Very dangerous braking behavior after electronic brake booster module replacement

[Charles Bronson]

So about 2 1/2 weeks ago, Toyota replaced the electronic brake booster module on my wife's 2020 ORP. You can read about the fiasco of this replacement in this thread and post if you're interested:

https://www.toyota-4runner.org/3721817-post34.html

ABS, braking power low and drive start control malfunction lights

Fast forward to today. We take the 4runner to the next town over and are on the highway. The traffic starts coming to standstill fairly fast and I have to apply maybe 40% braking power. The truck slightly pulls right when I first squeezed the brakes. My wife then says "Did you notice that? The truck has been doing that for a while under harder braking". I didn't think any of it as I figured I just braked hard and caught a bit of road crown and it slightly pushed the truck right fractionally as I came off the crown. I told my wife I'd look at it when we got home.

I unload the family and take the truck to a vacant industrial park. I'm going about 45mph and I push the brakes to maybe 60-70% braking. The front tires immediately start locking up (no ABS intervention), the entire truck starts rotating on its axis starting heading to the right side of the lane/shoulder as the brakes lock up, then the ABS finally starts cycling, which then oddly makes the truck pull even harder to the right, then all of sudden, it feels like I have no braking power at all even though I'm still holding the pedal down, then they start working again a fraction of a second later. I damn near went off the road as this all happened in the matter of a couple of seconds.

I then tested it again, but with less braking power (~50%) and I could hear the front right wheel locking up (tire screeching) and the truck starting to rotate and begin going right. I could reproduce this braking behavior over and over again.

I autocross/road race and never in my life have I felt an ABS or non-ABS braking system exhibit such erratic behavior. It's like the brake proportioning on way off on each corner. It was rather frightening, especially when the truck started to act like a Mustang leaving a car show and aim right for the curb along with the brakes momentarily turning off (is that even possible?). The truck felt totally out of control.

I immediately went home and told my wife that we needed to take the truck in first thing on Monday and that she needed to stay off the highways for the time being.

Does anyone have a clue about how the braking system works on the 5th gen? I don't see a vacuum brake booster. It looks to all be electronically/hydraulically controlled and actuated. Is there some sort of programming needed for the installation of electronic brake booster module? There are no codes being thrown. When the ABS does come on, the ABS light flickers like you'd expect. We do know that when the tech replaced the electronic brake booster module, they did have to bleed the brakes and when they did it the first time, they told us "something isn't right" and they held on to it another day. We have no idea what wasn't right. I assumed he was have trouble getting air out of the brake lines. I don't think there's air in the brake lines now because the pedal feels completely fine and no spongy.

I will add that the threshold braking/behavior was completely fine prior to them replacing electronic brake booster module.

This is so frustrating to say the least.

 

[Jetboy]

I'm not an expert on the abs algorithm beyond the basics. At a high level the brake system uses electronic boost via a hydraulic pump and an accumulator integrated into the master cylinder. So no vacuum system. The MC can adjust pressure internally. Each wheel brake can be actuated or cut by the master cylinder independently.

The pressure you feel in the pedal is all the result of the software. It could be any feel the engineers wanted. And the system can ramp up from zero to fully locked up with or without driver input. And it can also cut pressure to each brake. I don't think it can vary pressure in the sense that it can't ease off the pressure to one wheel, it's pump pressure or zero in pulses.

The circuits as I understand it (this may be wrong) have a bypass design and a seal failure could bypass the circuit back to the reservoir. I'm not sure if an internal seal or solenoid failure could increase pressure to a single tire.

The only other thing I know is that brake pressure boost varies based on the ECU software. I don't know how it chooses what level of boost. I do know if you very quickly move from throttle to brake it spikes the boost pressure and it brakes very hard.

Wheel speed is taken from hall effect sensors. A partially failing sensor could cause issues.

That's about all I think I know. There's been a few reports of brake issues where drivers feel like there's no brakes on the first push. Not sure if they decided it was electric or mechanical problem.

