Brake Booster pumps continuously and overheats (1 Viewer)

[Leo KE]

HDJ100 1HD-FTE VX ex-UK

Sorry for the long thread but I'm pulling hair out and would hate to go bald over this. Here's the problem and also some background on my car and what we have done so far. Any and all ideas very welcome ! Thanks

Current problem:
- The Brake Booster motor (47070-60010) is overheating, due to the brake booster motor coming on (pumping) too often.
- The motor comes on even without the driver having pressed on the brakes.
- There are no errors appearing in vehicle diagnostics (Techstream).
- After some time, due to the Brake Booster motor overheating, the brakes will fail.
- There are No visible leaks on any brake lines! No ABS buzzer or ABS or parking warning lights.

Tools / Spare Parts used:
- All spare parts are genuine Toyota parts, purchased from one of the dealers of Al-Futtaim motors in Dubai, UAE
- Techstream has been used for Air bleeding and diagnosing errors.

How to reproduce the problem:
- Bleed the brake system with manual bleeding and air bleeding (front only)
- The vehicle behaves normally and brakes feel OK.
- Drive the vehicle for several hours in some traffic and also long distance (total driving time is approximately 3 hours)
- Brake booster still appears to behave normally. According to my observation, this "normal" behaviour means that the motor will come on either when:
- a) vehicle is stationary and brake is pressed 2 times
- b) vehicle is moving and brake is pressed 4-6 times
- Leave the car parked overnight.
- Drive the car again in some traffic the next day.
- Stop the car, check the brake booster. The motor is now coming on even without the driver having pressed the brake pedal. And the motor (and accumulator) are getting very, very hot.

How to get rid of the problem (temporarily):
- Bleed the brake system with manual bleeding and air bleeding (front only)
- Brake booster behaves normally until you repeat the above steps to reproduce it (ie. drive the car for some time).

Background on the repairs which we have done so far:
- Brake warning lights ABS and Parking Brake and BUZZER came on and brakes lost functionality in July, 2015.
- Replaced Brake Master cylinder (47025-60022, only the master cylinder, not the complete unit) in October 2015.
- Brakes worked for a few weeks then ABS warning light coming on again
- Replaced Brake Booster w/Accumulator (47070-60010) in November, 2015.
- Brakes worked for a few days and problem started again. This was the first time when I paid attention and noticed that the Brake Booster Motor was getting very HOT. The Accumulator Assy is also getting hot, I assume due to heat conduction from the motor.
- After this, we have tried various replacement parts:-
- New complete front calipers (47730-60090, 47750-60090)
- Replaced all All 5 Flexible Hoses (90947-02A09, 90947-02A13, 90947-02A10, 90947-02A21, 90947-02A27)
- Replaced ABS ECU (89540-60070)
- Replaced Rear Brake Cylinder KIT (04479-60060)
- Even replaced the engine-side steel brake lines and joints, since we were fearing that air was getting in somewhere.

Other tests done:
- Car was parked, started engine from cold start and engine left running on idle.
- Immediately after switching ON, the Brake Booster pump was coming on (was pumping) for 7 seconds; and going off (stopped pumping) for 15 seconds
- After 1 hour of idling, the Brake Booster pump was coming on (was pumping) for 13 seconds; and going off (stopped pumping) for 8 seconds
- Car was switched off and parked for the night.
- The next morning, the Brake Booster pump is pumping for 11 seconds and going off for 7 seconds.
- Start the engine and drive the car, applying emergency brakes so as to trigger the ABS.
- Observe Brake Booster goes on LESS FREQUENTLY, going off for 45 seconds.

 

[PADDO]

With the constant short cycling I'd expect to find a low charged accumulator (but you've replaced that); failed H or L pressure sensors; a relief that's prematurely dumping pressure or some other internal leakage problem. The sensors have DTC associated with them which you'd expect to see if that's the root of your problem but you can't rely 100% on them being thrown. I'd check your BA pressure sensors as it seems most everything else has been replaced.

 

[Leo KE]

With the constant short cycling I'd expect to find a low charged accumulator (but you've replaced that); failed H or L pressure sensors; a relief that's prematurely dumping pressure or some other internal leakage problem. The sensors have DTC associated with them which you'd expect to see if that's the root of your problem but you can't rely 100% on them being thrown. I'd check your BA pressure sensors as it seems most everything else has been replaced.

