Another ABS/VSC Brake Question

[tesq]

For background, since I became the new owner of my 2007 LX470, I've noticed the master cylinder accumulator pump running really often. Like, after just one application of brakes, the pump would kick back on. A few weeks ago, I got in to start my car and the pedal went to the floor. It also felt like the pedal shifted to the side slightly, like it had misgrooved. Upon starting up the car, I was greeted by the christmas tree of ABS VSC TRAC and Brake. It also sounded like the Brake MC accumulator motor didn't make its usual hum. Releasing the brake pedal seemed to solve everything and the lights turned off and the car went back to normal. I checked the codes, cleared the main ecu codes*, and didn't notice anything else for a while.

A week or so later, I was driving down a short hill when I again had the ABS VSC and TRAC lights illuminated. No buzzer. They went away very quickly, basically after I finished braking at the bottom of the hill . I pulled over and used an OBDII reader to pull the following active and historical codes:
P0504 (Brake Switch A/B Correlation)
C0278 (Open/Short in ABS Solenoid Relay Circuit)
C1223 (General ABS Malfunction)
C1246 (Master Cyl. Pressure Sensor)
C1253 (Hydro-Booster Pump Motor Relay)

Of note, I was able to communicate with the ABS/VSC computer without any issue.

Now, I'm somewhat afraid to drive the LX470. Interestingly, I don't have any multifunction indicator lights on the dash: just the P0504 code in the main OBD network and the others in the ABS/VSC network. If I reset the codes, everything operates normally for a while until during or right after a "hard" braking condition, where the lights pop up then disappear but the codes remain.

For the p0504, I'm thinking that my extra-hard pedal push that one morning might have damaged the brake switch or the little plastic interface piece. For everything else, these feel like an ongoing brake master cylinder assembly failure. Maybe the p0504 is related to that as well. Does anyone have any insight into what the issue might be? Or troubleshooting steps? I plan on having the car taken in to a Lexus dealer for diag to be on the safe side.

 

[TequilaMechanic]

Hey I had similar reservations and issues and am replacing my whole brake booster assembly. Since it’s $1300 just for the part you probably should troubleshoot further, If you want to troubleshoot more, download the FSM and search those codes in the diagnostics document. Some exerts below for ya.

Having the system turn on the pump/motor after one use tells us that either you have low fluid, a controls issue, or low pressure in accumulator. How’s your fluid level? With car off, on level ground, pump brakes 40 times and then check. Are you leaking fluid? Has fluid been overfilled ever?
Honestly not sure if the car is safe to drive.


I had the following issues:
4 warning lights and audible alarm. Hooked up a code reader and gave me codes
C0278 - Open or Shut Circuit in ABS SOlenoid Relay Circuit
C1223 - ABS Control System Malfunction
C1251 - Pump Motor is locked / open circuit in motor ground

 

[2001LC]

The brake pedal to floor, than working normal later. Means no brake booster pressure, then pressure returned. 8 out of 10 time this happens. This is strong indication, booster motor commutator has a dead spot on it. We'll often find, corrosion on brake control wires under boot at bottom of ABS unit. With both, it 98 out of a 100, dead spot.

The quest becomes, do I replace or rebuild the booster motor or replace the whole master assembly? 99 out of 100 it is best to replace the whole booster w/ mater assy. One and done as they say.

The P0504 would be one, to work to solve first. Not a code I've dealt with. Nor one that I'd "think" would prevent booster motor from getting power. But that I'm not sure of that. So investigate it first.

 

[tesq]

Thanks for the replies. The fluid has been flushed and is still clean. Definitely not low: if anything, a touch high but never overfilled and no evidence that there has been overflow.

I tried the 40-depression test procedure. Strangely, it didn't feel like the pedal feel changed much between press 1 and press 40. Around press 20 or so the pedal went further than before but I couldn't replicate. I also didn't note much of a change in fluid level. With key on the motor ran for around 30 seconds.

I also looked for corrosion under the boot on the ABS module: I didn't see much.

I'll probably have the car looked at by lexus: worth the diag cost. From there, looks like I'll be buying a new whole master assembly.

 

[tesq]

Following up in case others are interested, as I had some time to test some things out.

A correction to my initial post: I never cleared the ABS/VSC/TRAC codes, only the main OBD network ones (Engine/Transmission/Cruise Control), as I was using an MX reader and OBD Fusion.

This time, I cleared all the codes from all of the computers and did a couple things: first, I tested to make sure the failsafe was working by pressing the brake pedal around 10 times in rapid succession. The ABS, VSC, and TRAC lights illuminated with the buzzer sounding. Good to know that logic is working.

Second, I retested the 40-press thing, and found again that there did not seem to be much of a difference between the first and last press. Re-pressurizing again took around 32-35 seconds.

After these, I took the car on a short drive in an empty mall parking lot (after checking my ebrake trim). After some hard stops, I rechecked codes. Only one: P0504. Clearing that code and testing, it seems that it only triggers on brake presses where I do more than just lightly press the brake. I put in some more seat time and was unable to get any codes other than the P0504 to trigger.

So, that leads me to the following intermediate diagnosis:
-Based on the many presses required to have the brake pedal go to the floor, and the fact that the pressurizing motor comes on after every time I press the brake pedal, my accumulator is likely not holding pressure like it used to and is need of replacement.
-Based on the one time my booster motor failed to spin up at startup seems to indicate the commutator has a bare spot. I haven't been able to replicate this, so my guess is I'm in early stages (only at 91XXX miles).
-Together, those two conditions would explain the C1246 and the C1253 codes: after a few seconds of start-up, the booster motor is not running (C1253), and then the master cylinder pressure would've been below the threshold after a set number of seconds (C1246). C1223 is the general code, and C0278 has been noted in conjunction with C1253.
-For the P0504, it seems like the brake light switch is not functioning. I already have a replacement luckily, and will swap that out soon. My brake lights work, which is nice.

In the end, looks like I need to go buy a master cylinder assembly and some toyota fluid. I'll update if anything interesting happens.