abs brake light buzzer going off C1356

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Thanks,
Bob Wilson

 

I am looking at replacing a bad brake booster pump/accumulator on my 2001 Prius with a used one from Ebay. I have the mini VCI to do the brake bleeding, but the service manual calls for disconnecting the AC lines and the brake lines. I don't have problems disconnecting the brake lines, but does anyone have any successes without disconnect the AC lines since it seems ridiculous for something that's supposed to be easy. How does the book time of half an hour calculated if AC lines have to be disconnected. I also noticed some screws on the booster pump body, can it be disassemble to avoid disconnecting the AC lines?

Thank you so much for any helps or recommendation

 

Thanks for the quick response. I was hoping that I don't have disconnect the AC lines, but it seems like that's outside of my skill level even though the rest looks easy. I already got the cowl and wipers out of the way and can see the booster pump within reach...

I see 4 screws at the bottom of the bracket that holds the pump in place. I will try to remove the pump without disconnecting the AC Lines. To me, it is easier to even bend the bracket rather than disconnecting the AC lines. Will update everyone whether I am successful or not. I put it at 50%.

 

Ok, after over 10 hours, I verified that you CAN take out the booster pump without disconnecting the AC lines. With an used booster pump I got on Ebay for $100, I was able to swapped out the old pump which was covered in brake fluid. With the right (passenger) wheel off, there's just enough room to squeeze the pump through with the bracket off. You might have to push some brake lines out of the way.

With the new pump installed, now I am a little bit confused about the bleeding procedure. The factory manual calls for bleeding of the booster. It says with ignition off, depress the brake 40+ times. doesn't mention anything about opening up the bleeder screw. Without the opening the bleeder screw, the brake is very hard to push. 40 times and no drop in reservoir. However, I can open the bleeder screw and the brake becomes much easier to push and the brake fluid comes out. I've refilled the reservoir twice that way, but the pump seems to run forever but still hard to push down on brake with ignition on. Am I doing something wrong here?

I will go get more brake fluid but someone that's done the brake bleeding share your experience. Should I continue to open the bleeder screw and depress the brake 40+ times until the pump stops after 30-40 seconds?

Thank you so much! I am hoping I can save about $2K this way. I can share more about how I changed out the booster, but really need some help with bleeding brake...

 

With the new Ebay Booster pump, I can clearly hear the pump running continuously when I turn on the ignition. I still get C1256 code, I think either I have a bad accumulator from the Ebay pump or my bleeding procedure is to be blamed. I really could use the help, I am so close. Someone must know how to bleed the system properly. If I wait with ignition on for over 5 mins, I get C1252, that's because the pump is running longer than it should. Which makes sense, something is causing the system not to pressurize.

Following the factory service manual, with ignition off, I pressed the brake 40+, nothing happened. did this many times, my neighbors probably think I am crazy. Had the wife pressed on the brake with bleeder opened 40+ times on both front brakes, fluid came out, refilled and still the same. What am I missing? Do we have any Toyota techs here?

 

Opps I was thinking inverter coolant:

Bob Wilson

 

The brake system can be more than a little confusing. I see that you are referring to the factory shop manual, which is good. There is another factory manual that you probably would do well to look at; it's called the New Car Features Manual and it is also available at techinfo.toyota.com. There is a NCFM for every time a new model is introduced, which means you want to look at the one for 2001. The regular shop manual gives the steps for working on the various systems, assuming you kind of know how the system is designed and intended to work. The NCFM is where you get that background info. The brake hydraulic system diagrams and explanations are pages 106 to 121.

I think Bob's comments about turbulence and pump running continuously must have been copy/pasted from a post about bleeding the cooling system.

Looking at the bleeding instructions in the FSM, you should remember they are generic instructions on bleeding the brakes for any reason. So, they start with 40+ strokes on the pedal (with ignition OFF), to use up any pressure in the brake accumulator. Naturally if you've just installed a new accumulator and the pump hasn't run yet, there won't be any pressure to use up.

