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Pressure sensor shown as No2 in diagram above. Only one sensor is shown, the other is directly in front of the one shown

OK, so your BMW E46 has the DSC and Handbrake light on, You have got the car scanned and it shows 5E24 or 5E21 “Pressure sensors”. This is from a job we had today. Using the GD860 we scanned the car and had these codes appear , the DSC and handbrake light were on, but no ABS light. On scannning we found the following code 5E24 Pressure sensors, Next step was to view live data. under the live data options we checked the pressure sensor no1 circuit and pressure sensor no2 circuit and also the brake fluid monitor. First results were as expected apart from the brake fluid which showed, “NOT OK”. Circuit No1 was around 1 bar which was fine as was No2 circuit which was running similar data to No1 circuit.

Next step:

Change brake fluid..

After running about 2 lts of Dot 4 through the system we tested the system again with the GD860. Results were much the same with the only noticeable difference being the brake fluid data changed from “NOT OK to “OK once the brake pedal was applied. Sensors were reading around 1 bar +- 0.6 bar. Then we cleared the stored codes.

Next step: Test drive approx 1 mile

Once returned from the test drive I rescanned the ABS and there were no codes stored, but had a look at the live data from the pressure sensors, Circuit No1 was same as before, hovering around 1 bar but Circuit No2 was high showing a reading of approx 20 bar +- 0.5  which without any pressure on the brake pedal was too high, and sure enough the DSC and handbrake light appeared while I was monitoring the pressure sensors. Not knowing which system was which I was able to squeeze my hand down into the space where the pressure sensors are mounted on the brake master cylinder and disconnect the front plug, which as it turns out was the Circuit No 2 sensor, the faulty one.

First I checked and cleaned the plug with contact cleaner but on monitoring the data on the GD860 it did not show any noticable difference,

Next step:

Replace the pressure sensor,  Circuit No2 is the one most forward on the brake master cylinder.

Replacement procedure:

  1. First off press the footbrake until it goes hard and all vacuum has gone for the servo. (Engine off and no ignition on)
  2. Remove the vacuum pipe from the Brake servo cylinder. it obstructs the access to the brake pipe flare nut above the No2 circuit pressure sensor
  3. Fill the brake master cylinder to capacity with DOT 4 fluid ( we recommend a full brake fluid change before replacing the pressure sensors)
  4. Remove the Brake pipe above the Pressure sensor where it exits the brake master cylinder, 11 mm flare wrench required
  5. Disconnect the faulty pressure sensor from the electricial plug, (depending on position you may be able to access this before removing the brake pipe.
  6. Using a 27mm open end spanner slacken the pressure sensor
  7. The next part need to be done quick so as to not let the master cylinder run dry as bleeding the master cylinder can be a pain
  8. Have the new sensor ready to screw in, once the faulty is removed quickly replace with the new sensor.
  9. Tighten the sensor and replace the brake pipe flare nut, refit the vacuum pipe to the servo unit, top up the brake fluid and if the system needs to be bled, usually all is required is to slacken the union from the master cylinder to the ABS housing and a pump or two is usually enough.
  10. Check all disturbed pipework is secure and not leaking, all electricial connections are replaced, and fluid levels are correct.
  11. Now when you go to live data the readings should stay pretty much similar and the lights on the dash will remain off..

For Bmw diagnostic tools check out: http://www.scantool-direct.co.uk

 

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