Thanks PADDO where would one find the BA pressure sensors and how to check them ?

 

[PADDO]

I'm having trouble uploading diagnostic instructions but if you google DTC C1254, C 1256 you should get relevant hits in the LC manual part RM 731E. These will give you the pin outs and expected values. The pressure switch is on the side of the accumulator assembly. Your problem obviously may not be related to the system's pressure sensors but from what you've described the system is short cycling as the pump is suppose to run for 30 to 40 seconds then shut off until the next charge cycle is required. It's not designed for constant cycling, that's why it's getting really hot. The fluid level within the reservoir should drop about 11mm from its highest level (accumulator discharged) when the accumulator is charges. Generally, in any hydraulic system if you have short cycling you look for a failing control component (pressure switches); internal leakage; low accumulator charge or a relief that's not closed properly.

 

[ihadmail]

Could this be as simple as a bad relay? If the relay is starting to go it could cause actuation of the booster pump without an actuation signal.

 

[Leo KE]

Could this be as simple as a bad relay? If the relay is starting to go it could cause actuation of the booster pump without an actuation signal.

Worth considering, but would it somehow jive with the return to normal functionality after bleeding?

 

[ihadmail]

After bleeding, not necessarily. But for a relatively inexpensive easy to change piece I would personally give it a shot.

 

[bctlex]

After bleeding, not necessarily. But for a relatively inexpensive easy to change piece I would personally give it a shot.

Many years ago, one of my neighbor own a Corolla which was doing something weird - I dont even remember what the problem exactly. So myself and another neighbor tried to help figure this out - we spent hours until around midnight on the driveway trying to figure this out. We ended up replacing a relay from another car as a shot in the dark (literally), and that was the cause of the problem.

I have been told to replace the easy and cheap component first to rule them out before moving into the more expensive components.

 

[Skidoo]

If the relay contact is sticking, could be an off and on thing. The pressure sensor ( don't know where they are) could be the issue. Next up the list would be the control unit, but don't know which one controls motor, could be brake, VSC, or ATRAC.

 

[Leo KE]

I'm having trouble uploading diagnostic instructions but if you google DTC C1254, C 1256 you should get relevant hits in the LC manual part RM 731E. These will give you the pin outs and expected values. The pressure switch is on the side of the accumulator assembly. Your problem obviously may not be related to the system's pressure sensors but from what you've described the system is short cycling as the pump is suppose to run for 30 to 40 seconds then shut off until the next charge cycle is required. It's not designed for constant cycling, that's why it's getting really hot. The fluid level within the reservoir should drop about 11mm from its highest level (accumulator discharged) when the accumulator is charges. Generally, in any hydraulic system if you have short cycling you look for a failing control component (pressure switches); internal leakage; low accumulator charge or a relief that's not closed properly.

Took the vehicle into Toyota Kenya and here's what they say. Note that we had switched out the ABS Actuator assembly (Black /silver box on the side of the Master Cylinder), so what is being tested is actually the old ABS Actuator with new Cylinder and Booster... We did this as someone had suggested putting in the old unit to try. It gave similar visible results as the complete new Master unit (cylinder and ABS actuator):-

From Toyota...
So far we Carried out Physical inspection and Bleeding as necessary based on repair manual guidelines as below:-
>>No physical damages and Brake fluid leakages has been noted.
>>No Air lock noted.

>>We did ABS electrical circuit inspection as per repair manual and all was found to be ok.

>>ABS ECU inspection was also done both physically and electronically check and found to be ok.

>>We finally inspected the ABS Actuator Assy.

>>Based on the retrieved DTC and data list analysis, we do suspect the ABS actuator inbuilt solenoids are not functioning at times
Hence leading to internal fluid pressure leakage inside the Actuator assy.

The more detailed report says:-
A Diagnostic trouble code was finally retrived-(C1256)-ABS Accumulator low pressure), after having done check mode. The retrived DTC could not be cleared off and also indicated as a currennt (X) malfunction.
ABS Actuator Assy as seen in the Electronic Parts Cataloque.<<Please note that this actuator unit assy should be replaced as a complete unit>> reference to the below part number. <<47050-60022>>
1. Based on the retrived DTC and Data list analysis it was noted that during the brake pedal operation the ABS solenoids (inbuilt in the actuator assy) could not change from OFF to ON, They remained OFF position through out the Brake operation.Reference to above data list.
2. Currently the brake system is operating under fail save mode, meaning that it is operating like the ordinary Hydraulic/mechanical brake system.
The ABS actuator assy needs replacement with a new one and Genuine <<reference to the Part number above>>

Note: There was (and always has been as far back as I can remember), a line on the Data List in Techstream reading ECU/IG Power Voltage: TOO LOW.

