ABS Brake diagnosis help needed - 2005 LX470 with 112,000 miles

[dirtmerchant]

I've done a bunch of searching and reading but have not been able to find a similar situation as I've got going on, hope someone here can help.

This morning I had to slam on the brakes to avoid the soccer mom in the Escalate in front of me who panic braked for no apparent reason. Within a second of laying on the brakes I got a ABS feedback through the peddle and could hear the ABS activate; didn't hit the SM and all was good. That is, until I went to stop at the next traffic light. Now when I lightly press the brake peddle to slow down, I get pushback through the peddle as pressure builds in the system causing the SUV to slow more rapidly then it should given the amount of pressure that I am applying. As the pressure builds, it will instantaneously release and re-grab with a bit of a snap. The following lights are on intermittently ABS - VSC TRAC - VSC OFF

When at a complete stop with the motor running in drive. If I hold the brake with just enough pressure to keep the SUV from moving I get pushback of the peddle towards and I can feel pressure building, it will let the pressure off with a slight snap and my foot on the peddle will drop down about a half of an inch; agin, this is with light pressure, just what you would have sitting in traffic to keep from moving. The following lights are on intermittently ABS - VSC TRAC - VSC OFF

When turning the car on I hear the motor in the master cylinder run for about 30-second and shuts off, no strange noises and the fluid level is between low and max. The following lights WILL CLEAR upon shut down and start up ABS - VSC TRAC - VSC OFF but do come back in the above described scenarios.

So there you have it; any ideas????

 

[dirtmerchant]

Forgot to mention. I have owned this LX since new, it has been serviced by the books with complete brake flush by the dealer every 2-years on average with the last one at 90k and about 18-months ago.

 

[Scottb4857]

Maybe try "resetting" the system by depressurizing and then starting back up. Turn the truck off and pump the brake 40-50 times - this will depressurize. Then turn key back on - should take 30-50 seconds for booster pump to re-pressurize the system. Then pump the brakes 20 times. This should let everything normalize unless you have a bad valve or something.

Good luck!

 

[dirtmerchant]

Maybe try "resetting" the system by depressurizing and then starting back up. Turn the truck off and pump the brake 40-50 times - this will depressurize. Then turn key back on - should take 30-50 seconds for booster pump to re-pressurize the system. Then pump the brakes 20 times. This should let everything normalize unless you have a bad valve or something.

Good luck!

Scott,

Thanks for the suggestion. I went through the process x2. After I depressurized the system the fluid level went up to the MAX line, it took right at 30-seconds to re-pressurize and fluid went back to the halfway point between Max and Min. All lights have been extinguished but I am still getting the pushback and I am coming to a stop from a slow roll I can hear a high pitched squeak like fluid through a valve; didn't notice this before but it may have been there as it is acting the same...

Any suggestions as what to try next or what is wrong that needs replaced?

 

[Scottb4857]

I would say at this point it will need to be hooked to a tester and run through the diagnostics. If the dealer finds anything wrong most likely they will immediately suggest their standard fix which is replace the entire master cylinder assembly. Depending on the dealer that will run anywhere from $2500 - $3500. Hopefully someone else on the board reads this thread and has some suggestion I'm not thinking of that is better than this.

 

[dirtmerchant]

Thanks Scott,

I've got an appointment to take it by local Lexus Independent shop for diagnosis and estimate, I'll report back...

 

[dirtmerchant]

Following up to close my portion of this thread.

I took my LX470 into a local Lexus/Toyota Independent mechanic. He drove vehicle and read the codes with laptop attached while driving. Said only code was for high pressure, thought it may be malfunctioning pressure sensor. Advised to bring it back when I had time for hime to test out with another sensor that was known to be good before rebuilding or replacing anything.

Since the problem occurred immediately after activating the ABS in traffic, I decided to once again active the ABS to see if I had a stuck valve or whatshacallit... Low and behold, after activating the ABS on gravel road it is working as designed. I will update this thread if the problem reoccurs and subsequent fix.