 

[Something_Awesome]

Is the 4Runner with this issue a 2022? I have heard of brake-related issues with the 4Runner, but that most of the 4Runners that had the issue were 2016 and earlier. Though its possible that the older ones are having the problem simply because they have more wear and tear on them.

I read your posts, and given the milage you referenced, I am guessing a 2022? In this case, should Toyota not be aware of this? Call corporate?

If this can't get fixed, can't you lemon the car? A car with braking issue has no business being on the road. I feel like you should be able to lemon the car because it is still under warranty.

EDIT: Never mind, I see it's a 2020. Still under warranty though. If they can't fix it on Monday, LEMON it. I believe whatever the threshold is that triggers a Lemon, that threshold is reduced when the issue is dangerous. I think this means you could potentially get a refund?

 

[BadTrainDriver]

Is the 4Runner with this issue a 2022? I have heard of brake-related issues with the 4Runner, but that most of the 4Runners that had the issue were 2016 and earlier. Though its possible that the older ones are having the problem simply because they have more wear and tear on them.

I read your posts, and given the milage you referenced, I am guessing a 2022? In this case, should Toyota not be aware of this? Call corporate?

If this can't get fixed, can't you lemon the car? A car with braking issue has no business being on the road. I feel like you should be able to lemon the car because it is still under warranty.

EDIT: Never mind, I see it's a 2020. Still under warranty though. If they can't fix it on Monday, LEMON it. I believe whatever the threshold is that triggers a Lemon, that threshold is reduced when the issue is dangerous. I think this means you could potentially get a refund?

Depending on where OP is located, this may not be an option. I live in Ohio, and our Lemon Law is 12months, 18k miles.

 

[Something_Awesome]

OP, if you could do this all over again, would you have not allowed the dealer to replace the electronic brake booster module? By the looks of it, it seems like the issue got worse after that?

I personally go to another dealer when I get a vibe that the guys at a specific dealer are not competent. All it takes is for you to find one guy that knows what’s going on. There is a dealer that is an hour away from me that I would go to first if ever some serious issue arose. It’s a huge dealer and they are known to have a great and experienced service people. The guy servicing your 4runner not only seems stumped, but not interested in investigating your issue further. Perhaps it's time to go elsewhere. Dare I say a reputable independent mechanic?

Man, this really sucks. I feel for you. Keep us updated.

 

[Jetboy]

This is how the MC is designed. Everything you see here is integrated into the master cylinder except the 4 brake calipers on the lowest row. If you need some guidance on which valves open or close under what conditions I'm happy to try to explain how and when each valve would open and close. If you look closely you can see the valves in the diagram that are normally open are also open visually where the little pentagon looking representation of the valve seal is open vs closed.

The first row of valves below the MC are the set that determines whether the driver or the ECU is going to control the brakes. The second row down are normally open and can close to cut pressure to individual brakes. The third row down are normally closed and when open will bypass each individual brake and return the fluid to the reservoir. In order to operate an ABS wheel you would close the valve in the second row for the channel and open the valve in the third row simultaneously. If you just block the channel the brake caliper on that channel would remain locked up. So you need the return valve to open to release pressure. But if you don't first block that channel, the system would all lose pressure through the one open return channel.

What that means is that it's possible in your case that something like one of the valves that should be closing a channel isn't closing it. And so when the pressure relief valve that should open momentarily after the channel is blocked does so, the system drops pressure across the entire system, then it triggers the pressure sensor to ramp up pressure by running the pump and because the system has long narrow tubes, the pressure drop and recovery would propagate unevenly through the system and you'd have a pull to one side potentially. This could be more pronounced if you had a valve that was delayed in closing or opening or possibly not fully closing or opening. That might cause a short term pressure drop followed by a spike in pressure. Lots of potential combinations of stuff that could cause some unusual behavior if it's not all working correctly.

 

[CutthroatSlam]

Seems like a proportion valve issue. Should be able to get that fixed.

 

[BlackWorksInc]

Seems like a proportion valve issue. Should be able to get that fixed.

I don't think Toyota has used a proportioning valve since we started using our more advanced ABS actuators, I want to say in early 2000's? It's all done through the ABS actuator assembly these days.

