System Disable

The cruise control system can be disabled in one of four ways:
1. 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.
2. The RES/DECEL Switch is depressed, signalling the Cruise Control ECU (Z121) via the Inverter/Converter (Z249) to disengage the system.
3. 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.
4. 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 deenergize 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 Transmission).
- The engine rpm rises above 5000 + 10% (Manual Transmission).

The BeCM (Z238), which monitors these signals, will then remove power from C255/Pin 18.