So in short. If the error comes and stais back the new servo is the ancer. Can you tell me more about vag com test ?
Hi,
The first thing I would do is check the wiring and connectors. It is possible for example that there may be corrosion on the connector pins.
The brake detection switch and solenoid are connected to by a 6 pin connector on the front of the vacuum reservoir as seen from the front of the car looking in the engine bay. The wiring goes straight from this connector to the ABS unit which is at the front right corner.
The electrical connections are as follows:
Servo pin
| Wire colour
| Function
| ABS pin
|
1
| blue / green
| Switch pole
| 13
|
2
| blue / red
| Switch pole
| 29
|
3
| blue / yellow
| Solenoid coil
| 1
|
4
| blue / purple
| Solenoid coil
| 17
|
5
| blue / black
| Switch common
| 32
|
The pins on the reservoir are easy to tell as the wires can be seen, but the ABS unit plug is not marked. The following diagram identifies the pin positions:
You can also check the solenoid and switch with a multi-meter set to measure resistance. The solenoid should be a low resistance (a few ohms, I can't remember the exact number) and the switch should be close to zero when closed on each side. If you check on the ABS plug side, you can check the switch, solenoid and wiring at the same time.
The solenoid valve test is performed using the "basic settings" option.
* Turn ignition on
* Connect to "ABS Brakes" number 03.
* Go to "Basic Settings" number 04.
* Enter group "031" then "Go!"
You should hear a "clunk" as the solenoid has been activated.
"Solenoid coil enabled" should be displayed.
* Click "Up" to go to group "032".
This displays the brake pressure sensor outputs and should say "not oper.".
The pressure should be low. (approx. -0.6bar)
* Click "Up" to go to group "033".
The display should say "press pedal and hold".
Depress the brake pedal with your foot and hold it.
When pressing the brake pedal, the brake lights should come on.
They should not have been on before as the brake light deactivation relay should have stopped them coming on when the ABS unit "applies" the brakes.
If the lights don’t come on then there is a problem with the relay J508 or the switch in the servo.
* Click "Up" to go to group "034"
The display should show the brake pressure output (about 30bar if you are pressing hard) and should say "Activated" if everything is working correctly.
* Click “Up” to go to group "035"
The display should say "pedal release"
Release the brake pedal.
* Click "Up" to go to group "036"
This displays the brake pressure (low value) and "not oper." if everything is OK.
* Click "Up” to go to group "037"
The display should say "solenoid coil test ended".
* Click "Up"
The test is finished. You should hear a "clonk" as the solenoid is released.
If everything goes as above with the same read-outs then the solenoid and switch are OK, at the point of testing.
I suspect that sometimes the switch does not change over at the right time or at all and this is detected as an intermittent fault. The above checked out OK on my car but it did fail to work correctly when driving occasionally which caused the "intermittent" class fault to be logged.
regards
Andrew