Diagnosing Hydraulic Brake Booster Problem

[Simon12]

Hi All,

I've also posted a note in the new members section but not sure if it's the right thing to do to buy the virtual drinks in before dealing with a problem :winky:

As per the title, I've experience the dreaded brake warning lights - abs, vsc and warning buzzer and sudden loss of braking power on my 99 GS300 sport (112k miles now). On first assumption I thought it was going to be the full hydraulic unit, which of course it might be, but I thought it's best to check first.

I managed to ferret out a test procedure for power to the unit and I've checked continuity between pins on the two power sockets which show continuity correctly. Unfortunately, I haven't been able to find the relevant pages for testing continuity of cables or solenoids and their resistance (and thus abs ecu) without the use of the toyota special diagnostic tool.

I was therefore wondering whether anyone here has this information for testing with a good old multimeter and can help me?

Additionally, I've noticed slight wetness around the hydraulic unit so suspect there may be some fluid leakage and I also wanted to test the pump function but I'm unsure of how best to go about this.

I've been considering whether to get an OBDII tester now so that at least I can go through and check what I can before stumping up the cash for the entire booster unit as I know how much this costs (if the tester is of any use here?)

Any assistance would be very gratefully received.

Many thanks,

Simon

[Simon12]

I must admit I'm a bit disappointed nobody's bothered to reply!

Anyway, I ended up sending the unit to a company called BBA-Reman, a remanufacturer, who have come back to say they can't do anything with the unit - it was worth a try. So, while I still haven't been able to do a full test myself, I've plumped for a new unit. Surprisingly I've got a good price through Lexus at just over 1500 quid all in.

Now, anyone who has changed out this unit before, can you confirm whether the ecu needs anything reset and advise a suitable OBDII scanner that can read the abs system ecu as most cheapies don't seem to be able to do this? Will the pc based scantool and related software do this or is there another make/model?

I would really appreciate some help here.

Cheers,

Simon

[dave1]

I must admit I'm a bit disappointed nobody's bothered to reply!

Cheers,

Simon

I didn't reply because it was not something with which I could have been of any assistance. I would think that other members were in a similar situation as normally the help and advice on this forum is really good. Hopefully there will be someone who can give you some information which will help you at this point.

[garethr]

I don't know anyone who has changed the brake booster on a GS, but I do know people who have changed the very similar unit on the Soarer, and they didn't mention an ECU reset.

As far as the ABS codes are concerned, my local garage has an OBDII reader which works for the ABS codes on my GS, although it cannot read the main ECU codes.

[Simon12]

Thanks for the input guys, I appreciate it.

As soon as I get the unit I'll update on my experience of fitting it.

I wonder whether the local garage having a reader that reads abs codes but not main ecu codes points to a requirement for different readers.

All the best,

Simon

[norlec]

I must admit I'm a bit disappointed nobody's bothered to reply!

Anyway, I ended up sending the unit to a company called BBA-Reman, a remanufacturer, who have come back to say they can't do anything with the unit - it was worth a try. So, while I still haven't been able to do a full test myself, I've plumped for a new unit. Surprisingly I've got a good price through Lexus at just over 1500 quid all in.

Now, anyone who has changed out this unit before, can you confirm whether the ecu needs anything reset and advise a suitable OBDII scanner that can read the abs system ecu as most cheapies don't seem to be able to do this? Will the pc based scantool and related software do this or is there another make/model?

I would really appreciate some help here.

Cheers,

Simon

Hi Simon

I also had your problem with my 1999 GS300 Sport and you will find from other members on the forum although Lexus have put the connector in for an OBD11 scanner there is not a scanner on the market thats works as they weren't set up for it I tried 3 and none worked.

Garages with the proper scanners will be able to read the codes but when I enquired from various companys the cheapest for these cars was £1650.00 which is a proper garage scanner,I also had to replace my brake master/booster unit because as you found out they cannot be repaired I got mine from eBay brand new still in the Lexus box for £900.00 which was very lucky.

I had my unit fitted by an indie garage that I used to service my car and they had one hell of a job and had to contact Lexus in the end so if you are thinking of fitting it yourself be aware it is a B-----d of a job.

Good luck

Norman

[TheGuv]

I'm in a similar situation to simon12 as my 2001 GS430's brake booster assy failed with the usual lights, buzzer etc. I was gutted as I read before I bought the car 6 months ago that the series 2 have an uprated unit which fixed the original problems. Wrong.

My local Toyota/Lexus independent have tried replacing the pressure switch(es), the pump, the reservoir and finally sent it to BBA-Reman who replaced stuff for under 300 quid, which was great although could only test 95% of it on the bench. Unfortunately the problem remains (they've refunded in full)

I've had zero luck on eBay or breakers, so I suppose I'll have to get the complete unit from lexus at a cost of about 2100 +VAT. <gulp>

Can anyone confirm the following? :

47210L is the Brake Booster Assy, W/Master Cylinder; which comprises

47201 Cylinder Sub-Assy Brake Master; and

47070B Pump Assy w/Accumulator

I think from info on the 'net that part 47025-300230 Cylinder Sub-Assy Brake Master which isn't shown on my exploded view is the actual part I need (the master cylinder) which is 600 quid cheaper as it doesn't have the reservoir or pressure switch -- Can anybody confirm/

'guv

[Simon12]

I'm in a similar situation to simon12 as my 2001 GS430's brake booster assy failed with the usual lights, buzzer etc. I was gutted as I read before I bought the car 6 months ago that the series 2 have an uprated unit which fixed the original problems. Wrong.

