2017 Toyota RAV4 111,200 km
After an emergency braking to avoid an accident, my brake pedal will slowly go to the floor when stationary and the engine is running. During the initial investigation, we found that the brake fluid had deteriorated and was almost sludge-like brown (the fluid was replaced 1 year ago @ 104365km). After replacing the cylinder with a used one. It operates normally when driving at normal speed but still loses hardness when the vehicle comes to a stop or in traffic and the vehicle will begin to creep. There are no trouble codes for the ABS shown, I’ve replaced the master cylinder again with a new genuine Toyota brake master cylinder, bled the brake using manual steps and used the bleeding procedure using a scan tool (ABS, TCS) and the issue persists. Please help as this renders the vehicle unfit for driving
Sometimes it's very hard to get the air out of the system, but if you have I would assume that the brake booster has been damaged from the emergency stop. But you did say there was a lot of sludge in the system and that can clog up all kinds of things in the ABS system. That would be virtually impossible to get out without just replacing the ABS module. If it's sludged up, it often won't work right but it won't trip and he codes cuz the general. I only trips colds when there's electric problems with solenoids
@scottykilmer Hey Scotty. I am leaning more toward the ABS but if the brake booster was =damaged wouldn't the pedal be harder to press? THe effort is the same it's just that it doesn't stop until it reaches the floor
@scottykilmer The Issue was narrowed down to a faulty ABS Modulr actuator.
Hey Scotty. I am leaning more toward the ABS but if the brake booster was =damaged wouldn't the pedal be harder to press? THe effort is the same it's just that it doesn't stop until it reaches the floor
Scotty typically answers questions once and doesn't revisit them.
You would be correct in thinking a defective brake booster usually causes a firm or hard pedal. Soft and sinking pedals are usually caused by such things as a leaks, air in the lines, defective ABS module. When you're dealing with a brake system that's had "sludge-like brown" brake fluid in it, you very well might have to replace multiple components.
@hixster THe issue ended up being a faulty ABS actuator module> I got a used one from a totalled car and one on the brakes returned to normal. Many thanks guys.
@jaysmall Glad you're back on the road, thanks for the update.
Try removing the ABS fuse. It's worth a try.
@oskool How would this work exactly?
@jaysmall Removing the ABS fuse will cut power to the ABS unit. This will stop the solenoids in the ABS unit from manipulating the brake line pressure. Although it might not work because the valves inside the ABS unit might be gunked up and stuck due to dirty brake fluid. https://youtu.be/-IUZWwMm7nY
Now that I understand better how ABS units work, I'm going to start opening the bleeder screw during brake jobs to prevent pushing contaminations into the ABS unit.
A great video showing the teardown of an ABS unit. I had no idea how many valves are inside. The video shows a hydraulic circuit diagram of an ABS unit. I count 24 valves in the hydraulic circuit diagram. https://youtu.be/qHf1qo31-aw?t=531