Basically I'm being told after talking to the technician that having replaced the Master (47025-60022) and Booster/Accumulator (47070-60010) separately will NOT work and have to buy a complete new master (47050-60022)... again. Needless to say my pockets are empty and this sounds ridiculous.

-> Is there any technical reason why replacing the Master and Booster/Accumulator parts separately would not work ?
-> How sensitive are the Solenoids in the ABS Actuator - could the new one have broken already ? Assuming the behaviour with the new one and old one which is currently in the vehicle are indeed the same root cause.
-> Is there some calibration needed for the solenoids that can't be done with Techstream ? Why would the ABS solenoids sometimes not respond ?
-> What is Check Mode and why does C1256 only come up then ?
-> Does removing the ABS Actuator from the Master assembly ruin it ?
-> Does "ECU/IG Power Voltage: TOO LOW. " have anything to do with this ?

Many thanks again!

 

[grundsethp]

This is a good reference document. I had issues also and my pump was always running. The high pressure sensor on my abs module was sticky in coldish temperatures and a couple days of no use. I saw another post in the 4runner forum and he would depressurize the abs system after stopping. I seems to work. Good luck.

http://www.ezdries.net/Vidpics/ATRAC/LC100 new features.pdf

 

[Leo KE]

This is a good reference document. I had issues also and my pump was always running. The high pressure sensor on my abs module was sticky in coldish temperatures and a couple days of no use. I saw another post in the 4runner forum and he would depressurize the abs system after stopping. I seems to work. Good luck.

http://www.ezdries.net/Vidpics/ATRAC/LC100 new features.pdf

Should I assume u mean the high pressure solenoid and not sensor? Do you have a reference of how the abs actuator is built internally? Thanks!

 

[grundsethp]

Actually there are two pressure switches that control the pump.
This is what I did before to diagnose my issue:
Abs issue some work done but stuck?

If you want the 1000 page diagnostic manual, message me your email address.

 

[grundsethp]

I looked thru the diagnostic manual and c1256 is a low pressure switch issue. I would make sure the connector pins on the brake booster are straight and not dirty. Try to clean them with electrical contact cleaner. I would also rebleed the rear via techstream and front brakes.

The toyota dealer should be able to do a complete bleed. I think you may have air or dirty fluid still in your brake module.

 

[CruisingAndy]

hi i am Andy from germany (bavaria)
i have same message by techstream on my LC 100 Diesel
maybe somebody know how we can solve this problem

 

[CruisingAndy]

View attachment 2013687

 

[l3n0x]

hi i am Andy from germany (bavaria)
i have same message by techstream on my LC 100 Diesel
maybe somebody know how we can solve this problemView attachment 2013688

I also have this in techstream. My booster pumps a lot. Don’t know if its related and will fail soon or not

 

[l3n0x]

hi i am Andy from germany (bavaria)
i have same message by techstream on my LC 100 Diesel
maybe somebody know how we can solve this problemView attachment 2013688

By the way. Do you have the toyota alternator? I have an aftermarket one and that’s my main suspect. I’ve read about a guy who had a broken wire comming from the alternator (some kind of sensing wire), who had this issue and after fixing that cable all was fine.

I have not yet investigated this on my car, but I have a feeling that either that wire is broken or my aftermarket alternator doesn’t put out, or not that way that sensing signal that the toyota one does.

 

[CruisingAndy]

Thanks for reply
I will check the alternator,but i think it shows a problem with ABS or brakebooster

 

[l3n0x]

Thanks for reply
I will check the alternator,but i think it shows a problem with ABS or brakebooster

I know it sounds strange, but:

Hi From The Netherlands & AHC Issues

how did you manage to remove the ECU? I'm having a hard time...it's pretty tight quarters up there! does unbolting the ecu brackets and leaving the connectors attached give you enough room to test on the back of the connectors? I can't figure out the upper most of the two ecu mounting...

forum.ih8mud.com