Sounds like air in the ABS system. Really easy to let this happen with a master cylinder replacement.

Was the master cylinder replaced to try to fix this issue? Did the symptoms change at all after the change?

-Charlie

 

The MC was replaced in hopes of fixing the issue yes. And no the symptom did not get better after.

Would a bad ABS module have this symptom as well? Or it’s just air that needs to be bled out?

Thanks in advance.

 

The MC was replaced in hopes of fixing the issue yes.

So the problem was there prior to the MC replacement...
Was the fluid level okay when the old MC was first opened up?
Was any other brake work done prior to that?

Would a bad ABS module have this symptom as well?

Not normally.

Or it’s just air that needs to be bled out?

Likely this.
-----
Good luck.

 

When engine is off, a few pumps will get the pedal firm

Normal. The pedal firms up with the engine off after the booster loses its charge. This is unrelated to the sinking pedal problem.

As mentioned above, the pedal is sinking due to air trapped in the system.

If the air is in the ABS modulator, a bi-directional scanner will be needed to command activation of the ABS to purge the air.

 

I will try that and get back to you guys in a couple of days. Thanks.

 

I just bought the car, the most I know is prior to MC replaced, fluid was low and green.

My best guess is previous owner ran the old pads so low it sucked air into the system because when I saw it, the fluid was low and old but all 4 pads were brand new.

Any tips when I have the scanner hooked up to bleed ABS?

Should I activate and sit back, or hold pedal down, or open bleed screw at wheels?

Thanks.

 

A bad previous bleed could do it too - MC gets low, sucks in air on bleed and blammo.

The ABS system will have a purge 'cycle' that runs and flushes out the internal accumulators, etc. into the braking system, then you complete another bleed cycle at the wheels. I don't know the specifics of the Odyssey though.

On my 4Runner, there is no easily available tool to activate the ABS bleed cycle - so you just have to find a patch of dirt or ice and get ABS to activate and re-bleed if this problem happens, so it could be worse!

-Charlie

 

Thanks. Good to know.

I will attempt the ABS bleeding tomorrow and update you guys. Thanks again for all your inputs.

 

To make your life easier in the future. A pressure bleeder is 10x more effective and easier to use.
I bled 3 large bottles of fluid through my Ody when I bought it, and it stops on a dime. Don't bother with the catch bottle, just get some tygon hose and run it down into a pan or catch can.
With a pressure bleeder you can actually open multiple bleeder ports at once and thoroughly bleed the system faster than you can put it in the air without a lift. A lot of the difficulty with bleeding after a MC replacement is you're not getting the volume of fluid through that you need too while the ABS pump is running.

0101 - Round Universal Power Bleeder - Motive Products

 

To make your life easier in the future. A pressure bleeder is 10x more effective and easier to use.
I bled 3 large bottles of fluid through my Ody when I bought it, and it stops on a dime. Don't bother with the catch bottle, just get some tygon hose and run it down into a pan or catch can.
With a pressure bleeder you can actually open multiple bleeder ports at once and thoroughly bleed the system faster than you can put it in the air without a lift. A lot of the difficulty with bleeding after a MC replacement is you're not getting the volume of fluid through that you need too while the ABS pump is running.

0101 - Round Universal Power Bleeder - Motive Products

I see that model appears to have a cap thats like a MC cap. That fits a 4th gen? A 3rd gen too? They also mention an 0119 model for 20 bucks more with a more universal cap but looks too big for more modern hondas?

 

I do have that. That was gonna be another question when the time comes. Haha.

Maybe I’m using it wrong but every time I’ve used it, I don’t get stiff pedal feel. My procedure is, put correct cap/cover on. Pump to 15psi and see if it holds pressure. Then I fill the tank and re pump to 15psi to start bleeding.

The product saves me a lot of time but like I mentioned, I always get soft pedal after. Happens on different cars.

Please tell me tips or what I’m doing wrong. 😀

 

Bled the ABS. Did it 3 times.

Followed by suggested regular bleeding 2 people method starting FL, FR, RR, RL. I am still getting pedal sink.

It’s maybe 15-20% improvement but not night and day.

Any other ideas guys?

 

Are you fluid extracting the master cyl as dry as you can get it, then topping it off. Then using the bleeder setup?

Run the car for a minute. Then shut it off. Pop the vac line off the booster and it should hiss.
Run the car again then shut it off. Wait 5min then pop the vac line off. You should hear the same strong loss of vacuum.