Just like a conventional car with a vacuum booster, if you have just turned off the engine and there is still vacuum in the booster, you should be able to push the brake pedal a few times that feel easy (using up the stored boost), after which the pedal will feel hard. It's the same for the Prius except the boost comes from a pressurized accumulator tank instead of a big vacuum diaphragm. You don't need to open any bleeders for this part of the job; using up the boost pressure just means some fluid runs from the accumulator into the master cylinder and rear brakes when you press the pedal, and runs back up to the reservoir when you let the pedal up. 40 strokes should be more than enough to use up all the accumulator pressure that way. Probably long before 40 you'll be able to feel where the pedal suddenly feels extra hard. That's where your boost pressure has all been used up.

At that point, step 2(b) is to turn the ignition ON and let the pump run, to refill the accumulator, then go back to 2(a) where you turn the ignition OFF and empty the accumulator again by stroking the pedal (the fluid just ends up back in the reservoir). By repeating this accumulator-fill-and-empty dance until the fill step completes in 30 to 40 seconds, you should be pretty sure of having the air out of the pump and accumulator.

That's when you go on to the later steps of bleeding the various wheel circuits and the actuator.

In my (2001) edition of the shop manual, the wheel circuit bleed instructions are kind of self-conflicting and make me think maybe that part of the manual was written by three guys with different ideas of the best way to do it, and they didn't talk to each other. If you follow it literally, you end up bleeding both rear circuits twice, the left front twice, and never touching the right front. Oops! Maybe the editors caught that by your 2003 edition?

The nice thing about the actuator bleeding on the Gen 1 is that even though there are 11 different solenoid valves in that baby, you seem to be able to bleed it by activating only one, the SRrR. If you don't have the Techstream software to command it in that procedure, you should be able to refer to the Wiring Diagram Manual (also on techinfo.toyota.com) and find where you could work it with a jumper wire. I think that all got a lot more complicated for the Gen 2 and you're pretty much stuck needing Techstream to bleed one of those.

The manual strongly hints that energizing SRrR for more than two seconds at a time (with a 20 second cooling period between) could cause damage, so I'd be careful about that. As with bleeding the booster, the fluid releasing through SRrR just circulates back to the reservoir - you don't open any bleeder for that part.

-Chap

 

Thanks Bob and Chap! When I read Bob's discussion about the turbulence, I thought you were talking about the inverter coolant pump. I changed the inverter pump as a preventive maintenance, that by comparison was about 100 times easier.

I bought techinfo access for $15, but didn't find it very useful because I already have the FSM. I probably should have looked at the
NCFM, but no longer have access. Thanks for explanation on pumping the brake.

Going back to bleeding the pump and accumulator. I've now done it 5-6 times following step 2(b). Here's what I've observed. With code C1252 set, the pump will only run every 7 seconds for 2 seconds, I assume that's to prevent damages to the pump from running too long. I cleared all DTCs and the pump would run for about 15-20 seconds before the annoying buzzer kicked in. Should I continue with 2(b)? Again, there's no drop in fluid as far as I can tell.

If it is even significant, I also took a shortcut and haven't bled the rear brakes yet. I don't think the pump or the accumulator cares about whether the brakes calipers are bled, correct?

I will continue to do 2(b) for another 10 times and report back. I am now a little disappointed because I had high hopes for the pump to restore everything. Anyone know how much I can get rid of a 2001 with 143K miles? everything else works and it is still drivable with very bad braking performance and annoying buzzer.

 

Repeated bleeding procedure 2(a) and 2(b) about 10 times now. no change in braking efforts or pump ever developing pressure. I don't think it is supposed to be like that. I think I've exhausted everything I know to do, almost ready to give up. Should I sell it or take it to the stealership to get a second opinion?

 

Agreed, pumping fluid into the accumulator shouldn't be affected by what's downstream of the master cylinder. In fact, just the pump and accumulator part of the system doesn't seem complicated enough for there to be very many possibilities for what's going on here.

