Actuator Failure Modes
The cruise control actuator will seem to work only intermittently or
partially when a tooth is broken in the gear driving the control belt
drum. This is because the control unit will attempt to operate the
actuator, but gets inconsistent feedback from the potentiometer when
the drive encounters the broken tooth.
Figure 1 - Control belt drum with broken tooth
When the inconsistent feedback is received the control unit will
eventually give up and disengage. A similar effect is noticed when the
potentiometer resistance surface or wipers become pitted or burned.
When the control belt breaks or the motor or solenoid burns out a
complete failure of the actuator is observed.
BMW Cruise Control Actuator 1985 to 1996 – Technical Data page 6 of 25
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