In regards to the OP's concern, it sounds like something possibly didn't get bled out right. I suppose it is possible that the unit could be DoA, but that's beyond what we can determine online for you.

 

[catrains]

I unload the family and take the truck to a vacant industrial park. I'm going about 45mph and I push the brakes to maybe 60-70% braking. The front tires immediately start locking up (no ABS intervention), the entire truck starts rotating on its axis starting heading to the right side of the lane/shoulder as the brakes lock up, then the ABS finally starts cycling, which then oddly makes the truck pull even harder to the right, then all of sudden, it feels like I have no braking power at all even though I'm still holding the pedal down, then they start working again a fraction of a second later. I damn near went off the road as this all happened in the matter of a couple of seconds.

I then tested it again, but with less braking power (~50%) and I could hear the front right wheel locking up (tire screeching) and the truck starting to rotate and begin going right. I could reproduce this braking behavior over and over again.

.

the front brakes work good .. now the rear brakes did have a low braking issue .. front brakes lock up then the PCM create a on/off braking...
you have to bleed the rear brakes calipers .. use a plastic clear tubing put a glass bottle with fluid in it..... push the pedal down keep the stick to keep it down then bleed the right rear caliper .. do it a few times with no air bubbles in the plastic tube... then do the driver side rear caliper ... if the rear brakes have no air in the fluid, then the runner works correctly...

 

[Charles Bronson]

OP, if you could do this all over again, would you have not allowed the dealer to replace the electronic brake booster module? By the looks of it, it seems like the issue got worse after that?

Yes, we totally regret having them do the work. The module wasn't the problem but the tech thought it was so he ordered the part. The service advisor said they don't get paid unless they install the part so out of the goodness of our heart, we let them do it and here we are.

Thank you everyone for posting the tech specs of the braking system.

I went out and retested the truck a few minutes ago and it still has the same issue. The truck goes in tomorrow and I highly doubt we'll get it back the same day. I'm guessing 2 to 40 days depending on what it needs.

I'll keep the group posted.

 

[Charles Bronson]

Is the 4Runner with this issue a 2022? I have heard of brake-related issues with the 4Runner, but that most of the 4Runners that had the issue were 2016 and earlier. Though its possible that the older ones are having the problem simply because they have more wear and tear on them.

I read your posts, and given the milage you referenced, I am guessing a 2022? In this case, should Toyota not be aware of this? Call corporate?

If this can't get fixed, can't you lemon the car? A car with braking issue has no business being on the road. I feel like you should be able to lemon the car because it is still under warranty.

EDIT: Never mind, I see it's a 2020. Still under warranty though. If they can't fix it on Monday, LEMON it. I believe whatever the threshold is that triggers a Lemon, that threshold is reduced when the issue is dangerous. I think this means you could potentially get a refund?

We're outside the Kansas lemon law window. I'll be curious to see what the issue is. Depending on what found (part failure or a tech mistake) will determine how we may proceed with the dealer and Toyota corporate.

The whole experience has been really bad and the fact that my wife and kids have been traveling all around the city for 2.5 weeks with such a dangerous issue is really bothersome. There is no doubt in my mind that a fairly hard stop at highway speed would take the truck off the road or into the lane to the right. It's uncontrollable even with the steering wheel aimed straight.

 

[BlackWorksInc]

Yes, we totally regret having them do the work. The module wasn't the problem but the tech thought it was so he ordered the part. The service advisor said they don't get paid unless they install the part so out of the goodness of our heart, we let them do it and here we are.

Thank you everyone for posting the tech specs of the braking system.

I went out and retested the truck a few minutes ago and it still has the same issue. The truck goes in tomorrow and I highly doubt we'll get it back the same day. I'm guessing 2 to 40 days depending on what it needs.

I'll keep the group posted.

