Possible VSA Failure?

[1sloazfk8]

Has anyone had their VSA fail and can report the symptoms they experienced.

Currently I have a soft pedal after a track day but all components are new, had dealer look at it and replaced the brake master cylinder which gave a slight improvement but there is still some softness on initial application. All checks show system is working fine according to the Honda repair directions and the VSA is the last piece that hasn't been touched. Have already gone through multiple fluid bleeds and caliper repair as well.

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[Los’fk8]

Hey there. Maybe some help (maybe not) but there are instances in other previous model Acuras/Hondas that had issues with VSA’s malfunctioning after some sort of impact (pothole, curb, etc). It might be that. Also, something that im sure you’ve checked already, but might be an issue is a tear in the brake line. I know they are pretty rare, but considering you were tracking the car, it could be possible? Soft pedal generally means air in the system or loss of hydro pressure, but I guess if all lf those boxes are checked, it would have to be some sort of electrical malfunction…

 

[1sloazfk8]

Hey there. Maybe some help (maybe not) but there are instances in other previous model Acuras/Hondas that had issues with VSA’s malfunctioning after some sort of impact (pothole, curb, etc). It might be that. Also, something that im sure you’ve checked already, but might be an issue is a tear in the brake line. I know they are pretty rare, but considering you were tracking the car, it could be possible? Soft pedal generally means air in the system or loss of hydro pressure, but I guess if all lf those boxes are checked, it would have to be some sort of electrical malfunction…

Everything is physically fine, I still have air in the system as a possible cause, but with how many times this has been bled between a caliper refresh and steel braided lines along with dealer doing the master cylinder this is the last part of the equation to rule out.

Hydraulic pressure holds once built, booster checks are all good, just dealing with an initial 30-40% pedal travel before any tangible feedback is felt. The only other symptom is that I can hear my shims "crunching" on some stops during road tests and a possible unrelated clicking on brake release where pressure is released and needs rebuilt. But neither are consistent.

 

[tacthecat]

Sounds like air in the VSA/ABS system - did you and everyone else who worked on the brake system follow the Honda manual (chap. 27) procedure requiring bleeding the system then setting and releasing the parking brake 5 times and then re-bleed the entire system (2 compelete bleeds with the special procedure in the middle)?

 

[1sloazfk8]

Sounds like air in the VSA/ABS system - did your follow the Honda manual (chap. 27) procedure requiring bleeding the system then setting and releasing the parking brake 5 times and then re-bleed the entire system?

Yep, that has been done a few times, will see what happens tomorrow when I take it back to the shop and we try a couple different bleeding methods again.

 

[keller]

This is interesting. It seems you did all the right checks. What is your theory regarding the VSA? You can just disconnect the VSA electric connector and do a quick test. You'll get a ton of DTCs but should be able to test it.

This doesn't seem like air in the system, as it would show a linear feel on the brake pedal. Have you visually inspected your calipers and lines when building and releasing pressure? Not while bleeding and with the booster assist.

 

[1sloazfk8]

VSA is the only component not touched or changed, pedal was improved post master cylinder swap and feels normal once pressure is felt after about 20-30% application and even a light load will not allow parking brake release. Calipers didn't look or seek damaged on inspection during seal replacement, currently back at a shop going through a rebleed after driving another couple of days

Beyond that I have no other ideas to look at, my thought is VSA is bleeding pressure due to being faulty.

 

[AlphaDigital]

Interested to see what the root cause of this is if you figure it out!

 

[1sloazfk8]

Picked up the car today, shop got some more air out of the lines which is good, but pedal feel is still the same. Unsure if it happened before but I did notice that the pedal did seem to sink to the floor while running once I come to a stop.

Makes me wonder if the booster went out as well but that seems unlikely, I know the check valve is working since it makes noise when you unplug the hose. Will see if I can get a line to Honda engineers or find a solid master tech lol.

 

[keller]

I did notice that the pedal did seem to sink to the floor while running once I come to a stop.

Ohh damn, so it's getting worse. A faulty booster doesn't make the pedal sink. In fact, it would barely move.

Our cars show the brake pressure in the instrument panel, which is a huge help to quickly test for air or moisture in fluid. You could try that.

It's hard to understand how you still have air inside your brake lines after this many bleeding procedures. If this was due to a faulty line, you should see fluid leaking whenever you build pressure.

Beyond that I have no other ideas to look at, my thought is VSA is bleeding pressure due to being faulty.

Bleeding pressure as in leaking fluid? Well you'd notice the fluid level quickly dropping just from pumping your pedal.

FYI below is the VSA internal hydraulic circuit. You can completely deactivate it by just disconnecting the electrical connector.

 

[1sloazfk8]

Ohh damn, so it's getting worse. A faulty booster doesn't make the pedal sink. In fact, it would barely move.

