Gs300 Bmcyl / Abs Booster Pump/ Accumulator C1223,c1252,c1256

[BillyM300]

Hi Guys n Gals,

1998/9 GS300 SE Auto Sport (Blue Mica)

I bought my little beauty just over 6 years ago, apart from the odd brake pads, bits etc, I've never had any problems at all and I can't fault its smoothness and such a quiet car. It was owned from new by the Chief Engineer at Lexus in Bracknell until I bought her.

Its really good and interesting to read all the info in this forum on varied technical issues with your invaluable but unfortunate experiences, especially with the dreaded "VSC, ABS, VSC Off & Engine Check" light etc, etc.

I have experienced this problem now for 3 months or so, first starting with the Eng check light on & the noise of somebody trying to strangle a chicken behind the dash. A couple of weeks or so later, the dreaded 3 orange lights came up accompanied by a high pitched annoying whistle (like a steam loco) and a distinctive click from the brake pedal, which came more frequently as weeks went past and now on permanently with never any change or loss in braking.

After doing my extensive trawl on hundreds of sites over this time retrieving ideas, tests, locating part outlets and info from this forum (thank you), I knew which way I wanted to go without being shafted for the whole unit or pump motor/accumulator......

Initially, I thought it best that Lexus carry out the necessary diagnostics coming up with C1223 (ABS Control System Malfunction), C1252 (Hydro Booster Pump Motor) & C1256 (Accumulator Low Pressure). After being told about the parts that needed to be replaced and the extortionate cost I would have to pay, I found a company down in Kent called BBA-Reman that specialises in testing (£150-£250) and remanufacturing (^£500) these units giving a warranty with it.

I was determined to find out exactly what was wrong with my unit, so I decided to have it tested. Lexus removed the unit and I sent it off to Kent giving them all info and fault codes. They said that they will test everything electronic, replace necessary parts and bench test but we don't test the hydraulics.

I received a call from them saying that we can't find any fault with it, the motor & accumulator, the ecu is working fine, the only component they couldn't test is the ABS Pressure Sensor (located at the front face of M/Cyl). It looks as if it has narrowed the fault down to this sensor. To eliminate this sensor, has anyone had experience with this and does anyone know how & where to test it?? Which brings me to another question.....why couldn't Lexus test this sensor whilst still on the vehicle, having brake fluid pressure already there and an individual check on readings being done on the terminal & connector?? Please correct me if I'm wrong but I think its just a case of a spring loaded diaphragm connected to a solenoid type action that gives out an open or closed circuit through 3 pins.

More to come after Lexus refit this unit.

If its any help to anyone, I'm more than happy to pass on any of my findings.

Regards

Billy M

[ColinBarber]

The ABS pressure sensor is used to determine the master cylinder pressure. There are two further pressure sensors that determine the pressure within the accumulator. There are ways to test them - measure resistances with with/without pressure, however there doesn't appear to be a way to test whether the pressure at which it switches is correct.

In all cases where the pressure sensors are suspect the repair manual states to replace the hydraulic brake booster assembly so it doesn't appear that these sensors are replaceable (at least by Lexus).

[BillyM300]

Thanks Colin for sending me your info and diagram, most interesting.

I'll get Lexus to test the resistances on re-installation and will let you know the outcome.

When and if I get this fitted and its still the same, would you happen to know how I can isolate firstly the high pitched whistle and the lights, or/and totally unplug the ABS, which I haven't got anyway?

Cheers

[probsat]

Thanks guys for all the input, managed to buy a 2nd hand unit fitted it bled it which was very difficult and all is now well again. I think I will buy a spare to keep in stock

 

cheers

 

probsat