I skimmed your prior thread (apologies, didn't have time or mental bandwidth to fully study it tonight) and I'm guessing TAS likely advised them to replace the booster unit. Given the odd symptoms and some prior case history, that seems like something TAS would do (have run into a couple weird premature failures/inconsistent operation of the ABS units in a couple vehicles before; very rare, but it has happened). Honestly, I'm not entirely sure what else would be left to address in the system that would contribute to disabled ABS/VSC/TRAC function without DTCs that gave you a rough direction to follow. The booster unit is basically everything, module, solenoids, valves, and master cylinder; the only things left in the braking system are just lines, caliper, brake pedal, and stop light switch.

I still think the new unit didn't get bled properly, but I am not sure about your original concern; that's gonna need a different night for me to really dig into it as it's piqued my curiosity now. But yeah, seems like you have not had a good time with this issue and some of the oofs you posted in the previous thread make me wince a little. I hope things get resolved soon for you and your family!

 

[Charles Bronson]

I skimmed your prior thread (apologies, didn't have time or mental bandwidth to fully study it tonight) and I'm guessing TAS likely advised them to replace the booster unit. Given the odd symptoms and some prior case history, that seems like something TAS would do (have run into a couple weird premature failures/inconsistent operation of the ABS units in a couple vehicles before; very rare, but it has happened). Honestly, I'm not entirely sure what else would be left to address in the system that would contribute to disabled ABS/VSC/TRAC function without DTCs that gave you a rough direction to follow. The booster unit is basically everything, module, solenoids, valves, and master cylinder; the only things left in the braking system are just lines, caliper, brake pedal, and stop light switch.

I still think the new unit didn't get bled properly, but I am not sure about your original concern; that's gonna need a different night for me to really dig into it as it's piqued my curiosity now. But yeah, seems like you have not had a good time with this issue and some of the oofs you posted in the previous thread make me wince a little. I hope things get resolved soon for you and your family!

Thank you for the input. Much appreciated. Are you a Toyota technician?

The truck was dropped off this afternoon and around 530pm the service advisor left my wife a message that they were able to reproduce the issue. Im relieved to hear that. They said the truck is needing to undergo a number of braking tests and procedures. We'll see where this goes.

 

[dflowerz]

Glad that dealer could reproduce the issue. That's half the battle. Hope they get if fixed quickly.

 

[DougR]

... the tech thought (a module) was (faulty) so he ordered the part. The service advisor said they don't get paid unless they install the part ...

So, the tech thinks you need a module and the service advisor doesn't get a commission unless a part is installed.

At this point, it's OK to say to the advisor "It appears your offer to repair is a guess." Then ask who's money are they guessing with, yours or theirs? Ask them to give you your old part in case their guess doesn't fix your symptom. Ask if their guess doesn't work, who pays the diagnostic fee, labor to install a new part, and labor to reinstall the old part?

When the symptom is not resolved with a new part, the shop and the customer may share some risk when the offer to repair is a guess. It is reasonable for the shop to reinstall your old part, while you receive a refund on the cost of a new part. You agree to pay labor to have your old part reinstalled and the shop agrees to pay the diagnostic fee and labor they charged to install a new part.

 

[Hadelson]

Yes, we totally regret having them do the work. The module wasn't the problem but the tech thought it was so he ordered the part. The service advisor said they don't get paid unless they install the part so out of the goodness of our heart, we let them do it and here we are.

Thank you everyone for posting the tech specs of the braking system.

I went out and retested the truck a few minutes ago and it still has the same issue. The truck goes in tomorrow and I highly doubt we'll get it back the same day. I'm guessing 2 to 40 days depending on what it needs.

I'll keep the group posted.

I had a 17 TRD Pro and had a total brake system failure. Details buried somewhere on the forum. Took over 30 days for Toyota to diagnose and fix. At first, they wanted me to come take the truck as they could not find the issue. Long story short, they sent a senior tech in and hooked the truck up to a computer and we drove it for about 50 miles. They then ask me approximate Date/Time of the failure. From here, they pulled codes that showed the failure of the system. They authorized and completed a full system replacement. No other issues with the T4R

 

[BlackWorksInc]

So, the tech thinks you need a module and the service advisor doesn't get a commission unless a part is installed.

