Variable Effort Steering System Cadillac XLR I

Steering Assist Schematic Icons

Steering Assist Schematic Icons Icon Icon Definition IMPORTANT: Twisted-pair wires provide an effective shield that helps protect sensitive electronic components from electrical interference. If the wires were covered with shielding, install new shielding. In order to prevent electrical interference from degrading the performance of the connected components, you must maintain the proper specification when making any repairs to the twisted-pair wires shown : The wires must be twisted a minimum of 9 turns per 31 cm (12 in) as measured anywhere along the length of the wires The outside diameter of the twisted wires must not exceed 6.0 mm (0.25 in)

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Steering Assist Connector End Views

Variable Effort Steering Actuator

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Steering Assist Connector End Views

Steering Wheel Position Sensor

Diagnostic Starting Point - Variable Effort Steering

Begin the system diagnosis with the Diagnostic System Check - Vehicle . The Diagnostic System Check will provide the following information

1. The identification of the control modules which command the system
2. The ability of the control modules to communicate through the serial data circuit
3. The identification of any stored DTCs and their status

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and where the procedure is located.

Scan Tool Data List

Electronic Brake Control Module (EBCM)

Circuit Description

The variable effort steering (VES) system uses the electronic brake control module (EBCM) to control current to a bi-directional electromagnetic rotary actuator. The EBCM commands current from negative 3 amps to positive 3 amps to the actuator. At low speeds, less than approximately 24 km/h (15 mph), negative three amps of current is commanded, providing maximum assist to steering. As speed increases, increased (more positive) current is commanded, reaching zero amps at approximately 96 km/h (60 mph). The EBCM commands positive current only during steering input at higher speeds, based on the above inputs and the vehicle calibration, which creates steering resistance.

DTC Descriptor

This diagnostic procedure supports the following DTC

DTC C0450 Steering Assist Control Solenoid/Motor/Actuator Circuit

Conditions for Running the DTC

1. Ignition voltage between 10.5-17 volts
2. Off state test-Initial ignition ON, no engine RPM or vehicle speed present.
3. On state test-If off state test passes, engine RPM and vehicle speed present.

Conditions for Setting the DTC

An open, short to ground, or short to voltage in the VES actuator or the circuits to the actuator

Action Taken When the DTC Sets

1. DTC C0450 is stored in memory.
2. The driver information center (DIC) displays the SERVICE STEERING SYSTEM warning message.
3. The VES system is disabled for the remainder of the ignition cycle.

Conditions for Clearing the DTC

1. A current DTC will clear when the malfunction is no longer present.
2. A history DTC will clear after 100 ignition cycles.

Diagnostic Aids

The vehicle may need to be driven to view full VES Actuator Commanded and Actuator Feedback Data parameters.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. 2: This step tests if the Actuator Commanded and Actuator Feedback Current parameters are within specification in their active state.
2. 3: Perform the VES test located under Special Functions. This test may indicate if the VES actuator is mechanically bound.
3. 4: This step tests if the resistance of the VES actuator is within specification.
4. 7: This step tests the control circuit of the VES actuator for a short to ground.
5. 13: Perform the setup procedure after EBCM replacement.

DTC C0450

The Variable Effort Steering (VES) system, or MAGNASTEER II® varies the amount of effort required to steer the vehicle as vehicle speed changes or lateral acceleration occurs. At low speeds, the system provides minimal steering effort for easy turning and parking maneuvers. At high speeds, the system provides firmer steering (road feel) and directional stability. When the system senses lateral acceleration, steering becomes firmer to reduce oversteering. The Electronic Brake Control Module (EBCM) controls a bi-directional magnetic rotary actuator located in the steering rack and pinion. The EBCM varies the steering assist by adjusting the current flow through the actuator. The actuator adjusts the amount of power steering assist to achieve a given level of effort to steer the vehicle. The VES system accomplishes this by adding or subtracting torque on the input shaft to the rack and pinion. The main component of the system is an electromagnetic actuator, which consists of a multiple-pole ring-style permanent magnet, a pole piece, and an electromagnetic coil assembly. The VES system uses the Antilock Brake System (ABS) wheel speed sensor inputs to determine vehicle speed. When the EBCM senses vehicle speed, it commands a current to the actuator that is most appropriate for each speed. The system also uses inputs such as Handwheel position, wheelbase, understeer coefficient and steering ratio to calculate lateral acceleration. The EBCM commands current from negative two amps to positive three amps to the actuator, which is polarized. At low speeds, a negative current is commanded, which assists steering. At medium speeds, no current is commanded and steering is assisted by hydraulics only. At high speeds, a positive current is commanded, which creates steering resistance. Ignition voltage and ground are provided through the EBCM. The EBCM has the ability to detect malfunctions in the actuator or the circuitry to the actuator. Any malfunctions detected will cause the system to ramp to zero amps and steering will be assisted by hydraulics only.

See also:
• Diagnostic System Check - Vehicle
• Testing for Intermittent Conditions and Poor Connections
• Testing for Short to Ground
• Wiring Repairs
• Circuit Testing
• Connector Repairs
• Control Module References
• Steering Gear Replacement
• Steering Assist Schematics