Flagolfer

Hello fellow GX drivers,

I want to share an experience that is still a mystery to me with my 03' GX470 with 144k miles.

A couple of weeks ago while out of town waiting in the drive-thru of a restaurant, all of sudden my ABS, Brake, VSC, etc light comes on and the brake paddle becomes hard as pushing a 2x4 where brake becomes disabled and doesn't work. So by using the emergency hand brake to get through the line, and meanwhile, the brake goes from hard as a board to soften state like a regular brake which grips. This process continues intermittently. I took some risks to drive a couple of miles to a large parking lot of a school where I called Uber to get home. I had brake fluid leaks, master cylinder failure, and a few brake problems over the year of different vehicles, but never like the situation I described above.

Here is the mystery: The following Monday, I had GX470 towed to my tire/mechanic shop I've been going since 1995. The head mechanic calls me and recommends to take it to the Lexus dealer. He said it seems like a brake hydraulic related issue and didn't want to mess with it. I had it towed to a different mechanic who fixed my 07 GX450h's ABS brake assembly last year. He calls and recommends taking it to the dealership, stating he had tried to a similar issue in the past but without a success. And since the Toyota dealership was much closer, I had it towed to the dealership. The next day the serviceman calls and tells me that the GX needed to replace the complete brake assembly including the master cylinder and cost OTD is $4100. Weighing risk/benefit analysis and a bit of desperation, I take it to a different mechanic my sister had used. (The mechanic from her neighborhood who used his home garage to start building his business and hungry to grow and now has a bigger shop). He calls me the next day. The GX wouldn't start so he replaced the battery and since then he put 5-mile driving without any brake problems. I asked him to drive more miles and told him to be careful. After his shop mechanics driving it over five more days and an additional 25 miles without any brake issues, the mechanic thinks it was a voltage issue, although he wasn't completely certain. He said he has seen a low voltage cause all kinds of weird mechanical issues.

So, I am happy to be driving my GX and paid less than 10% of what the Toyota dealership quoted. I have now given a nicknamed my GX: Butter (since it's so smooth).

Has anyone had a similar breakdown due to the brake issue I described? If so, what was the solution for you?

Thank you in advance and I hope by sharing my experience, it can help someone else.

chiph9

It was possible it was low voltage.

The GX doesn't use the typical vacuum assist brake system, it uses an electric-motor driven brake assist system (brake booster). And they have been known to fail once they get old. Parts cost is about $3300, so $4100 with labor is high, but not crazy high.

https://www.mylparts.com/oem-parts/l...QtN2wtdjgtZ2Fz

I would keep a careful eye on it, and at the first hint of a problem (I like being able to stop...) I would get it towed to the mechanic and either put a new master cylinder in, or scrap the vehicle, depending on the economics and your desire to keep it.

Chip H.

Flagolfer

Hi Chip, thanks for sharing your insight. We bought it new in late 2002 and have been in our family, Father-in-law to us. He has RX now but can't drive due to his condition, sadly. I am really hoping to ride this out 1/4 million miles or so. But will have to see.
Any suggestion to look for things to prevent? I have been reading GX forum a bit but since I am not DIY, I am concerned.

Thanks again.

Toys4RJill

Could be pending alternator as well. I have 4Runner, same chassis system and parts as your GX, when the alternator was about to go, the brake lights all lit up

Flagolfer

Ha, thanks for the heads up. I just texted my mechanic "what if" since there is a slow churning noise (sounds like the electrical motor in directly front of the driver seat, and a whiny noise at the start of the morning till warms up). Plus, I added your comment "could be pending alternator." I'll know in a few days and if anything new, I will report.

Flagolfer

I was at the mechanic shop picking up my daughter's Civic. I asked him about him checking the alternator of the GX, and he said it was good. So... the mystery is still there while I drive my Butter.

childerj

I just had this happen yesterday. The sporadic whining sound right in front of the driver's seat followed by the brake alarm and dash brake lights about 3 miles later. I didn't lose brake assist but did immediately take it to my garage. Half way to the garage all of the lights went off but I went ahead and took it anyway. They diagnosed it as an internal leak in the Master ABS motor system which causes it to overheat. They explained what was said above about the GX having a motor assisted braking system which is dangerous if it stops working.

They are getting the entire Master Cylinder/ABS assembly from Lexus for $1879 and $400 for the install so not as bad as what you experienced.

SilvrGX470

The noise you describe in a previous post is the small electric motor that drives the pump to charge up the nitrogen charged accumulator on the brake master cylinder. As your vehicle ages, this motor will wear out and get louder. Plus the accumulator will gradually lose its nitrogen charge, which causes the electric motor to run more often, and thus accelerating the wear on the motor. Toyota/Lexus will suggest to replace the entire master cylinder assembly because that's how they sell it. But, you can replace the motor and the accumulator individually for less than $1000. For reference, the electric motor should be practically silent and should only run occasionally.