Our cars show the brake pressure in the instrument gauge, which is a huge help to quickly test for air or moisture in fluid. You could try that.

It's hard to understand how you still have air inside your brake lines after this many bleeding procedures. If this was due to a faulty line, you should see fluid leaking whenever you build pressure.



Bleeding pressure as in leaking fluid? Well you'd notice the fluid level quickly dropping just from pumping your pedal.

FYI below is the VSA internal hydraulic circuit. You can completely deactivate it by just disconnecting the electrical connector.

Bleeding as an internal issue, fluid level is not changing and all hydraulic lines are good. Everything at this point is new on the car except the booster or VSA module. I feel I am just missing something so simple at this point and it is a bit frustrating this happened a month before Super Lap Battle as well.

I may try unplugging the VSA to see what happens, who knows maybe "turning it off and on again" is the fix. I have been looking at the pressure gauge on the dash and I don't see much pressure built up initailly as it stays around 1-2 and peaks at 4, after a few pumps it holds at 10 or so. Only other thing I can check and going out on a limb on is the vacuum pump, but that is super unlikely in my opinion.

May also see if Flashpro tracks brake pedal position and pressure, to see how it correlates.

 

[keller]

I don't see much pressure built up initailly as it stays around 1-2 and peaks at 4, after a few pumps it holds at 10 or so

It peaks at 4 at what pedal displacement? At the floor? You can't make 15 with maximum force without pumping it?

A bad vacuum pump has the same symptom as a bad booster: heavy pedal, instead of a soft pedal.

 

[1sloazfk8]

It peaks at 4 at what pedal displacement? At the floor? You can't make 15 with maximum force without pumping it?

A bad vacuum pump has the same symptom as a bad booster: heavy pedal, instead of a soft pedal.

At about 20-30% application I start to see a pressure of 1-2 on the gauge and feel it in the pedal, halfway is about where it starts to feel normal and can see 4 or higher until it gets close to the floor and it will go up around 10. But pumping the pedal even while running increases that earlier. I will datalog some stuff in the morning to see what I can find.

I have also thought of calipers and wondering, despite new piston seals, maybe there is an issue there due to the amount of times they got hot. But again that is reaching for something way out there.

 

[DRUSA]

Try this, per the FSM:

Brake Booster Function Test

1. Turn the vehicle to the OFF (LOCK) mode, press the brake pedal several times to deplete the vacuum reservoir, then press the brake pedal hard and hold it for 15 seconds. If the brake pedal sinks, either the master cylinder is bypassing internally or the brake system is leaking. Inspect the brake hoses and lines. 2. Start the engine with the brake pedal pressed. If the brake pedal sinks slightly, the vacuum booster is operating normally. If the brake pedal height does not change, do the brake system test.

2.	Brake Booster Leak - Test

1. Press the brake pedal with the engine running, then turn the vehicle to the OFF (LOCK) mode. The brake pedal height should not change while pressed for 30 seconds. If the pedal height rises, go to step 6. If it does not rise, go to step 2. 2. Start the engine, and let it idle for 30 seconds. Turn the vehicle to the OFF (LOCK) mode, and wait 30 seconds. Press the brake pedal several times using normal pressure. When the pedal is first pressed, it should be low. On consecutive applications, the pedal height should gradually rise. If it rises, the booster is OK. If it does not rise, go to step 3. 3. Disconnect the brake booster vacuum hose (A) at the booster. The check valve (B) is built into the hose. NOTE: If the check valve is faulty, replace the brake booster vacuum hose and the check valve as an assembly. 4. Start the engine, and let it idle. There should be vacuum available. If no vacuum is available, the check valve is not working properly. Replace the brake booster vacuum hose and the check valve as an assembly, and retest. If vacuum is found, go to step 5. 5. Turn the vehicle to the OFF (LOCK) mode, reconnect the vacuum hose to the brake booster. 6. Start the engine, and then pinch the brake booster vacuum hose between the check valve and the booster. 7. Turn the vehicle to the OFF (LOCK) mode, and wait 30 seconds. Press the brake pedal several times using normal pressure. When the pedal is first pressed, it should be low. On consecutive applications, the pedal height should gradually rise. If the pedal position does not change, inspect the seal between the master cylinder and the booster. If the seal is OK, replace the brake booster. If the pedal position changes, replace the brake booster vacuum hose and the check valve as an assembly.

 

[DRUSA]

I've never seen a VSA module "leak internally" like how you are describing. They pretty much just modulate braking when requested to do so, old style ABS stuff. If you are feeling a spongy pedal that is either air in the system, a junk master cylinder or booster. A junk master cylinder will slowly let the pedal sink with the car off with the light weight of your foot barely resting on the pedal.

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