Steering Control Module: Description and Operation
MODULE-STEERING CONTROLDESCRIPTION
WARNING: The Steering Control Module (SCM) must be replaced in the event of a frontal impact event where the front airbags have been deployed. The clockspring is integral to the SCM and is not reusable.
This vehicle is equipped with a Steering Control Module (SCM) that houses an integral clockspring. It is an interface for switches such as ignition, lighting, wipers, horn, speed control, and remote radio. The SCM receives switch input and either directly sends or buses the outputs to the proper destinations. The module communicates via the Controller Area Network (CAN) B data bus. If the vehicle is equipped with ESP, the module is equipped with a steering angle sensor. Steering angle data is sent over the CAN C data bus.
The Steering Control Module (SCM) is mounted to the steering column shaft. The SCM is located under the steering column shroud and is attached to the steering column with two screws at the upper portion of the module. A key on the cancel cam indexes with a keyway on the steering shaft. There are five electrical connections on the column side of the SCM. The module connects to the vehicles wiring harness with two connectors; a 4-way which is a pass through for the airbag squids, and a 16-way. The other three connectors are for the hazard and multi-function switches and are concealed when the switches are in place. Any switched input that would cause a vehicle system to function that does not require that the key be ON, such as turning on the lights or sounding the horn, prompts the SCM to wake up on the CAN data bus network. If equipped with ESP the steering angle sensor must be recalibrated using the scan tool.
The components that are contained within or attach to the SCM are:
^ Clockspring - The clockspring is integral to and serviced as a unit with the Steering Control Module (SCM).
^ Connectors - The steering wheel side of the SCM contains four connectors. These consist of a 2-way, a 6-way and two squib connectors. Two short harnesses connect the steering wheel mounted airbag to the clockspring. These circuits pass directly through the SCM and are connected to the vehicle wiring at the 4-way connector located on the column side of the module. These circuits are directly connected to the ORC. The 6-way connector contains the horn signal and horn return circuits. The horn is an input to the SCM. The SCM receives the switch input and sends a bussed message over CAN B Bus. The 6-way connector also contains 2-speed control sense circuits and a speed control sense return. These circuits pass through and go directly to the PCM.
^ Hazard Switch - The hazard switch is located on the column side of the SCM. The FCM provides a 12-volt sense to the hazard switch. When the hazard switch is latched ON the sense circuit is connected to ground. Pulling the sense circuit voltage low indicates a request for hazard operation. The hazard switch is attached to the SCM using locking tabs and ears and can be serviced separately.
^ Ignition switch - The ignition switch is a combination of direct power feed and a position sensor. The SCM sends a 5-volt reference to the MUX portion of the switch. The SCM determines switch positions and sends this information over the CAN B Bus. The ignition sense inputs to the SCM are ignition switch sense (MUX reference) and ignition switch sense return. The SCM "decodes" the ignition switch status input to determine the current position of the ignition switch because the switch is a resistive MUX component. The voltage values of the ignition switch changes depending on the position of the switch.
^ Left Multi-Function Switch - The left multi-function stalk contains the lighting functions, high beams, turn signals, park lamps, fog lamps, interior lights and panel dimmer. It is a MUX type switch and is connected to the SCM using an 11-way connector. All outputs form the left multi-function switch are bused from the SCM. The left multi-function switch can be serviced separately. It attaches to the SCM using a combination of locking tabs and two screws.
^ Right Multi-Function Switch - The right multi-function stalk contains the front and rear wiper and washer functions. It is a MUX-type switch and is connected to the SCM using a 9-way connector. All outputs from the right multi-function switch are bused from the SCM except the Rear Wiper On signal and the Rear Wiper Delay signal. These are controlled by high side drivers in the SCM based on MUX inputs. They are direct inputs to the rear wiper motor. The right multi-function switch can be serviced separately. It attaches to the SCM using a combination of locking tabs and two screws.
^ Steering wheel mounted switches - Steering wheel mounted remote radio controls use MUX type switches. A MUX signal and a return circuit connect to the SCM at the 2-way connector. The SCM receives the switch input and sends a bussed message over CAN B Bus.
* Steering Angle Hall Effect Sensor (if equipped with Electronic Stability Program (ESP) - The SCM contains an additional Hall Effect sensor which is driven off the steering shaft. A 51-tooth gear attached to the data wheel drives an 18-tooth gear containing magnets. (0.35 to 1 ratio) These magnets change the magnetic field surrounding the Hall sensors as the steering wheel is rotated. Determining if the clockspring is centered is possible by observing the scan tool. Steering wheel position is displayed as "Angle" with a range of up to + 900 degrees. Since the SCM determines the position from the data of both sensors, the SCM does not have to be initialized following a battery disconnect. Steering angle information is sent over the CAN C Bus.
^ Steering Angle Sensor (if equipped with Electronic Stability Program (ESP) - Vehicles equipped with ESP use a steering angle sensor. The sensor is internal to the SCM and cannot be serviced separately. As the steering wheel is rotated an internal data wheel or code disc interrupts infrared light beams. Optic clusters containing three rows of four light detectors, determine steering wheel position based on which beams are interrupted and which are not. The SCM can also distinguish all steering wheel position from lock to lock.
NOTE: Vehicles using Electronic Throttle Control (ETC) use a second (redundant) speed control sense circuit.
The following components can be serviced separately.
^ Hazard Switch (2)
^ Right Multi-Function (wiper/washer) Switch (3)
^ Left Multi-Function (lighting control) Switch (1)
^ Cancel Cam
^ Steering Angle Sensor (if equipped with Electronic Stability Program (ESP))
^ Steering Control Module (SCM) with integral clockspring (4)
OPERATION
The Steering Control Module (SCM) is connected to a battery feed and ground. It receives battery power on Cavity 8 of the 16-way Connector from the A108 circuit. It is protected by a 10 Amp fuse in Cavity 16 of the Junction Block. It receives ground at Cavity 5 of the 16-way Connector, which is grounded on the Z907 circuit.