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Cruisin’ for a Fixin’.
Diagnosing, Troubleshooting and Repairing the Adaptive Cruise Control
Cruise control allows the driver to set their vehicle to maintain a specific speed. This feature is commonly used on the highway to relieve some of the physical pressure of a long road trip. It’s a bit like autopilot, but you still have to steer. When a slower vehicle is encountered, cruise control must be disengaged to slow the vehicle and prevent a collision.
Adaptive cruise control takes this helpful feature to the next level. In addition to setting a specific speed for the vehicle, it enables the vehicle to slow down automatically when approaching a slower car ahead. As an added feature, the driver can select the minimum distance to be maintained between themselves and the slower car.
Adaptive Cruise Control Basics
The adaptive cruise control (ACC) system uses a radar sensor that is mounted at the front of the vehicle, located in the lower portion of the front fascia, to detect objects in its path (see Figure 1). If the lane ahead of the vehicle is clear, the ACC system will maintain the set speed. When a slower vehicle ahead is detected, the vehicle speed will be adjusted to maintain the desired safe distance.
The ACC system operates down to 0 mph, which allows it to stop the vehicle, then re-engage to safe-range speeds as traffic begins to move. Adaptive speed control is resumed when the driver taps the accelerator, or presses the resume button.
The adaptive speed control system includes the ACC module, the anti-lock brake system (ABS) module, the brake lamp sensor, the speed control switch pod, the electronic vehicle information center (EVIC), the instrument panel cluster (when the speed control system is on, CRUISE is displayed), the powertrain control module (PCM), the transmission control module (TCM), the
steering column control module (SCCM) and the wheel speed sensors.
The driver controls all ACC system features through the speed control switch pod on the face of the right-hand spoke of the steering wheel (see Figure 2). There are eight push buttons on the pod. The top five push buttons are conventional speed control push buttons that are found on vehicles with conventional speed control and adaptive speed control. The three push buttons on the lower section of the pod are used exclusively for adaptive speed control.
In Figure 2, the adaptive speed control push buttons are labeled 1, 2 and 3. Push button 1 allows the driver to select between conventional and adaptive speed control. Push buttons 2 and 3 can be used to select the separation distance between the vehicle being driven and other cars within a matter of seconds. Press push button 2 to decrease the time between vehicles, or press push button 3 to increase the distance between vehicles. The range of distance separation is 1.0 to 2.0 seconds. Behind the scenes, the ACC module sends electronic message outputs to the ABS module, the TCM and the PCM to maintain the selected separation distance.
Troubleshooting the ACC System
Many component systems are inter-related with other systems within the vehicle. The adaptive speed control system is no exception. For example, the PCM plays a major role in the operation of the adaptive speed control system. If the PCM detects a fault on one of the following systems, it will disable the cruise control system and the appropriate Diagnostic Trouble Code (DTC) will be set and stored:
1. Engine speed sensor
2. Electric throttle sensor or actuators
3. Accelerator pedal potentiometer
4. Brake pedal position
5. Clutch switch rationality
6. Engine load sensor
7. Ignition coils
8. Fuel injectors
9. Turbo sensors or actuators
The PCM and ACC modules continuously monitor all of the speed control electrical circuits to determine the system readiness and accuracy. If a monitored system fault is detected, a Diagnostic Trouble Code (DTC) is set and stored. The PCM and ACC components use On-Board Diagnostics (OBD) and can communicate with other electronic modules, the diagnostic scan tool using the CAN data bus. Hardwired inputs and outputs for the PCM and ACC module can be diagnosed using conventional diagnostic tools and procedures.
The adaptive speed control system has proven to be dependable and reliable. Those vehicle owners who use adaptive speed control have found it to be a very desirable option that enhances the driving experience, especially on long road trips. From time-to-time, because of the nature of its push button design, the speed control switch pod can malfunction. When this occurs, the entire pod must be replaced.
Speed Control Switch Pod Replacement
Because the speed control switch pod is mounted on the steering wheel, the supplemental restraint system (SRS), commonly known as the airbag system, must be disabled. So, disconnect and isolate the negative battery cable, then wait two minutes before proceeding with any service work. This waiting period allows the system capacitor to discharge.
Before beginning service on the speed control switch pod, remove the driver airbag from the steering wheel. On the back of the steering wheel, remove the remote radio switch cover. This is done by inserting a small, fl at screwdriver into the slot on the cover and prying. With the cover off, remove the switch retaining screw, then the switch. This will expose the steering wheel bezel retaining screw. Remove this screw to remove the steering wheel bezel. Some vehicles might have two bezel retaining screws.
With the bezel off, remove the upper switch retaining screw, located to the upper left of the speed control switch pod. Disconnect the electrical connector from the switch pod, then remove the speed control switch pod.
To install the new speed control switch pod, connect the wiring harness to the switch pod and seat it in the steering wheel. Install and tighten the upper switch retaining screw. Position the steering wheel bezel in place, then on the backside, install and tighten the steering wheel bezel retaining screws.
Install the remote radio switch, then install and tighten the switch retaining screw. Next, install the remote radio switch cover. To finish the replacement procedure, re-install the driver airbag.