At this point, it's OK to say to the advisor "It appears your offer to repair is a guess." Then ask who's money are they guessing with, yours or theirs? Ask them to give you your old part in case their guess doesn't fix your symptom. Ask if their guess doesn't work, who pays the diagnostic fee, labor to install a new part, and labor to reinstall the old part?

When the symptom is not resolved with a new part, the shop and the customer may share some risk when the offer to repair is a guess. It is reasonable for the shop to reinstall your old part, while you receive a refund on the cost of a new part. You agree to pay labor to have your old part reinstalled and the shop agrees to pay the diagnostic fee and labor they charged to install a new part.

This is all under warranty as far as I can tell from the OP's posts (correct me if I'm wrong), the part will likely be tagged and returned to Toyota due to the situation and cost of the repair. As for them "getting paid," that's a more complicated answer that has to do with the bureaucracy and bullshit in dealing with warranty work; but the long and short of it is warranty doesn't pay diagnosis time, only repair time (and most warranty labor is already barely break even if you're lucky.) So any time you spent diagnosing the vehicle, having to call TAS or your FTS, doing lots of tests or pedantic testing because the above needs it for the case file, etc
... the technician and the dealership is not getting reimbursed for until something is replaced (maybe if you're lucky you can attach some Z-Time to the op code, but usually they balk at that.).

 

[Charles Bronson]

April 13, 2022 Update

The braking issue is fixed and the truck returned to us last night. I've tested the truck numerous times and everything works fine. The work was done under warranty.

The issue was related to a programming/coding glitch with the newly installed electronic brake booster module. When this module is installed, the tech is to perform a "zero point calibration" of the ABS unit, steering angle sensor, yaw rate sensor, and accelerator sensor. Apparently this is a rare thing to do with later model 4Runners as they aren't often in for repairs.

When the module was installed, the tech performed the calibration which takes a while. The calibration shut-off thus the tech assumed the calibration took and the truck was returned to us. It turns out that the calibration did not take and simply timed out thus is the reason why the truck behaved so wonky under hard braking. It makes total sense as to why the brakes seemed to be working independently against each other and the truck rotating on its axis all the while the steering wheel straight.

According to the service advisor, when the tech test drove our truck, he nearly lost control during heavy braking. The service advisor even put in an email to me that the tech drove the truck and the braking is "NOT" right at all. I'm glad I wrote a letter to the tech describing the issue in detail and to make sure that the tech understood to have adequate space to the right as that's where the truck will go quite violently if you're really hard on the brakes.

Once back in the shop, the tech ran a bunch of tests and he kept coming back to the zero point calibration. He tried the calibration multiple times and it would never indicate to him that it was done. It just timed out. To make sure this was correct, he called TAS and had an engineer walk him through the process. Turns out the current written procedure is missing a crucial step thus wasn't allowing the calibration to take. Once they figured it out, the calibration took. The procedure has been updated because of this.

It's rather scary how technology can work against you and what is designed to save lives could actually take them away if it's not timed correctly :wow:

 

[BlackWorksInc]

April 13, 2022 Update

The braking issue is fixed and the truck returned to us last night. I've tested the truck numerous times and everything works fine. The work was done under warranty.

The issue was related to a programming/coding glitch with the newly installed electronic brake booster module. When this module is installed, the tech is to perform a "zero point calibration" of the ABS unit, steering angle sensor, yaw rate sensor, and accelerator sensor. Apparently this is a rare thing to do with later model 4Runners as they aren't often in for repairs.

When the module was installed, the tech performed the calibration which takes a while. The calibration shut-off thus the tech assumed the calibration took and the truck was returned to us. It turns out that the calibration did not take and simply timed out thus is the reason why the truck behaved so wonky under hard braking. It makes total sense as to why the brakes seemed to be working independently against each other and the truck rotating on its axis all the while the steering wheel straight.

According to the service advisor, when the tech test drove our truck, he nearly lost control during heavy braking. The service advisor even put in an email to me that the tech drove the truck and the braking is "NOT" right at all. I'm glad I wrote a letter to the tech describing the issue in detail and to make sure that the tech understood to have adequate space to the right as that's where the truck will go quite violently if you're really hard on the brakes.

