Engine management system - siemens (all except NAS) (Cancelling): Description and operation

Suspend When the RES switch is pressed, the cruise control ECU disconnects the pump and valve power supply output from the vacuum pump, EAT ECU and instrument pack. The set speed is retained in memory by the interface ECU. When the pump and valve power supply is disconnected: l The vacuum pump assembly vents the vacuum actuator and control of the throttle returns to the accelerator pedal. l The EAT ECU returns to its previous operating mode. l The cruise control warning lamp in the instrument pack is extinguished.

If the interface ECU or the ECM suspend cruise control, the power supply from the interface ECU to the cruise control ECU is disconnected. Since the power supply is used to operate the vacuum pump assembly, system operation is automatically suspended. If the cruise control ECU detects the brakes being applied, it disconnects the pump and valve power supply output even if the power supply from the interface ECU is still present.

Resume Provided the system is enabled, pressing the RES switch causes the cruise control ECU to output the pump and valve power supply to resume operation of the vacuum pump assembly and accelerate or decelerate the vehicle to the stored set speed. The EAT ECU returns to the cruise control mode and the cruise control warning lamp in the instrument pack illuminates.

Cancelling

Cruise control is cancelled by pressing the master switch. When cruise control is cancelled, the LED in the master switch extinguishes and the power feeds from the switch to the cruise control ECU and the interface ECU are disconnected. The set speed is lost from the memory of the cruise control ECU and the power supply from the interface ECU to the cruise control ECU is disconnected. If cruise control is engaged when the master switch is pressed: l The cruise control ECU stops operating the vacuum pump assembly and control of the throttle returns to the accelerator pedal. l The EAT ECU returns to its previous operating mode. l The cruise control warning lamp in the instrument pack is extinguished.

Diagnostics

While the system is active, the cruise control ECU performs self-checks and plausibility checks of the outputs to the vacuum pump assembly and the input from the brake pedal position sensor. If a fault is detected, a related fault code is stored in the non volatile memory of the cruise control ECU and cruise control is disabled for the remainder of the ignition cycle. Codes are retrieved using TestBook, which communicates with the cruise control ECU via an ISO 9141 K line connection from the diagnostic socket.

The interface ECU monitors the two inputs from the brake pedal position sensor and disables cruise control for the remainder of the ignition cycle if a fault is detected. The interface ECU can detect open circuits and implausible inputs. However, simultaneous short circuits to 0 or 12 volts in both inputs cannot be detected and, if this occurs, cruise control operates but does not suspend operation when the brake pedal is pressed.

The system is reset at the beginning of each ignition cycle and operates normally if a previously detected fault is no longer present.