C2. Background Tone: Overview

A tone can be generated by three different systems. They are easy to distinguish from each other, depending on when the tone occurs.

1. The background tone varies between different stations and it comes and goes according to the light intensity sensed by the photodiode in the SID.

The fault can show up on M94 and later cars and is caused by the main instrument 2. An interference-suppressed processor card has been introduced on the types of instrument displays below as of the following chassis numbers:

- miles/turbo T2034392 and T7007538 respectively

- miles/inj T2035029 and T7008509 respectively

- km/turbo: not introduced at the time of this SI's publication

- km/inj: not introduced at the time of this SI's publication

See section 02.1 for checking and rectification.

2. A steady howling tone which disappears 5 seconds after the ignition is switched off.

The fault occurs on cars equipped with Trionic M94-.

See section 02.2 for checking and rectification.

3. A tone occurs when the lights dim after the door has been closed.

The fault is due to the ICE and occurs on M94- cars.

See section 02.3 for checking and rectification.