Abs booster goes off at low speed stops

They're right on top of the axle housing by where the axle goes in.

 

If it's the front wheels, look on the inside hub. You'll see a wire bundle going to the sensor which is fastened by one bolt.

Lastly, I still haven't had the issue return after I ensured sensor alignment in the bore. It's been over six months now

 

First off, thank you everyone for your replies. I have the truck in jackstands right now. Here is the drivers side sensor (I think…it’s the only other thing that doesn’t go to the calipers). It looks decent to me.

 

That's the wheel speed sensor. They are *probably* fine if you don't have the abs light on the instrument panel. When you reinstall them make SURE they stay straight in the bore. When you tighten the bolt it will tilt it towards the bolt due to it being offset. I would recommend you lightly sand the hub where the sensors attach to make the surface uniform. Rust builds up and may impact the way the sensors seat in the hub.

 

Bad WSS will sometimes do weird brake stuff, per other posts I've read here. You may want to check this thread: https://www.tundras.com/threads/slow-speed-abs-activation-fixed.131442/

 

I may have to take them off then. I just bolted them back in. I haven’t driven anywhere yet.

 

Good news is you can easily correct a tilted wheel speed sensor without lifting the vehicle. That's ultimately how I fixed it. Just slide under there and make sure the sensor is flush but not tilted. The fastener doesn't need to be cranked down, just enough to hold it flush.

If you still have issues I would get a scanner that can access live data and then drive and brake and watch the four graphs to see if a particular wheel speed sensor drops off line before the others do. I ended up buying a $20 wheel speed sensor from Amazon when I was troubleshooting. It did not fix it, but once I straightened the sensor out all my problems have gone away and I'm still using the $20 sensor today. I kept the OEM sensor and if the aftermarket one fails I will simply throw that one back on.

 

Truck is in the shop right now. I had an appointment to get it looked at again. We’ll see what happens.

 

This issue isn't very common on our trucks but out of the 6-7 people(myself included) that have had this issue on here, @jbryan76 and one other guy are the only ones that were able to fix it. I gave up and just pulled both ABS fuses. I tried 3 different wheel speed sensors, cleaned the tone ring, cleaned the sensor, readjusted the sensor. Nothing worked.

 

I would be very curious to see what the shop diagnoses. Please keep us informed.

You can also use a multimeter to check each sensor's resistance while spinning the wheel. Check the pins where the sensor harness plugs into the vehicle. The sensor will be disconnected for this test. The resistance should change with wheel speed. It may help identify a short or continuity issues.

You can then check the voltage to the sensor by using a flying lead or probe through the insulation directly. With the ignition to ON you can check steady state voltage with the wheel stationary as well as see the voltage change when the wheel is turned.

 

I will keep you guys posted!

 

Okay a little update- got the truck back from the shop yesterday. Right front wheel speed sensor was replaced. Abs pedal shaking under ten miles an hour has stopped. However the brake pedal is now spongey. It goes down and doesn’t really come back up. I have to put my foot under the pedal and lift it back up. They said they fixed that issues but they didn’t. Any ideas what is causing the mushy pedal?

 

Yup. Figured the WSS was either partly or wholly responsible. Telling you, weird shit happens when something ain't right with those ...

Pedal stuck down instantly makes me think excess vacuum, like diaphragm stuck, booster fail, or similar.

 

WSS?

 

wheel speed sensor

 

@bmf4069 it doesn't make logical sense how this could be the case but you were mentioning about how installing WSS perfectly in their hole is critical to things acting right. You don't think this weird pedal situation (see a couple posts up from today, not any day prior) could be related. do you?

 

Sometimes I really hate ABS…the whole master cylinder was replaced last year with an oem Toyota part. I’m not sure why the brake pedal sticks downwards. And it happened after the work was done at the shop. They did drive around and live scan and they really didn’t find anything that way with the scanner. According to them it was a difficult issue to fix. They said the exact same thing about the sensor needing to be dead center in the hole. It’s just frustrating as it’s been about 3.5 weeks since the truck was initially down.

 

Did you happen to go around and inspect all the hard lines just to make sure nothing is bent or kinked anywhere, both the lines along the framerails, in the engine bay area, and up to the back of the wheel? I'd expect a caliper to be sticking also if it were the case, and you'd really notice that.

Also curious, does it seem to be gone when the truck has been sitting for a while, and slowly ramp up to plateau while driving, as if heat is a factor?

 

I have not checked any lines but I will go do that right now. I don’t think a caliper is sticking and the brakes don’t pull to one side. I guess I don’t really know what you’re trying to say but I don’t think heat is a factor because it does it even when first starting to drive. It doesn’t do it, however, when I come to a full stop. If I brake and then coast the pedal sticks, but if I brake to a full stop it returns to normal pedal height when I take off again.

 

Based on your reply, I think you caught what I was saying.

Also based on your reply about the pedal, I doubt it's the lines now, and wonder if your booster shit the bed, is not adjust correctly, vacuum line is compromised or detached, or maybe diaphragm on MC is wonky. "Accelerate and the pedal raises back" is a pretty significant symptom which would point me towards booster/vacuum which is the first place I'd go. But someone else may know better.

 

Just to clarify the pedal doesn’t come back up because I hit the gas. It only comes up after coming to a full stop and then letting off the brakes. I don’t think it has anything to do with hitting the go pedal…I don’t think?

 

Brake lines look good also.

 

That is really bizzare that the brake pedal doesn't return. There is even a brake pedal return spring to assist in this. That means something is making it fight the spring.

 

This is why I was thinking there's a vacuum issue. I thought the pedal was spring loaded too, hopefully this isn't something stupid like the spring return detached

Sorry, I thought what I was reading was: You come to a stop, depressing the brake pedal. The brake pedal stays down. When you let your foot off, the brake pedal should come up immediately but it doesn't. Not sure how/why I interpreted things as you saying it returns when you start driving again.

 

All good! I just didn't want you to be thinking the wrong thing.

 

Do you guys know where I might look for a vacuum issue? Or maybe where could I check...

 

Do you have the fancy master cylinder or the brake booster master cylinder?

If you have the brake booster pictured below, you can pull the vacuum check valve (circled in red) from the booster and blow through it to see if it that's functioning properly.

 

Let me go look real quick!

 

Nothing...it's (the master cylinder) completely different that the picture you gave.

 

I'm in a pinch and can't find for the life of me the FSM page (or PHM's screenshot of it) that shows the process to test the brake booster for function. Anyone got that handy? I think it may help our brother here.