Cruise Control Pump

Engine Control Module (ECM) The ECM (C0371) provides a feed to the interface unit (C1959) on a BU wire if the following conditions exist:

HDC is not activated. The gear selector lever is not in the park, neutral, or reverse positions. Engine speed is below 6,496 rpm.

For more information on the Siemens ECM, refer to the Engine Management Systems – Siemens section of the System Description and Operation Workshop manual.

Cruise Control Pump

When all conditions for cruise control activation have been met, the cruise control ECU (C0239) provides a feed to the cruise control pump motor (C0228) on a WU wire. The pump motor creates a vacuum in the pump actuator. For a detailed description of actuator operation, refer to the Engine Management Systems – Siemens section of the Workshop manual.

Current flow across the pump motor is controlled by the ECU (C0239) providing a varying Pulse Width Modulated (PWM) signal to the other side of the pump motor (C0228) on a BR wire. When the correct vehicle speed has been reached, the ECU (C0239) replaces the PWM feed with a continuous feed. As the potential difference across the pump motor is now 0V, the pump motor stops operating.

To maintain the vacuum in the actuator, both the control and dump valves are closed by the ECU. To close the valves, the ECU (C0239) provides a feed to the control and dump valves (C0228) on a WU wire. Current flows across the control valve (C0228) to the ECU (C0239) on a PY wire. Current flows across the dump valve (C0228) to the ECU (C0239) on a BR wire.

NOTE: Both the control valve and the dump valve are normally open valves.

When a decrease in speed is requested, the control valve is opened to reduce the depression within the actuator. This is done by the ECU (C0239) providing a PWM signal to the control valve (C0228) on a PY wire. When the correct speed has been achieved, the PWM signal is withdrawn.

When cruise is cancelled, the ECU (C0239) withdraws the feed to the dump valve (C0228) on a WU wire. The dump valve now opens, allowing atmospheric pressure into the actuator.

Brake Pedal Switch

As a safety feature, the dump valve is opened if the brake pedal is depressed. If cruise control is active and the brake pedal is pressed, the brake pedal switch (C0075) provides a feed to the dump valve (C0228) on a GP wire. As the potential difference across the valve is 0V, the valve opens allowing atmospheric pressure into the actuator.