Brake Gremlin

[werminghausen]

Sam,
I found myself yesterday looking around , searching for MB G280 or G300 (they are very simple, bullet proof...all mechanical, no electronics) ...which are mid 80s to early 90s.... but this is simply frustration and depression.
My T4R...I don't give up easily but the electronics frustrate me immensly.... what no mechanical problem typically does. I know I need to get this T4R going.

I had old MBs all my live (grew up in Stuttgart area) and was trained at Maybach factory back in the 70s... so yes I understand old MBs very well. I am not touching any thing younger than roughly beginning of the 90S.
New MBs are no different than other modern cars I guess.

 

[werminghausen]

I was pulling the plug on the pressure sensor from my current master cylinder (I hope I am correct that this is the triangular curved shape plug with 3 wires that connect to the pressure sensor. That sensor is connected/screwed directly onto the master cylinder.
Pulling that plug made no difference. I had the same alarm lights and sound.
Does that give you any hints? Is the pressure switch a potential failure?
I pulled all the other plugs as well, one by one....and no combination of active/inactive plugs changed anything regarding the alarms.

So in case I cannot make any substantial progress, my assumption is that I'll bite the bullet and order a new booster unit from Toyota for 1.4K...unless I find any mysterious ABS codes that lead to the wheel sensors as these are possibly the only outside parameters that could cause the drama..... what do you think?

Martin

 

[SocalSam]

In older Fords with Bosch ABS valve block and module, sometimes re-seating the module will cure problems. I don't know about AISIN but it is worth a shot before spending $1.4k. You still need an ABS capable scanner/reader to pull the codes to make sure wheel sensor is not causing issue. Are you able to limp the truck to Autozone or equivalent to have the codes read?

 

[werminghausen]

Thanks Sam,

I ordered the code reader that does ABS codes as well. As soon as it is here I'll try and read ABS codes.

I honestly doubt having a wheel sensor problem. This would be a big coincidence. But everything is possible- Murphy's Law

Brief Brake History recap
The brake alarms started 1/2 year ago during an incidenr when I got stranded because of a rusted out rear brake line (left rear) that caused a fluid leak and then I got the full alarm (pump ran out of fluid) and had no brakes. I had to tow the car back home 30 miles.
After preplacing the boken brake line I could not get rid of the alarm and I installed an ebay rebuilt brake pump and accumulator kit (that unit was not rebuilt but simply from a junk yard).... replaced the brake motor/accumulator and could drive again (no alarm after I stalled the rebuilt kit) but the brake motor came one every second brake action. During heavier braking I got the brake alarm for 15 seconds and that sacred the hell out of me.... that incident happened more frequently from then on.
Also the brake power was never good, pedal always soft, no matter how much I bled the brakes. The brake motor then started running at every single brake action until I changed the accumulator (old accumulator had onlt 43bar of charge). With a new accumulator (75 bar) I had the constant brake alarm and I am stuck since then.

I don't have an explanation for this behavior, my logic can't follow and I am scrambling since then.


Here is a good description of the 'hydroboost' system, also stating there is no manual from Toyote and no good way to diagnose the system. Toyota wants customers to replace the entire unit.

The unit uses an Accumulator Pump to build up hydraulic pressure which is stored in the Accumulator Tank to be used by the ABS Solenoid Pack & Master Cylinder for braking assist when you press the pedal. This provides far better assisting force than a traditional vacuum booster and allowed Toyota to use the ABS/VSC/TRAC systems to provide some benefits off road (i.e. TRAC functionality.) As a result of the design, the unit is combined into one large all-in-one unit and is very costly to replace when it does go bad. The master cylinder is bolted directly to the ABS Solenoid pack with high pressure brake fluid being fed into the passages, its all one big maze that is controlled by electronic solenoids and valves; where as on most vehicles the ABS Solenoid pack is separate from the master cylinder.
Unfortunately aside from DTCs (Diagnostic Trouble Codes) and/or process of elimination, there is no really effective way to diagnose these units in terms of pressure testing/electrical testing/ect. Toyota hasn't released any diagnostic criteria beyond what I mentioned in the above post and when my own personal 4Runner's brake master cylinder failed; I was unable to determine any other ways to diagnose the units.

I have read some infromation about replacing the stop lamp switch as this switch can interfere with the ABS pak.... Why that switch would interefere is a riddle to me.

Martin

 

[MikeinNH67]

Do you suspect- for instance- the speed sensors have an issue? Would they would trigger the same alarm that I am experiencing?
Martin

I don't think this is the case, I had a failing wheel speed sensor and all it did was set the ABS light and the other 2 TRAC type lights. No alarms. I used a Foxwell unit to pull the ABS code and monitor the sensors to find the failing one. This type bi-directional unit can help in some ways but you should be able to get away with a cheaper unit. Most ABS capable ones still are close to $100.

Curious, do you still have the old master assy? Did the one you bought come with the board AuSeeker mentioned?

