Power steering failure
Tech Contributor
Joined: Oct 1999
Posts: 41,037
Likes: 9,801
From: Charlotte, NC (formerly Endicott, NY)
Do you mean the EBCM? The BCM doesn't have anything to do with the power steering effort. The EBCM provides a signal to the Magna Steer rack that determines how much steering boost is provided.
Here is a description of how it operates:
Variable Effort Steering System Description and Operation
Description
The variable assist magnetic steering system MAGNASTEER® varies the driver effort required to steer the vehicle as speed changes. At low speeds, the system requires minimum steering effort for easy turning and parking maneuvers. Steering effort is increased at higher speeds in order to provide the driver with firmer steering (road feel) and directional stability. The EBCM controls a bi-directional magnetic rotary solenoid. The solenoid is located in the steering gear. The EBCM varies the steering assist by adjusting the current flow through the solenoid. The solenoid adjusts the amount of power steering assist in order to achieve a given level of driver effort to turn the vehicle.
MAGNASTEER® accomplishes this by adding or subtracting torque on the rotary input shaft to the power rack and pinion. The amount of steering assist is dependent upon vehicle speed. As the vehicle speed increases, the following actions occur:
• The steering assist decreases.
• The driver effort increases.
As the vehicle speed decreases, the following actions occur:
• The steering assist increases.
• The driver effort decreases.
Operation
The variable effort steering (VES) system uses inputs from the ABS wheel speed sensors and steering wheel position sensor to the EBCM to determine the desired amount of power steering assist.
The power steering pump magnetic rotary actuator regulates power steering fluid flow. The EBCM can change the amount of current flowing through the actuator.
The EBCM has the ability to detect malfunctions in the steering wheel position sensor, the actuator or the circuitry to those components. Any malfunction detected will cause the power steering assist to remain at maximum with the pintle in its normally retracted position for all speeds.
When the system is operating normally, increasing the vehicle speed will decrease power steering assist, allowing the driver to have improved road feel and directional stability. When the EBCM steering wheel position sensor detects sudden steering maneuvers, the EBCM reduces the actuator current in order to provide maximum steering assist.
Circuit Operation
When the Electronic Brake Control Module (EBCM) commands the Magnasteer Actuator ON, B+ is supplied through the EBCM to the MAGNASTEER actuator . Ground/control for the MAGNASTEER actuator is provided through the EBCM to MAGNASTEER actuator controls the amount of current supplied to the MAGNASTEER actuator based on the input from the wheel speed sensors.
VES Actuator
At the heart of the system is an electromagnetic actuator, which consists of a multiple-pole ring-style permanent magnet (that is attached to, and rotates with, the spool shaft or the input side of the system), a pole piece (that is attached to, and rotates with, the pinion or the output side of the system), and an electromagnetic coil assembly.
When the electronic controller senses the vehicle's speed, it generates an electrical current that is most appropriate for each speed. This current then energizes the electromagnetic coil, which causes the permanent magnet to seek alignment in relationship to the pole piece. (Note: Field strength increases with a higher current to increase the relative force between the permanent magnet and the pole piece.) Again, depending on the polarity of the current in the coil, the system, the current immediately ramps to 0 amps to provide a mid-range effort level. (Note: Currently, the principal input into the controller is vehicle speed. Other inputs may be added, such as steering wheel position, to derive lateral acceleration).
Use the DIC controls on the right side of the instrument panel to open the On Board Diagnostics and see if you have a C1241 DTC under the ABS section. This DTC doesn't light any lights. All you get is stiffer steering to let you know there is no steering assist.
First thing to check if you have that code is to make sure the 2 wire connector/harness coming from the EBCM is plugged into the rack.
I am attaching two diagnostics for C1241 one is for 2000 and older C5s and the other is for 2001 and newer C5s. Since there weren't really any changes in magnasteer through the C5 run it might make it easier for a DIYer to have two ways to look at things. The only major change was the EBCM changeover in 2001 which is why I provided before and after change over diagnostics.
Bill
Here is a description of how it operates:
Variable Effort Steering System Description and Operation
Description
The variable assist magnetic steering system MAGNASTEER® varies the driver effort required to steer the vehicle as speed changes. At low speeds, the system requires minimum steering effort for easy turning and parking maneuvers. Steering effort is increased at higher speeds in order to provide the driver with firmer steering (road feel) and directional stability. The EBCM controls a bi-directional magnetic rotary solenoid. The solenoid is located in the steering gear. The EBCM varies the steering assist by adjusting the current flow through the solenoid. The solenoid adjusts the amount of power steering assist in order to achieve a given level of driver effort to turn the vehicle.
MAGNASTEER® accomplishes this by adding or subtracting torque on the rotary input shaft to the power rack and pinion. The amount of steering assist is dependent upon vehicle speed. As the vehicle speed increases, the following actions occur:
• The steering assist decreases.
• The driver effort increases.
As the vehicle speed decreases, the following actions occur:
• The steering assist increases.
• The driver effort decreases.
Operation
The variable effort steering (VES) system uses inputs from the ABS wheel speed sensors and steering wheel position sensor to the EBCM to determine the desired amount of power steering assist.
The power steering pump magnetic rotary actuator regulates power steering fluid flow. The EBCM can change the amount of current flowing through the actuator.
The EBCM has the ability to detect malfunctions in the steering wheel position sensor, the actuator or the circuitry to those components. Any malfunction detected will cause the power steering assist to remain at maximum with the pintle in its normally retracted position for all speeds.
When the system is operating normally, increasing the vehicle speed will decrease power steering assist, allowing the driver to have improved road feel and directional stability. When the EBCM steering wheel position sensor detects sudden steering maneuvers, the EBCM reduces the actuator current in order to provide maximum steering assist.
Circuit Operation
When the Electronic Brake Control Module (EBCM) commands the Magnasteer Actuator ON, B+ is supplied through the EBCM to the MAGNASTEER actuator . Ground/control for the MAGNASTEER actuator is provided through the EBCM to MAGNASTEER actuator controls the amount of current supplied to the MAGNASTEER actuator based on the input from the wheel speed sensors.
VES Actuator
At the heart of the system is an electromagnetic actuator, which consists of a multiple-pole ring-style permanent magnet (that is attached to, and rotates with, the spool shaft or the input side of the system), a pole piece (that is attached to, and rotates with, the pinion or the output side of the system), and an electromagnetic coil assembly.
When the electronic controller senses the vehicle's speed, it generates an electrical current that is most appropriate for each speed. This current then energizes the electromagnetic coil, which causes the permanent magnet to seek alignment in relationship to the pole piece. (Note: Field strength increases with a higher current to increase the relative force between the permanent magnet and the pole piece.) Again, depending on the polarity of the current in the coil, the system, the current immediately ramps to 0 amps to provide a mid-range effort level. (Note: Currently, the principal input into the controller is vehicle speed. Other inputs may be added, such as steering wheel position, to derive lateral acceleration).
Use the DIC controls on the right side of the instrument panel to open the On Board Diagnostics and see if you have a C1241 DTC under the ABS section. This DTC doesn't light any lights. All you get is stiffer steering to let you know there is no steering assist.
First thing to check if you have that code is to make sure the 2 wire connector/harness coming from the EBCM is plugged into the rack.
I am attaching two diagnostics for C1241 one is for 2000 and older C5s and the other is for 2001 and newer C5s. Since there weren't really any changes in magnasteer through the C5 run it might make it easier for a DIYer to have two ways to look at things. The only major change was the EBCM changeover in 2001 which is why I provided before and after change over diagnostics.
Bill
