Cruise Control: Description and Operation

CRUISE CONTROL

CIRCUIT OPERATION

Petrol Engine
For vehicles equipped with a manual 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 clutch pedal is not depressed. Also, the BeCM (Z238) will deactivate cruise control if the engine rpm rises above 5000±10%, due to the possibility of selecting gears manually without the use of the clutch.

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 C1279/Pin 14 of the BeCM (Z238).The BeCM (Z238) then supplies signal voltage via its Pin 18 to the Converter/Inverter (Z249), to Pin 8 of the Cruise Control ECU (Z121) and to the "Operation" bulb of the Cruise Control Switch (X115). The transfer gearbox Hi range status from the Transfer Gear Box ECU (Z256) is applied to C1287/Pin 3 of the BeCM (Z238). The X, Y, and Z switch status (PRND321 position information) from the gearbox position switch is applied to C1287/Pins 8, 9, and 18 of the BeCM (Z238). The clutch pedal position input is applied to C1279/Pin 4 and the engine speed input C1288/Pin 9 of the BeCM (Z238). When the transfer gearbox is in Hi range, a forward gear is selected and the Cruise Control Switch (X115) is on, the BeCM (Z238)supplies voltage via C1276/Pin 1 and the Brake Switch Vent Valve (X112) to the Cruise Control ECU (Z121) Pin 1, which then "knows" that cruise control can be operated.

When cruise control is activated and a cruise speed is set, the Cruise Control ECU (Z121) applies voltage through the OU wire and ground through the OR wire to operate the Cruise Control Vacuum Pump (M103) motor. The Cruise Control ECU (Z121) applies ground through the OK wire to close the normally open solenoid valve in the pump. The pump applies vacuum to the actuator.

SET/ACCEL
To set a cruise speed, the Cruise Control Switch (X115) must be on and vehicle speed must exceed 28 mph (45 km/h). When the SET/ACCEL Switch is depressed under these conditions, the Converter/Inverter (Z249) is supplied with a ground signal. This signal is "converted" to a voltage signal and is transmitted via the SY wire to the Cruise Control ECU (Z121) terminal 4, causing the vacuum pump to operate. When the SET/ACCEL Switch is released, the signal is removed from terminal 4, signalling the ECU to set the speed.

RES/DECEL
When the RES/DECEL Switch is depressed, a signal is applied via the RY wire to terminal 2 of the Cruise Control ECU (Z121). This tells the ECU (Z121) to disengage the system and the vehicle slows down. When the switch is depressed a second time, the signal is again applied to the ECU (Z121) and the vehicle returns to the previously set speed.

Speed Input
Terminal 15 of the Cruise Control ECU (Z121) receives the Vehicle Speed output signal from the BeCM (Z238) through the Y or YR wire. The BeCM (Z238) receives the vehicle speed signal from the Anti-lock Brake System ECU (Z108). The signal is a pulsing voltage and its frequency changes with vehicle speed.

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 1 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 Transmission).
- The engine rpm rises above 5000±10% (Manual Transmission).

The BeCM (Z238), which monitors these signals, will then remove power from C1279/Pin 18.

Road Test

CAUTION: DO NOT ENGAGE CRUISE CONTROL WHEN VEHICLE IS BEING USED IN LOW TRANSFER GEARS.

WARNING: The use of cruise control is not recommended on winding, snow covered or slippery roads, or in heavy traffic conditions where constant speed cannot be maintained.

1. Start the engine and depress the Cruise Control Switch (X115) to activate the cruise control system. Accelerate to approximately 30 mph (50 km/h) and press the SET/ACCEL Switch. Immediately release the switch and remove foot from the accelerator pedal. The vehicle should maintain the speed at which the SET/ACCEL Switch was pressed.
2. Press the SET/ACCEL Switch and hold at that position. The vehicle should accelerate smoothly until the switch is released. The vehicle should now maintain the new speed at which the SET/ACCEL Switch was released.
3. Press the RES/DECEL Switch while the vehicle is in the cruise control mode. The cruise control should disengage. Slow to approximately 35 mph (55 km/h) and press the RES/DECEL Switch. Immediately release the switch and remove foot from the accelerator. The vehicle should smoothly accelerate to the previously set speed. Increase speed using the accelerator pedal. Releasing the pedal should return the vehicle to the previously set speed.
4. Depressing the brake pedal should immediately disengage the cruise control system and return the vehicle to driver s control at accelerator pedal. Press the RES/DECEL Switch and the vehicle should accelerate to the previously set speed without operation of the accelerator pedal.
5. Press the RES/DECEL Switch and allow the vehicle to decelerate to below 26 mph (42 km/h). Press the RES/DECEL Switch and remove foot from the accelerator pedal. The vehicle should smoothly adjust to the previously memorized speed.
6. Press the SET/ACCEL Switch below 28 mph (45km/h) and the cruise control system should remain disengaged. Accelerate the vehicle above 28 mph (45 km/h), press the RES/DECEL Switch and remove foot from the accelerator pedal. The vehicle should smoothly adjust to the previously memorized speed.
7. Pressing the Cruise Control Switch (X115) should immediately disengage the cruise control system and erase the previously set speed from Cruise Control ECU (Z121)/Engine Control Module (ECM) (Z132) memory.