C2.2 Trionic
To checkCheck whether the tone comes from the PWM control of the idle air control valve, as follows:
1. Start the engine and switch on the radio.
2. Unplug the connector from the idle air control valve in the engine bay. The tone should now disappear.
Procedure
The fault can be rectified by fitting interference suppression kit 48 72 685 (CA=30567466) as described below:
1. Remove the Trionic control module as described in group 2 "Trionic".
2. Unplug the connector and extract the pin at position 49 (red/blue lead).
3. Cut off the terminal.
4. Cut all but 200 mm (8 in.) off the interference suppression capacitor's lead.
5. Crimp the red/blue lead together with the interference suppression capacitor's lead in a new connector.
6. Refit the new pin in position 49 of the connector.
7. Plug in the connector.
8. Mount the capacitor on the left-hand screw at grounding point G34.
9. Check the result of the above measures by starting the car and switching on the radio.