a soft spot. Sure enough there was a broken wire inside the insulation. I could push in on it and everything worked good. I bought a pigtail for it and put it on. So far everything is working good.