Brakes pulsating while accelerating

toyota
tundra

#1

Okay so the brakes are not warped. As I drive down the highway at highway speeds what happens is the VSC seems to kick in and starts to break mildly at first and then aggressively harder until I stop. Once I stop the system resets and I’m able to drive normally. It doesn’t throw any codes and the dealership won’t do anything until I can replicate it. Seems to happen on long curves.


#2

How many times, and at what frequency, has this happened?

Model year of your Tundra?


#3

Usually happens after I rotate the tires so I am assuming it might be some lose wire and went away after one day or two. I just put new rotors on front so it happens daily now. I have a 2012 crewmax


#4

You know the same thing happened to my 2008 so I think the dealer may be screwing me. A good friend of mine had their brakes ruined by the same dealer


#5

The truck has an error in the vehicle stability control. The VSC thinks the truck is sliding or skidding when it’s not. A few questions; Does the truck have exactly the same tires on all four corners? With the correct air pressure? If not, it should.

Have the brakes been checked for dragging? If they are dragging that itself can confuse the VSC because if one brake is dragging the speed signal from that corner would be wrong. Its unlikely the ABS sensor has a loose wire as you suggest. If any issue with a loose wire occurs, the ABS and VSC will shut off.

There is also a possibility that the acceleration and yaw sensor - mounted inside the truck - has a problem. A scan of the ABS/VSC system while driving on a straight road should verify that.

You might want to try another dealer or a good independent shop if you don’t trust this one.


#6

Brake drag has nothing to do with it since the wheels still turn at the same rate, so the computer would not know the difference. Regardless the wheels are all the same size yes. No codes are thrown as mentioned previously. I just need to know recommendations on how to fix it


#7

No, that is wrong. Even slight brake drag will throw off the rotational rate. See the Wiki, Slip Ratio

But never mind me, I’m only an engineer that’s developed such systems for a major auto parts supplier.

I didn’t ask if the WHEELS were the same size, I asked if the TIRES were the same size.

As for CODES, I didn’t suggest you look for codes, I said scan the truck, in real time, so a trained technician can look at the accelerometer signal and the yaw signal to determine if they provide the correct readings on the road that causes your problems.

My recommendation on how to fix it is the last paragraph. Find out what is causing it to trigger the VSC by looking at data off the car.

If you are looking for some Magic Knob to twist or part to change, then go ahead and start throwing parts at it until it is fixed… Bring lots of money.


#8

My apologies. Please understand. I put the new rotors on and put the same wheels on the same hubs and then the problem started. I don’t want want to cause any problems on this site. If the VSC is so sensitive, it would have caused been a constant problem with my old tires, even after I put the spare tire on which was a different size. What company do you work for sir?


#9

No worries about causing problems… Most of the regulars stir things up from time to time. BTW, I worked for Delphi, a big parts and systems supplier.

The issue is not the wheels/hubs combo. It is variations in tire size. If you have the exact same tire SIZE but a different BRAND it can confuse the VSC as every brand tire is a bit different in width and diameter than another. Those variations are known to screw up Subaru’s AWD systems as well as stability control systems (VSC).

ABS/VSC controller reads the wheel speeds, an accelerometer, the yaw (turn) sensor and sometimes a steering sensor with inputs from the engine. From that it determines if you are turning and if you are turning too little or too much. By applying any one of the 4 brakes, the VSC can steer (drag) the truck in the correct direction and prevent it from spinning or pushing off the turn. You can imagine it doesn’t take much error in tire diameter to fool the VSC into thinking the truck is starting to spin when it isn’t. Since the VSC didn’t throw any codes it THINKS all is well. That means there are no errors in the sensors but that doesn’t mean the sensors are giving good information. That’s why a scanner that can read and plot the sensor inputs is essential to understanding what’s going on. A high resistance ground on a sensor may confuse the VSC into commanding a brake apply.

The fact that when it occurs, you can stop and reset the controls, hints that just maybe it is a software problem. The dealer may have flashed a software update assuming that fixes it when really it is sensor “drift”. But diagnosing that takes time that the dealership mechanic might get paid for so you can see the problem with getting them to spend any time on it.


#10

I fixed the VSC by turning it off


#11

Now that’s my kind of fix … lol … next time you visit a shop ask them to check the wheel speed sensors. If they’re properly geared up for Toyota repair, they’ll have the necessary equipment that will allow them to test if all 4 sensors are working correctly. What they do I think it put the vehicle on the lift then hand spin the wheels while they watch what the sensors are saying. Just one malfunctioning wheel speed sensor could cause this symptom, and it might malfunction in a way the diagnostic system couldn’t tell that the sensor had failed. This isn’t a rare problem here, you might search the CT forums on “wheel speed sensor” for other threads on this topic.