Cruise control – circuit operation

CRUISE CONTROL – CIRCUIT OPERATION

System Disable

The cruise control system can be disabled in one of four ways: 8. The Cruise Control Switch (X115) is put in the 0 position, removing the BeCM (Z238) power from the Cruise Control ECU (Z121) and vacuum pump, and erasing the set speed memory. 9. The RES/DECEL Switch is depressed, signalling the Cruise Control ECU (Z121) via the Inverter/ Converter (Z249) to disengage the system. 10. The brake pedal is depressed and a vacuum valve in the Switch Vent Valve opens (X112). This vents vacuum to the actuator valve and releases the throttle. 11. The Voltage applied to the Cruise Control ECU (Z121) terminal 9 is interrupted, causing the Cruise Control ECU (Z121) to turn off the vacuum pump and de-energize the vacuum solenoid valve. This voltage path is interrupted when: The brake pedal is depressed. With the brake
pedal depressed, the Brake Switch Vent Valve (X112) moves to position 1 and the circuit is interrupted. The transfer gear box is not in Hi range.
The vehicle speed does not exceed 28 mph (45
km/h). The vehicle is not in a forward gear (P, R, or N)
(Automatic Transmission). The clutch pedal is depressed (Manual Trans
mission). The engine rpm rises above 5000 ± 10% (Ma
nual Transmission). The BeCM (Z238), which monitors these signals, will then remove power from C255/Pin 18.

Diesel Engine

For vehicles equipped with a manual transmission, cruise control can only be activated when the Cruise Control Switch (X115) is depressed and the clutch pedal is not depressed. The Diesel Engine Control Module (Z132) will not allow the engine to overspeed if a cruise control speed is requested that is beyond the capability of the engines speed range. For vehicles equipped with an automatic transmission, cruise control can only be activated when the Cruise Control Switch (X115) is depressed, the transfer gear box is in Hi range, and the transmission is in one of the forward gears.

With the Cruise Control Switch (X115) on, a ground signal is applied to C255/Pin 14 of the BeCM (Z238). The X, Y, and Z switch status (PRND321 position information) from the gearbox position switch is applied to C626/Pins 8, 9, and 18 of the BeCM (Z238). The clutch pedal position input is applied to C255/Pin 4 and the engine speed input is applied to C112/Pin 9 of the BeCM (Z238). The BeCM (Z238) then supplies voltage, via its Pin 18 to the Inverter/Converter (Z249) and to the “Operation” bulb of the Cruise Control Switch (X115). The Cruise Control Converter/Inverter Module (Z249) supplies the Engine Control Module (Z132) via its pin 4 with a voltage signal to “switch on” the cruise circuit. For the Diesel Engine, the Engine Control Module (Z132) controls the cruise circuit as the Cruise Control ECU (Z121) does for the Petrol Engine. The Engine Control Module (Z132) is also responsible for the acceleration/deceleration of the vehicle.