If the pump runs and runs and runs, one of two things is happening. Either the pressure really is building up but the pressure switch is faulty and not turning the pump off, or no pressure is building up. You're saying the the pedal effort stays hard all the time, so it sounds like no pressure is building up. (Also, if pressure builds up, you can kind of hear the change in pump sound as the pressure builds and it works harder.)

If no pressure is building up, one of two things is happening. Either no fluid is getting pumped into the accumulator (is the suction hose from the reservoir to the pump intake plugged or kinked somehow? is the suction hose connected to the right nipple on the reservoir and the right one on the pump?), or fluid is getting pumped into the accumulator and not staying there.

If fluid is not staying there, it's either leaving the system or going back to the reservoir. If it were leaving the system, you'd see the reservoir level getting lower and the puddle on the ground getting bigger. So it's going back to the reservoir. The path could be through the relief valve built into the booster assembly (not seating correctly? maybe a piece of grot caught in it?), or the spool valve in the master cylinder isn't blocking off the flow completely. (There's a path back to the reservoir from the actuator too, but fluid shouldn't be getting to the actuator unless, again, the spool valve isn't stopping it.)

If you find the hose from the forward end of the master cylinder back to the reservoir and disconnect it, and run the pump, does fluid come out of the master cylinder nipple it was connected to? That'd indicate the spool valve.

Or if there's a disconnectable hose from the relief valve back to the reservoir (I can't quite tell from the diagrams), is that where the fluid is returning from?

If it costs you another $15 to renew your techinfo access and download the NCFM diagrams, that's less than what you'll spend at the dealer, or what you'll lose on the car if you give up and sell it broken....

-Chap

 

Have to take a business trip, so I will bleed the rear brakes next week. Thanks for your inputs Chap! I will think about how to approach it. It might be just time to sell the car. How much should I ask for? Is it worth $1500?

 

I don't have much of a sense of how to price the car (where are you located? I've seen signs of very good value retention in the US northwest....) - but, even before bothering with bleeding the rears, if it were mine, I would do some quick experiments to see why the accumulator pressure isn't building. Will you have a chance to pull the return hose off the nipple at the forward end of the master cylinder, activate the pump, and see if any fluid is escaping from that nipple (with no pushing of the brake pedal)? That would test one of the only two likely paths I am seeing for where your fluid could be going.

The other one would be the return-to-reservoir path from the accumulator relief valve, but I don't have any diagram that clearly shows me how that's routed, so it's probably easier for you to find (with your cowl presumably off, and having just recently performed the installation). Do you still have the old pump?

-Chap

 

Hey rlin78,

Not sure how long your business trip was, so I wondered whether you had had any chance to check for where the fluid is returning from ... seems like a more pressing question at the moment than bleeding the rears.

-Chap

 

Chap,

Just got back from my trip, have not had a chance to check the fluid return to the reservoir. My thought is that the hose from the reservoir is the only source for the brake fluid during the bleeding, so if I can bleed the brake, that means the hose is not blocked. I have not disconnected any of the other brake lines yet.

Someone else with a similar issue said that it could be the master cylinder. But the FSM also says that master cylinder is the issue if you are having spongy or low pedal, which is not my case. I did drive the car before I left to charge up the hybrid battery, the car still drove fine and stopped fine with extra efforts. That told me that I probably put everything back correctly, now the difficult part is figuring out why I am not getting any boost from the booster pump.

- Linn

 

Hi Linn,

If you look on any of the hydraulics diagrams (New Car Features Manual), they'll show not one but three hoses at the reservoir. One supplies fluid from the reservoir to the pump, for charging the booster. One runs directly from the reservoir to a nipple on the master cylinder toward the rear; this is a supply for the direct hydraulic circuit that works the front brakes when all else fails. The third connection at the reservoir goes to what looks in the diagram like a four-way union, and it is the return hose carrying fluid back to the reservoir. The other three ports on the union are the three places the fluid can come back from: one is a nipple on the master cylinder near the front end, one is on the brake actuator (the big square box on the firewall with umpteen brake lines), and one is the relief valve from the booster pump.