My local Toyota/Lexus independent have tried replacing the pressure switch(es), the pump, the reservoir and finally sent it to BBA-Reman who replaced stuff for under 300 quid, which was great although could only test 95% of it on the bench. Unfortunately the problem remains (they've refunded in full)

I've had zero luck on eBay or breakers, so I suppose I'll have to get the complete unit from lexus at a cost of about 2100 +VAT. <gulp>

Can anyone confirm the following? :

47210L is the Brake Booster Assy, W/Master Cylinder; which comprises

47201 Cylinder Sub-Assy Brake Master; and

47070B Pump Assy w/Accumulator

I think from info on the 'net that part 47025-300230 Cylinder Sub-Assy Brake Master which isn't shown on my exploded view is the actual part I need (the master cylinder) which is 600 quid cheaper as it doesn't have the reservoir or pressure switch -- Can anybody confirm/

'guv

Hey 'guv,

I'm sorry, I haven't been on here for a while. I can't confirm the part numbers bit it seems that once these things go, it's best and eventually most economical to replace the entire unit.

I got my raplacement unit for £1521 incl. VAT and shipping from Lexus Parts Direct who are an authorised Lexus dealer, so it is genuine. Hope it's not too late and you've already been stung for the 2k plus price.

Hope this helps,

Simon

[Simon12]

[

Hi Simon

I also had your problem with my 1999 GS300 Sport and you will find from other members on the forum although Lexus have put the connector in for an OBD11 scanner there is not a scanner on the market thats works as they weren't set up for it I tried 3 and none worked.

Garages with the proper scanners will be able to read the codes but when I enquired from various companys the cheapest for these cars was £1650.00 which is a proper garage scanner,I also had to replace my brake master/booster unit because as you found out they cannot be repaired I got mine from eBay brand new still in the Lexus box for £900.00 which was very lucky.

I had my unit fitted by an indie garage that I used to service my car and they had one hell of a job and had to contact Lexus in the end so if you are thinking of fitting it yourself be aware it is a B-----d of a job.

Good luck

Norman

Cheers Norman,

I saw your reply to my post about a compatible odb2 scanner http://www.lexusownersclub.co.uk/forum/index.php?showtopic=62893 which works a treat but I have had problems accessing the transmission data. All other data such as engine, abs and srs are good.

The fitting of the unit was fiddly but, in my experience fairly straight forward mechanically. Here's a brief description of the process:

1. Get syringe and remove brake fluid from the reservoir.

2. Put some old rags/cloth whatever underneath and around the boost assembly.

3. Disconnect the ecu and power connectors from the unit and unscrew the throttle cable bracket.

4. Loosen the nuts for the brake lines - 2 at the front of the unit, 2 and the side (don't touch the red coloured one underneath as that's from the accumulator) - and pull those line out of the unit.

5. Get inside the car under the steering wheel and remove the parts of the fascia obscuring access to the brake pedal (iirc 3 part of fascia come off and you'll need to disconnect the petrol/boot switch unit).

6. Remove the brake pedal spring and r-clip etc. that connects the master cylinder with brake pedal and then unscrew the 4 nuts holding the booster unit in place on the chassis - the one on the top left side is very difficult to get to.

7. Lift/pull out the old unit - gently and carefully so as not to get brake fluid all over the place.

8. Put the new unit back in. in reverse order - the 4 nuts holding the master cylinder assembly to the chassis are tightened to 18nm iirc (but do check as my memory may be incorrect).

9. Fill the new unit with brake fluid and then with ignition still of pump the brake pedal more than 40 times.

10. Reset the abs ecu - this is a must as the unit doesn't work correctly if there are critical error codes still stored.

11. Bleed the brake system - this is where it is different from the procedures I've seen written about this but here goes as it is the proper method according to the lexus manual:

- with ignition off pump pedal rapidly more than 40 times - the pedal should get heavier to pump during the process

- turn the ignition on and listen to the accumulator pump which should turn off within 30-40 seconds.

- now pump rapidly the brake pedal 20 or more times (warning buzzer will go off and should then go off after a little while)

- with the ignition remaining ON bleed the the brake system but start with the front right (i.e. drivers side), then front left side. Going on to the rear, start with left side and then right side.

(as a note while bleeding the system it isn't necessary to pump the pedal several times before opening the bleed valve because the pump and accumulator maintain system pressure. this also can't be done if you're bleeding the system on your own). You will hear the pump switching on and off during this procedure which is entirely correct.

- make sure you have a lot of brake fluid I used nearly three liters in total due to some stubborn air pockets, so be patient and always put the lid back on the master cylinder reservoir.

- if you're doing the bleeding on your own an ideal tool is the europat vizibleed - it's about a fiver from Halfords. no need for expensive pressurised kits.

- with this kit you can press the pedal a few times then walk round the car to see if there are bubbles in the tube, top up the reservoir and then return for more pedal pumping - just don't open the bleed nipples too far as fliud may seep out there instead of the tube.

- finally, once bled, turn the ignition off and again pump the brake pedal more than 40 times and check fluid level, topping up as necessary. You're done.

Hope this helps,

Simon