Cruise Control Systems: Description: Notes

WARNING: Vehicles are equipped with air bag supplemental restraint system. Before attempting any repairs involving steering column, instrument panel or related components, see SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR BAG SYSTEM in DAIMLERCHRYSLER CORP. - AIR BAG RESTRAINT SYSTEMS article in RESTRAINTS.

CAUTION: When battery is disconnected, vehicle computer and memory systems may lose memory data. Driveability problems may exist until computer systems have completed a relearn cycle.

WARNING: The use of speed control is not recommended when driving conditions do not permit maintaining a constant speed, such as in heavy traffic or on roads that are winding, icy, snow covered, or slippery.

The speed control system is electronically controlled and vacuum operated. The electronic control is integrated into the Powertrain Control Module (PCM). The electronic controls are integrated into the Powertrain Control Module (PCM), located in engine compartment on driver's side under the speed control servo.

Fig 1: Speed Control Circuit Schmatic

Courtesy of CHRYSLER CORP.

The controls are located on the steering wheel. The ON, OFF, and SET buttons are located on the left side of airbag module. The RESUME, ACCEL, SET andCOAST buttons are located on upper right side of airbag module. See Fig 2 . The system is designed to operate at speeds above 30 MPH (48 km/h).

When the speed control is activated by depressing the ON switch, the PCM allows a set speed to be stored in RAM for speed control. To store a set speed, depress and release the SET switch while the vehicle is moving at a speed between 30 and 85 MPH. In order for the speed control to engage, the brakes cannot be applied, nor can the gear selector be indicating the transmission in Park or Neutral. The speed control can be disengaged manually by:

Stepping on the brake pedal.
Depressing the OFF switch. (Turning the system off using OFF switch or turning off the ignition switch will erase the set speed stored).
Depressing the CANCEL switch.
Depressing the clutch pedal.

For added safety, the speed control system is programmed to disengage for any of the following conditions:

An indication of Park or Neutral.
A rapid increase of RPM (indicates that the clutch has been disengaged).
Excessive engine RPM (indicates that the transmission may be in low gear).
The speed signal increases at a rate of 10 MPH per second (indicates that the co-efficient of friction between road surface and tires is extremely low).
The speed signal decreases at a rate of 10 MPH per second (indicates that the vehicle may have decelerated at an extremely high rate).
If the actual speed is greater than 20 MPH over the set speed.

Once the speed control has been disengaged, depressing the RESUME switch when speed is greater than 25 MPH allows the vehicle to resume control to the target speed that was stored in the PCM. While the speed control is engaged, the driver can increase the vehicle speed by depressing the ACCEL switch. The new target speed is stored in the PCM when the ACCEL switch is released.

The PCM also has a "tap-up" feature in which target speed increases by 2 MPH for each momentary switch activation of the ACCEL switch. The PCM also provides a means to decelerate to a new lower target speed without disengaging speed control. Depress and hold the COAST switch until the desired speed is reached, then release the switch. PCM also has a "tap-down" feature in which the target speed decreases at 1 MPH for each momentary switch activation of the coast switch.

Fig 2: Identifying Speed Control Switches

Courtesy of CHRYSLER CORP.