I posted about this a while ago but have come upon some new information that I thought was interesting. My h2’s brake system is in perfect condition. There are no leaks or seeps anywhere, all the brake lines have been replaced with stainless, and a year ago replaced the whole master cylinder/abs/booster unit. And have experienced the same odd behavior throughout my entire ownership, and my parents who owned a different 08 when it was brand new, said it was the same way.

That is the spongy pedal. After a fresh bleed and abs bleed, the pedal is great. Most confidence inspiring brakes I’ve ever felt on any vehicle. It’ll lock up all 4 wheels at 70 before abs kicks in.

However, the pedal becomes spongy over the course of a month. Now it will never get so bad I can’t stop the vehicle, but it gets to the point where you have to press the pedal about half way down before you get much stopping power. And the pedal feel diminishes even faster after towing something heavy or off-roading and using the brakes hard. A day of off-roading in the mud sometimes equates to a month of normal driving if that makes sense. The pedal will be pretty dang soft.

Now the temporary cure is to just do a single abs auto bleed with a tech ii. Takes all but 5 minutes. And it has to be a tech ii. After market scan tools activate the solenoids too fast and don’t let the accumulator rebuild enough pressure to push the air out. After this, pedal is back to perfect.

Now take a look at these two pictures before and after the abs bleed. Pay attention to “brake pressure sensor 1.” Both readings are with the pedal pushed to the floor before and after an abs bleed.




There is almost half a volt of difference! While that might not seem like much, half a volt from a brake pressure sensor is a big difference in pressure. Especially since voltage is not linear to the actual pressure reading. And you can definitely feel the difference in the pedal.

This, while inconvenient, can very well make the difference between crashing and not crashing!

For a little more context I spoke with a guy I work with who was a Toyota tech for many years. This same or similar unit is used in the trd pro Toyotas with a-trac and the Prius of all vehicles😂 He said they all kind of had weird braking behavior. I’ve also seen a few Toyota forum posts about this same thing. No one has an answer. It’s just “how it is.”

That’s really concerning to me. How is air getting into the pedal cylinder in just a month “normal”??

And it’s not like it’s any other component causing this since it’s all brake by wire. The calipers aren’t physically connected to the master. The master’s only job is to create pressure for a sensor to read. Or take over in the event the system fails.

Im genuinely surprised there is not a lawsuit over this or a recall. Its dangerous if you ask me.

Has anyone experienced this with their 08/09 or h3 with the same unit. Hell even with a Toyota?

 

How old are the calipers?(worn caliper seals can suck air without leaking)
What's the DOT rating brake fluid are you using?(overheating the brake fluid causes air bubbles)
Did you test the

Brake Fluid

Brake Fluid

?

 

Brake fluid is new dot 4. Calipers are oem. The master cylinder is not hydraulically connected to the calipers anyway, so in theory air can’t travel back up into it. Also if the calipers were letting air in, an abs bleed wouldn’t fix it.