Now, the diagrams are drawn in the way that makes the most sense, not always the perfect representation of how stuff is built. I haven't had my reservoir off in a year or so, so I don't remember whether there really are three hoses connected to it. Maybe there's just one hose, or two hoses, and a union somewhere below it that splits off the three diagrammed circuits. I'm counting on you for this part because you've looked at it more recently than I have. Also, I don't know whether the four-way union that the diagram shows in the return line is a real four-way sitting in the open with four hoses on it, or maybe something machined into the aluminum block that the pump and accumulator sit on, with other lines attached to it. It might take a bit of squinting at the real physical construction to figure out how it conforms to the diagram.

But anyway, your ability to bleed the (front) brakes depends on the fluid path from the reservoir to that nipple at the rear of the master cylinder. It doesn't necessarily retire the question of a blocked path from the reservoir to the boost pump.

After all, if you hear the pump running, and pressure isn't building, there are only two things that can be happening: fluid isn't getting pumped into the accumulator (not reaching the pump for some reason), or it is getting pumped in and flowing right back out, returning to the reservoir.

If it's the second, it can only be returning from one of those three places connected to that return union: the nipple at the front of the M/C, the return port on the actuator, or the relief valve on the booster/pump. Find one of those three with fluid coming out when the pump runs (and nobody's touching the brake pedal), and you know where your trouble is.

-Chap

 

Chap,

I have some wonderful news to share. After your message, I remembered that I had a hard time with the hose that's going from the bottom of the reservoir to the booster because I forgot to tuck it through before tying down the booster pump. as a result, I had to pull very hard on the hose to get it to connect back to the reservoir. As you can see, I only followed the FSM where I thought made sense and took a few shortcuts. I also didn't disconnect the two other hoses on the sides of the reservoir. One can flip the reservoir over and push it with the two hoses still connected out of the way.

Anyway, the short story is that I loosen the booster pump, noticed that the hose was completely pinched in the corner and wasn't able to deliver any fluid to the pump. Once I straighten up the hose, everything was good. The FSM bleeding procedure started to make sense. Still, following the FSM bleeding procedure took another 2 hours to complete because it was tedious. I also had to wait for the wife to push the brake pedal.

You inspired me to take another look at the pump, and you reminded me there were two additional hoses that were delivering brake fluid from the reservoir to the calipers. Because of the shortcuts I took, I never remembered them until you mentioned it. Today is the first day driving 10 miles to work with my car after being out of commission for almost 3 weeks. No problems so far, knocking on woods. I also learned a lot about how the brake system works. It is complicated, but I also appreciate the engineering efforts that's done on it to make it safe in my opinion. I hope I didn't do any damages to the pump by running it dry without brake fluid for probably 1-2 hours while troubleshooting.

I put the total time to install a new pump with my method at about 15-20 hours if you are like me without a shop or power tools, longer if you have not done it before or know what you are doing (probably not a good idea). with a power lift and tools, you can probably cut the time in half and you don't have to disconnect the AC lines or the brake line in the wheel well if you are brave like me because you are pushing it down instead. The booster pump is a lot heavier than it looks BTW. I did use the mini VCI with techstream software from you know where to do the brake bleeding. Even without the brake bleeding, the car drove fine and didn't feel like there's any air trapped. But I didn't want to take any chances on that. So I did a complete flush of the entire brake system by following the bleeding procedure. Now my brake fluid looks fresh. I recommend buying the gallon DOT 3 fluid from Walley world for about $15. It is cheap and yes, you will need a lot of brake fluid if you are bleeding. You don't want to run out in the middle of bleeding.

Thanks again Chap! I am one happy man. Now if I can only get the wife to drive the car again...

- Linn