 

[werminghausen]

Thanks Mike,
For the info that a bad wheel sensor would simply trigger the ABS and VSC lights (but not brake light and alarm sound).

The unit I bought on ebay was the naked Pump/Motor/Accumulator pack (No Black Box). That purchase was simply bad.
DONT buy 'rebuilt' brake parts for the T4R on ebay (as mentioned before the accumulator they sold as rebuilt had only 42 of the 75 bar charge and the pump motor appears to be simply from the junk yard as well).

I am waiting for the scanner and try my best to figure out any ABS codes.
However since the wheel sensors wound not trigger the brake light and alarm sound I can as well buy the new unit now.
Or do I have any other chance?
What do you think?

Martin

I just received the OBD2 & ABS tool, we'll see

 

[SocalSam]

Thanks Sam,

I ordered the code reader that does ABS codes as well. As soon as it is here I'll try and read ABS codes.

I honestly doubt having a wheel sensor problem. This would be a big coincidence. But everything is possible- Murphy's Law

Brief Brake History recap
The brake alarms started 1/2 year ago during an incidenr when I got stranded because of a rusted out rear brake line (left rear) that caused a fluid leak and then I got the full alarm (pump ran out of fluid) and had no brakes. I had to tow the car back home 30 miles.
After preplacing the boken brake line I could not get rid of the alarm and I installed an ebay rebuilt brake pump and accumulator kit (that unit was not rebuilt but simply from a junk yard).... replaced the brake motor/accumulator and could drive again (no alarm after I stalled the rebuilt kit) but the brake motor came one every second brake action. During heavier braking I got the brake alarm for 15 seconds and that sacred the hell out of me.... that incident happened more frequently from then on.
Also the brake power was never good, pedal always soft, no matter how much I bled the brakes. The brake motor then started running at every single brake action until I changed the accumulator (old accumulator had onlt 43bar of charge). With a new accumulator (75 bar) I had the constant brake alarm and I am stuck since then.

I don't have an explanation for this behavior, my logic can't follow and I am scrambling since then.


Here is a good description of the 'hydroboost' system, also stating there is no manual from Toyote and no good way to diagnose the system. Toyota wants customers to replace the entire unit.

The unit uses an Accumulator Pump to build up hydraulic pressure which is stored in the Accumulator Tank to be used by the ABS Solenoid Pack & Master Cylinder for braking assist when you press the pedal. This provides far better assisting force than a traditional vacuum booster and allowed Toyota to use the ABS/VSC/TRAC systems to provide some benefits off road (i.e. TRAC functionality.) As a result of the design, the unit is combined into one large all-in-one unit and is very costly to replace when it does go bad. The master cylinder is bolted directly to the ABS Solenoid pack with high pressure brake fluid being fed into the passages, its all one big maze that is controlled by electronic solenoids and valves; where as on most vehicles the ABS Solenoid pack is separate from the master cylinder.
Unfortunately aside from DTCs (Diagnostic Trouble Codes) and/or process of elimination, there is no really effective way to diagnose these units in terms of pressure testing/electrical testing/ect. Toyota hasn't released any diagnostic criteria beyond what I mentioned in the above post and when my own personal 4Runner's brake master cylinder failed; I was unable to determine any other ways to diagnose the units.

I have read some infromation about replacing the stop lamp switch as this switch can interfere with the ABS pak.... Why that switch would interefere is a riddle to me.

Martin

My attention span only goes back a few posts, lol. Did you rebuild master cylinder/abs block with new seals and cleared screen filters? I think I asked this a few pages ago but can't remember the answer. (It's an internet thing.)

 

[werminghausen]

Here are my current ABS codes 1-8 as they show on my new OTC 3208 scanner I just received (They claim this device is made in the US!)

1) C0278 open/short Circuit in Antilock Brake System Solenoid Relay Circuit
2) C0279 Battery Short Circuit in Anitlock Brake System Solenoid Relay Circuit
3) C1223 Malfunction in Antilock Brake System Control System
4) C1246 Malfunction in Master Cylinder Pressure Sensor
5) C1252 Hydro-Booster Pump Motor Malfunction
6) C1253 Hydro-Booster Pump Motor Relay Malfunction
7) C1254 Pressure Switch Circuit
8) C1256 Accumulator Low Pressure Malfunction


Wow... the entire spectrum of the Hydro- Booster Apparatus.
But no wheel sensor malfunction.

What do the experts say?

Martin

 

[werminghausen]

My attention span only goes back a few posts, lol. Did you rebuild master cylinder/abs block with new seals and cleared screen filters? I think I asked this a few pages ago but can't remember the answer. (It's an internet thing.)

Hi Sam,
no I did not disassemble the booster or master cylinder.
All I did was
1) exchanging the pump/motor/accumulator from original to the 'rebuilt unit'
2) exchanging the 'rebuilt accumulator' to a new accumulator.

