2009 Toyota Sienna Fading Brake Pedal

Steve Owner/Technician Spokane, Washington Posted   Latest   Edited  
Question
Braking
2009 Toyota Sienna CE 3.5L (2GRFE) 5-spd (U151F)—5TDZK23C09S272755

Car stops normal, but sitting at a light the pedal will slowly go to the floor. Bled system normally & with scanner and still same problem. Also tried dinamite brake pedal in park in shop & pedal goes instantly to the floor. New rear calipers as one had a broken bleeder. Problem was there prior to calipers on rear.

Have bled master cylinder bleeder according to service manual.

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Joseph Technician
Calgary, Alberta
Joseph Default
 

Not to sound like a smart ass, but it sounds like a bypassing master cylinder to me. Usually a quick and hard brake stop will be fine, but a slow and gentle brake application will let the pedal slowly sink to the floor. I've seen it many many times. Oh, and obviously make sure you aren't losing fluid and don't have a small leak somewhere.

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James Owner/Technician
Santa Barbara, California
James Default
 

What Joseph said is where I went with these symptoms. Sounds like a bad master to me. Thanks

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Randy Diagnostician
Glendora, California
Randy Default
 

True butt are you sure . Have done a lot of diag from other shops that replaced master and same problem . Im just saying this is my test .

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Randy Diagnostician
Glendora, California
Randy Default
 

Pinch all four brake line hoses and see what happens . If still no good it is upstream . Block master cylinder lines and check if problem is gone it is the abs unit is bad. I have done a lot of these

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Rob Owner/Technician
Nanaimo, British Columbia
Rob Default
 

Good advice so far but I'm not a fan of pinching off flex lines as they are not intended to be crushed and you may create another problem. This may help isolate the problem amazon​.​com/Thexton-803P-U… If the master cylinder passes the light pedal application with the plugs installed then you most likely have a bad ABS unit, this of course assuming that the rest of the braking…

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Thomas Instructor
Jacksonville , Florida
Thomas Default
 

Make sure you are following the OEM bleeding procedure. Something the bleeding Sequence is different From what we used in the past. Good luck

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Randy Diagnostician
Glendora, California
Randy Default
 

True with pinching lines . But are you going to disconnect every brake hose and cap it off . No if you donot over crimp hose you will not have a problem . Been doing this test for over 40 years . And if you do over crimp hose what is going to happen . That line will not relive pressure and brake will not release .

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James Owner/Technician
Santa Barbara, California
James Default
 

I agree with your crimp test, and suppose it is another check to avoid throwing parts at this. I have just had some problems pinching lines to failure, then adding a line or lines to a master cylinder failure . I think it’s a 50/50 deal, damned if you do damned if you don’t. It’s a gamble. cheers

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Randy Diagnostician
Glendora, California
Randy Default
 

Google f350 bad abs unit . Just one of many

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Anura Educator
Auckland, New Zealand
Anura Default
 

Very much positive bad seals in master, replace mate.

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Randy Diagnostician
Glendora, California
Randy Default
 

Are you sure ???? Car comes in miss fire on #3 are you going to shoot parts cannon at it ?? And replace coil . Brakes are more complex today. Check system as if it was a mis fire . Use more thought than it sounds like and replace part . Charge diag do not assume. First three letters in this word is ass.......... . Do not assume be sure

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Luis Technician
Lake Forest, California
Luis Default
 

Pressure Bleed it. In correct sequence, then wet the outside floor with water hose. Open space where you can do some panic stops to activate abs at Least 4 times then test drive and see if pedal gets better

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George Owner/Technician
Skagway, Alaska
George Default
 

When you pull the master cylinder off look behind it and see if there is any fluid leaks. It sounds like a bad master cylinder. That is the symptoms that I always look for with one of these.

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Bill Owner/Technician
Jackson, Michigan
Bill Default
 

I have seen rusted backing plates /shims causing this on some Toyota's as well as sticking slide pins. It's worth pulling off the front calipers and checking if you have not been there

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David Mechanic
Stockport, United Kingdom
David Default
 

Hi Steve, I use a Gunsons Ezibleed on the tough ones , cheep and a bit flimsy but works . It connects to the tyre valve and uses the air pressure to push fluid through the system , give it a google only around £ 20 hear in the UK . The tip about clamping the flexi hoses is a good one and aids diagnosis . Good luck and regards Dave T...

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Hollis Technician
Boulder, Colorado
Hollis Default
 

Sounds like a by-passing master cylinder... Things to consider, age, mileage, how many times the pedal has gone to the floor (meaning, debris from wear in the MC bore, each time it may pick up a little more compromising the piston seal) As Bill K. mentioned, sticking, seized caliper slide pins. Other considerations, loose / worn wheel bearings, (the ones that barely make any noise) You can…

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Steve Owner/Technician
Spokane, Washington
Steve Update
 

I have the thexton plug kit and used it on the master and no bleed off. Moved to the abs unit and no bleed off. Started connecting one line at a time and when I hooked up LR wheel it bled off as that caliper had a broken bleeder, installed new calipers at that point. Will try the line crimp as see if that does anything and also check for an aneurysm in one of the lines when full pressure is…

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Hollis Technician
Boulder, Colorado
Hollis Default
 

Is this the type of brake master cylinder the vehicle has? (see image) On Identifix this description in Tech Tips is all I can find of how it works. (Discalaimer: Tech Tip shared for professional use only. All credit given to Identifixes author. I'll delete if there are copy right issues ) [The unit between the master and the booster is called a brake pressure conversion unit. It will give…

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Hollis Technician
Boulder, Colorado
Hollis Default
 

Forgot, there's a bulletin for the Booster Check Valve for a noise complaint. Seems odd, but to me a noisy check valve would indicate ineffectual operation, might be worth a look. T-SB-0229-09

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Richard Mechanic
Brookhaven, Georgia
Richard Default
   

What does the pedal do with the engine off. Pump it engine off and check free play per SI. Then check reserve distance. Is it within spec or not? I don't know what the word dinamite is or what you mean. There is a cantilever that reacts from the pedal to the pushrod and on all of those one can force the pedal to the floor with brute force. They must be adjusted without vacuum assist to perform…

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Richard Mechanic
Brookhaven, Georgia
Richard Default
   

Very interesting website. I am curious why or for what reason I have a negative response for asking questions and suggesting SI procedures. For whoever decided to arrow down my reply, do you have the balls to state why?

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Richard Mechanic
Brookhaven, Georgia
Richard Default
 

I guess not.

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