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Tahoe / Yukon Service Manual

Steering Wheel and Column Description and Operation

Column Lock The Column Lock Module (CLM) controls the steering wheel theft deterrent lock function, which allows the column to be electronically locked. When a valid key is used to start the vehicle, the BCM recognizes this and will send the encrypted password to the CLM. The CLM will compare its own stored password to the encrypted password sent by the BCM. If the data matches, the steering column will be unlocked. In order for the steering column to be locked the CLM has to see 3 inputs.

  1. The BCM power mode is OFF.
  2. The vehicle is stationary based on zero speed reported from all ABS wheel speed sensors.
  3. The driver or passenger door is opened reported by the PEPS module. When the CLM receives these inputs, the steering column will be locked. The CLM monitors the column lock system and will set DTC codes when the module detects malfunctions within the system. When a malfunction occurs the driver information center (DIC) will display the Service Column Lock Now message indicating DTC codes are set within the CLM. The immobilizer system will prevent vehicle starting if there is a fault or no communication with the CLM. Tilt/Telescoping Description The steering column has a tilt/telescoping control system that consists of an electronic control module capable of LIN message communication, a steering column power assembly with positioning actuators and sensors, and a steering column control switch. Column Position Module has two versions of operation:
  4. N38 – Power Steering Column-Tilt/Telescope, and A45 – Memory Seats The column position module will wake up either by the LIN bus or by the tilt/telescope steering column switch. The memory seat module is the master and column position module is the slave. All DTCs and the data from column position module are reported through the LIN bus and stored in the memory seat module.
  5. N38 – Power Steering Column-Tilt/Telescope Only The column position module will wake up with the tilt/telescope steering column switch. No DTCs or data is available. Vehicle symptoms will cause the customer to bring the vehicle in for service. Tilt/Telescoping Switch Operation The tilt/telescope steering column has a four-position switch. The switch may be used to adjust the position of the steering wheel in or out which is telescope and up or down which is tilt. The position of the column may be changed as follows: Press the switch up to tilt the column up. Press the switch down to tilt the column down. Press the switch forward and the column moves toward the front of the vehicle. Press the switch rearward and the column moves toward the rear of the vehicle. Actuators Both the tilt and telescoping actuators are reversible. For example, the tilt actuator moves the column both up and down. When the column position module receives an input to move the column up, the column position module supplies battery positive voltage and ground to the tilt actuator in order to move the column up. When the column position module receives a column down input, the column position module supplies battery positive voltage and ground to the same actuator, but with reverse polarity. When the voltage polarity is reversed, the actuator runs in the opposite direction and moves the column down. Position Sensors with A45 Memory Seats Two position sensors are Hall Effect sensors and are used by the column position module. The column position module provides a 5 V reference voltage and a ground to both the tilt and telescoping position sensors. The sensor feedback circuit voltage varies from 0–5 V. Each sensor is part of the actuator assembly. When the actuator rotates, the voltage of the sensor varies on the scan tool. The column position module monitors the feedback voltage to determine the column position. Without the A45 Memory Seat option, scan tool data is not available. Tilt/Telescoping Memory with A45 Memory Seats Memory settings and the personalization of steering wheel positions are available with the tilt/telescoping steering column only with the A45 Memory Seat option. The data stored consists of entry positions and exit positions. The entry position is the position that the steering column moves in when the ignition is turned ON. The exit position is the direction that the steering column moves in when the ignition is turned OFF and the driver’s door is opened. The memory seat module stores memory positions and commands column position module to move actuators to specific positions through a LIN message. An initial memory setting is set in the memory seat module at the assembly plant. This setting may be changed by the customer at any time. Without the A45 Memory Seat option, memory settings, personalization, and the entry and exit function is not available. Driver Safety The steering wheel and column has safety features to protect the driver. The following components may be mounted on or near the steering column: Energy-Absorbing Steering Column: The energy-absorbing steering column compresses in the event of a front-end collision, which reduces the chance of injury to the driver. The energy- absorbing feature, collapsible steering shaft, and break away mounting features help reduce the injury in the event of an accident. Heated Steering Wheel The heated steering wheel system consists of a heated steering wheel, a heated steering wheel switch, and a steering wheel heat module. The heated steering wheel includes non-serviceable heating elements and a temperature sensor. The heating elements and sensor are located in the left and right sides of the rim of the steering wheel. The heated steering wheel switch is located in the left steering wheel control switch assembly. The steering wheel heat control module is located at the bottom of the steering wheel center hub. When the switch is pressed, the switch signal circuit is grounded and the heat module turns the heated steering wheel on. The system then remains on until the customer turns it off. The wheels normal operating temperature is 32°C (89.6°F). The wheel takes approximately 3 to 4 minutes to reach the normal operating temperature. The wheel will take longer to heat up if the vehicle temperature is below -21°C (-5.8°F). The built-in temperature sensor provides input to the controller to limit the temperature to the normal operating temperature. The wheel will not operate if the vehicle temperature is at or above 32°C (89.6°F). The heated steering wheel control module is on the LIN bus. This allows the heated steering wheel to be activated during remote vehicle start.