 

Master cylinders need bench bled before installation.

 

The fluid is fresh and 3 days old. I completely flushed out the system when the MC was changed.

I follow the manufacture bench bleeding before installing MC. It said, fill up reservoir, open ports until continuous stream comes out, plug up port.

Then press on the MC no more than an inch until no bubbles comes up from reservoir. That’s what I did.

Would this be good enough?

 

I read from a few sources that a bad booster can cause sinking brake pedal as well.

I’ve been trying to understand how this is possible. Can someone confirm if this is possible, if so can you explain to me so I can understand.

Sources are saying a bad poppet valve can do this. Thanks.

 

I read from a few sources that a bad booster can cause sinking brake pedal as well

That's not my understanding, but I defer to others who may know of this symptom.

 

Ran the car couple of mins. Shut off. Waited 1 min. Pulled vacuum from booster, heard a loud whoosh.

Ran car again couple of mins. Shut off. Waited 5 mins. Pulled vacuum from booster, heard same loud whoosh.

Repeated this process waiting 15 mins. Same whoosh.

 

Sounds like the booster is holding.

 

Could it be ABS solenoid stuck open or close? Even if there is no codes on the ABS module?

I have a scanner that can access the life data of the solenoids. What should they say?

I don’t know if this yield any good information but when engine is off, pedal is hard with no sinking. Engine on it sinks, so I DC the vacuum and turned on the engine, it’s stiff.

 

but when engine is off, pedal is hard with no sinking. Engine on it sinks

I understand that the pedal sinks only when the engine is running. However, it may sink just the same with the engine stopped if only enough force were applied to the brake pedal. Normal force would be insufficient to apply the brakes, and grossly insufficient to compress any air in the system.

Try this:

• Drive to somewhere isolated and with lots of open space.
• Disconnect the booster vacuum line.
• Press the brake pedal a few times until it becomes hard.
• Drive the car slowly, about 20 MPH, with lots of open road ahead.
• Apply the brakes hard enough to get reasonable braking of the car. Use both feet if necessary.

Now you know how much extra force is needed to get the same braking performance.

Now with the engine off and a hard pedal, press on the brake pedal with the same force or more that you used in the motion test above. Hold for at least 15 seconds. The pedal should sink (obviously not normal, but consistent with the problem).

You will be no closer to finding the problem, but you will have resolved the question of why the pedal sinks only when the engine is running.

 

Hey guys. Update on the car.

I DC the brake lines from the MC and plugged it up. With engine ON and OFF, both times the pedal was rock solid. So I can eliminate MC and boosters as the issue.

I double checked for leaks from the MC, carefully inspecting each line out to the calipers. NO LEAK.

The only thing left that I can think of is the ABS module itself. I ordered a used one one eBay. $50. Installed, manual bled, ABS modulator bled, manual bled again. FINALLY my brake pedal is firm and is not sinking.

The ABS module did not have to be program, as long as its the same unit as your current and runs the same software. It was a straight plug and play, you just need a scanner that can clear ABS codes. When buying the used ABS module, I made sure the numbers on the round motor part with a bunch of dashes matches my own (57110-TK8-A020-M1).

I want to update as I found multiple threads online with the same issue but never provided a solution. I hope in the future if anyone is reading this, it will save you a lot of trial and error.

Thank you EVERYONE for your inputs.

 

Would a bad ABS module have this symptom as well? Or it’s just air that needs to be bled out?

 

ABS module is bad. One of the outlet/dump valve is stuck open OR its seal went bad. So when I press on the pedal, fluid is being re-directed to the acummulator, which sinks the pedal. When accumulator is full, pedal will stop sinking(which is 3/4 way down towards floor).

When I had air in the ABS system, you don’t feel brake pads engaging until low to the floor. When I scanner bled the module, I see air coming out, brake pads engagement is the very high up, but will still lose pressure and begin to sink.

 

We recently bought a 2015 odyssey with 125k on it. It had the same issue. Replaced MC and bled numerous times at honda dealership with no success. They called the abs module bad with no codes stored on it. The new module is as you all know, very expensive, especially with no way to verify an internal mechanical failure. We rolled the dice on a salvage unit for 60$ with scantool abs bleed and just as above , we have excellent brakes. We retained the old unit to have rebuilt and keep for a spare.