Once back in the shop, the tech ran a bunch of tests and he kept coming back to the zero point calibration. He tried the calibration multiple times and it would never indicate to him that it was done. It just timed out. To make sure this was correct, he called TAS and had an engineer walk him through the process. Turns out the current written procedure is missing a crucial step thus wasn't allowing the calibration to take. Once they figured it out, the calibration took. The procedure has been updated because of this.

It's rather scary how technology can work against you and what is designed to save lives could actually take them away if it's not timed correctly :wow:

My guess is that he got tripped up by the parking brake step, I had a similar fiasco on an older Camry Hybrid that I did a unit on. Would not calibrate the ZPC and Linear Solenoid Valve despite doing everything the book required for replacement. Eventually figured out that you needed to disengage the parking brake after a specified part of the scan tool n process (was a guess based on context of the steps after that point, the FSM or scan tool prompts never mentioned to actually disengage the parking brake at that step).

There are multiple options with the scan tool when replacing components like the ABS Unit. Most of them are fairly clear in what you need to do step by step with on screen prompts (the full process basically bleeds the unit, pressurizes it, and depressurizes, repeating these steps a few times, then it will play with its solenoids and sensors a bit, pressurize itself, and then depressurize itself a few more times, followed by a self calibration of some final sensors; then after all that the technician goes and does the ZPC relearn for Taw arate and such), but sometimes they aren't clear when a calibration doesn't take or *why* it doesn't take. I'm a bit surprised that it didn't immediately set a ZPC error that he couldn't clear before test driving the vehicle. Usually that's a sign that something didn't take correctly as the Zero Point Calibration of the Yaw Rate and Acceleration sensor is one of the last commanded calibrations on most Toyota/Lexus ABS systems (steering angle ZPC is usually handled automatically by driving in a straight line above 20mph for a short while).

It's possibly that technician hasn't done a whole lot of ABS Unit replacements and must have missed the RAV4 and Prius recalls years ago. That being said, it does sound like a weird glitch; like I said, usually if the new unit calibration process fails/acts up it sets at least one or two DTCs that you can't clear or calibrate away until you start the whole process from scratch. So that certainly sounds like a weird anomaly based on my experience.

In any case I'm glad everything was fixed and no one was hurt in the process!

 

[Charles Bronson]

My guess is that he got tripped up by the parking brake step, I had a similar fiasco on an older Camry Hybrid that I did a unit on. Would not calibrate the ZPC and Linear Solenoid Valve despite doing everything the book required for replacement. Eventually figured out that you needed to disengage the parking brake after a specified part of the scan tool n process (was a guess based on context of the steps after that point, the FSM or scan tool prompts never mentioned to actually disengage the parking brake at that step).

There are multiple options with the scan tool when replacing components like the ABS Unit. Most of them are fairly clear in what you need to do step by step with on screen prompts (the full process basically bleeds the unit, pressurizes it, and depressurizes, repeating these steps a few times, then it will play with its solenoids and sensors a bit, pressurize itself, and then depressurize itself a few more times, followed by a self calibration of some final sensors; then after all that the technician goes and does the ZPC relearn for Taw arate and such), but sometimes they aren't clear when a calibration doesn't take or *why* it doesn't take. I'm a bit surprised that it didn't immediately set a ZPC error that he couldn't clear before test driving the vehicle. Usually that's a sign that something didn't take correctly as the Zero Point Calibration of the Yaw Rate and Acceleration sensor is one of the last commanded calibrations on most Toyota/Lexus ABS systems (steering angle ZPC is usually handled automatically by driving in a straight line above 20mph for a short while).

It's possibly that technician hasn't done a whole lot of ABS Unit replacements and must have missed the RAV4 and Prius recalls years ago. That being said, it does sound like a weird glitch; like I said, usually if the new unit calibration process fails/acts up it sets at least one or two DTCs that you can't clear or calibrate away until you start the whole process from scratch. So that certainly sounds like a weird anomaly based on my experience.

In any case I'm glad everything was fixed and no one was hurt in the process!

Thank you for all the information. I wish you were in Kansas City!