Martin

PS I was inclined to take this unit apart but I never did

 

[SocalSam]

Codes. Looks like generalized control failure to me. Possible: module is bad, wiring issue, or fuse is blown. Check fuse 52 (40A) in engine compartment for 2003-05. I know you don't like ebay parts but if seller represents part as good, ebay will refund if part does not work. Look at this one:

2003 2004 2005 TOYOTA 4RUNNER ABS TRC VSC TRACTION SKID CONTROL 89540-35320 | eBay

 

[werminghausen]

Thanks for the information, Sam
Control failure: I am assuming the Skid Module is the control for the hydro booster's actuators for ABS, VSC, TRC ?? ( 5 Sockets, 2 in front and 3 directly into the black box, left side of hydro-booster)
It seems the Skid Module unit is located inside left side under the dash?
How difficult is it to swap this control unit?

Fuse 52 (40A).... I'll check

Martin

 

[werminghausen]

Hi Sam
Fuse #52 seems to be towing trailer lights?
Fuse #53 ABS Motor/Skid Module is a 40A, seems fine to me.
#55 is ABS solenoid /Skid Module 50 A, seems fine as well

Here is a good illustration for fuses of my 2003 T4R.

2003 Toyota 4Runner fuse box diagram - StartMyCar

 

[werminghausen]

My question is:

Is the problem in the hardware (hydro-booster) or is the problem in the Control Unit (Skid Module) ?
Or could it be both?
What do the ABS codes tell you?

Martin

 

[MikeinNH67]

You have some open/shorts that may contribute to other codes. I don't see how those would be a pump/master cylinder thing. Did you unplug connectors when you swapped the unit out? I'd be looking at all of those connectors first but kinda wonder if that control module has got issues, cracked solder joints or something. I'd hate to put $1400 into something and have it still not work. Does the new unit come with the electronics too?

Curious, do you still have the original pump/master assembly or did you have to send it back for a core charge?

It may be worth clearing the codes and see what you get at the first alarm sounding.

One last thought would be to clear the codes and jiggle wires and such to see if that sets off the alarm.

 

[werminghausen]

Thanks Mike,

I removed the hydro booster 2 times and during the process I was disconnecting the 5 Plugs from the hydro booster.
Since last booster removal I disconnected these plugs various times (nothing changed) and I cannot see any problem with the plugs.

I still have the original Pump/Motor/accumulator unit.

I am not sure if I understand what you mean with jiggle wires.

Triggering the alarm sound is simply putting the key into ignition.
Sometimes only the alarm lights come on but as soon as I hit the brake the alarms sound goes off.

The new unit is a direct replacement of the hydro booster- the entire unit.
The skid control module is not part of it.

If it is my best guess... I'd bite the bullet and order the new Hydro Booster plus a used Skid Module off ebay.
I don't know how to install the Skid Module. Is it simply removing the old one and plug the new one in?

Or is there some procedure?

Martin

 

[SocalSam]

C0278 and C0279 are electrical failures. The rest are sensor failures which could/should clear when the electrical issue is fixed. If the fuses are good, Mike makes a good suggestion regarding wiring. You may have chafed wires which are allowing unintended voltage or ground.

 

[AuSeeker]

You have some open/shorts that may contribute to other codes. I don't see how those would be a pump/master cylinder thing. Did you unplug connectors when you swapped the unit out? I'd be looking at all of those connectors first but kinda wonder if that control module has got issues, cracked solder joints or something. I'd hate to put $1400 into something and have it still not work. Does the new unit come with the electronics too?

Curious, do you still have the original pump/master assembly or did you have to send it back for a core charge?

It may be worth clearing the codes and see what you get at the first alarm sounding.

One last thought would be to clear the codes and jiggle wires and such to see if that sets off the alarm.

Mike you're misunderstanding what he said he replaced, he never replace the entire master cylinder assembly, he only replaced the "pump" that the electric motor runs and "accumulator".

 

[werminghausen]

Thanks Sam,
chafed wires:
I looked hard but I cannot find any problems with the wires and the plugs and sockets seem to be fine.
The only items I touched were the 5 plugs (which have to be removed whenever I took out the hydro booster).

I need to look under the dash and see if I damaged anything underneath while battling down below removing the 4 nuts at the hydro booster studs....
That would be a bummer, hey

Martin

 

[werminghausen]

C0278 and C0279 are electrical failures. The rest are sensor failures which could/should clear when the electrical issue is fixed. If the fuses are good, Mike makes a good suggestion regarding wiring. You may have chafed wires which are allowing unintended voltage or ground.

Both of the electrical codes C0278 and C0279 point to the ABS relay?
Could it be that this relay is gone bad?

Martin

I just see that there are 2 ABS Relays in the fuse box

1 ABS SOL Relay (solenoid)
2 ABS MTR Relay (don't know what MTR means)

How to test these creatures?

 

[AuSeeker]

Both of the electrical codes C0278 and C0279 point to the ABS relay?
Could it be that this relay is gone bad?

Martin

I just see that there are 2 ABS Relays in the fuse box

1 ABS SOL Relay (solenoid)
2 ABS MTR Relay (don't know what MTR means)

How to test these creatures?

The "MTR" could mean motor?