C1202 = A7/7s1 (BAS Release Switch) : Plausibility

SDS diagnostic steps say to check the pressure switch (B34) and it's wiring. Pressure should be 179psi (not sure if your tester can read that) , and check the voltage using the socket box connector, pins 18 and 19 should read 4.75-5.25v

It also suggests checking the release switch itself, its on/off reading should match the brake pedal usage. Pins 28 and 27 should read less than 1v with the brake pedal depressed, and normal vehicle voltage with it not depressed.

 

Hi

Sorry for questions but i am green with this subject.

Pressure switch b34 - what is it and where is it located?

I am not sure if tester can read it. It has lots of options etc etc

I could check voltages but where? Is it something what i could check myself?

Thanks

 

Here is a photo showing the location of the pressure sensor:

http://benzbits.com/w203/ESPPressureSensor1.pdf

Check the wiring harness to make sure it's not damaged or unplugged. The test that SDS indicates requires a special ECU connector wiring harness so that you can check the voltages on it's connector. You could just replace the pressure switch and see if that fixes the problem (not sure of the cost).

 

Thank you
I will check this out.

However there is no errors on dash or any problems with driving or braking.
This code has hidden in ecu.

So what does this sensor do? Is in linked with brake booster or servo?
Thanks

 

Hi
Just forgot to ask

What is full name for sensor? Brake pressure sensor or? Just trying to work out how to find it in shop

When u said to check pressure (179psi) did u mean this sensor holds vaccum (air) or brake fluid?
Thanks

 

Officially, it's the "brake pressure sensor". The pressure check if for the brake fluid pressure, and that is something that is checked via SDS - not physically with a gauge.

 

Thank You!

I didn't check it in my car yet as we have lovely weather in the UK(rain rain rain) however looking at your attachment looks like i will need to drop some brake fluid to replace the sensor. I belive that i'll need to bleed the brake system after replacement or no?

Thanks

 

Yes, if you are going to remove the brake pressure sensor, you will need to suction the fluid from the reservoir beforehand, then refill and bleed the brakes afterward. If you haven't changed brake fluid in the past two years, this might be a good time to do that. I like to use ATE racing fluid. They sell it in "Super Blue" and gold. Alternate between the two so you can use the color change as an indicator that you have fully flushed the old fluid.

 

Thanks Rudeney
Very helpful