Electric Power Steering (EPS) has replaced hydraulic power steering in many new vehicles today. One of the advantages of electric power steering is that it eliminates the power steering pump, which can use as much as 8 to 10 horsepower under load. This improves fuel economy while also eliminating the weight and bulk of the power steering pump and hoses. Getting rid of the hydraulics also does away with fluid leaks and the need to check the power steering fluid. Electric power steering is also quieter than hydraulic systems because there is no pump noise and no fluid flowing through hoses and valves. But the most noticeable difference is in handling and steering refinement.
Electric power steering can be fine tuned with a precision that is hard to match with hydraulic controls. By monitoring the driver's steering inputs, vehicle speed, and other suspension dynamics, the system can provide just the right amount of steering feel and effort to match rapidly changing driving conditions. EPS can deliver extra effort when you need it, and reduce steering effort when you do not need it. It can even provide steering assist when the engine is off.
Better yet, because the system is software driven, it is possible to tap into the steering module and modify steering effort and feel. This can be done with a factory scan tool on some applications, and with aftermarket "tuner" scan tools and software.
ELECTRIC POWER STEERING APPLICATIONS
Electric power steering can be found on a wide variety of vehicles including the Acura NSX (which was the first production car with this feature), Honda S2000, Toyota Cortolla, Prius and Toyota RAV4, numerous GM models including 2004 and up Chevrolet Malibu, Chevrolet Cobalt , Equinox, HHR, Pontiac G6 (except the Convertible, GTP and 2007 GT models), Pontiac G5, Torrent and Vibe, Saturn ION and VUE, 2005 and up Ford Mustang, and many many others.
HOW ELECTRIC POWER STEERING WORKS
Though some of the older electric power steering systems were actually "electro-hydraulic," and used an electric motor to drive a conventional hydraulic pump, the latest generation of EPS is all electric/electronic. The steering gear itself is a manual rack with an electric motor mounted on the steering column or the rack.
When the driver turns the wheel, a steering sensor detects the position and rate of rotation of the steering wheel. This information along with input from a steering torque sensor mounted in the steering shaft is fed to the power steering control module. Other inputs such as vehicle speed and inputs from the traction control or stability control systems are factored in to determine how much steering assist is required. The control module then commands the motor to rotate a certain amount, and a sensor on the motor provides feedback to the control module so it can monitor the motor's position.
Toyota Prius electrtic steering system
CHEVY COBALT ELECTRIC POWER STEERING MODES
The General Motors EPS system has several modes of operation:
* Normal mode -- Left and right assist is provided in response to inputs and vehicle speed.
* Return mode -- Used to assist steering return after completing a turn. Feedback from the steering position sensor prevents the EPS system from "overshooting" the center position.
* Damper control mode -- Used to improve road feel and dampen kickback. This mode typically kicks in at higher vehicle speeds.
* Protection mode -- Protects electrical components from thermal damage and excessive current flow if the steering is held all the way to one side in the lock position too long.
Turning the steering wheel all the way to one side will cause the Power Steering Control Module (PSCM) to command the maximum amount of current to the EPS motor. If the steering wheel is then held in this position for an extended period of time, the system will go into protection mode so the motor doesn't overheat. In this mode, the PSCM will limit the amount of current to the motor and reduce the level of power assist.
If the PSCM detects a high system temperature and the overload protection mode is enabled, a DTC C0176 "System Thermal Error" code may be set. On some models, DTC C0476 "Electric Steering Motor Circuit Range/Performance" may also be set. These DTCs indicate normal PSCM action (reduced steering assist) to prevent thermal damage to power steering system components. Consequently, there is nothing that needs to be fixed. But the driver needs to be educated about not cranking and holding the steering against either stop for a prolonged period of time.
If a sensor or other component in the EPS system fails, the self-diagnostics should detect the fault, set a code and disable power-assist. A warning light will illuminate to alert the driver, and the driver will notice a significant increase in steering effort when turning the vehicle. The vehicle will still be safe to drive, but it will require more steering effort to do so.
REPLACEMENT PARTS FOR ELECTRIC POWER STEERING
On the GM EPS applications, the electric motor is mounted on the steering column. The motor and PSCM module are both part of the steering column assembly, and are currently replaced as a unit if there is a problem with the system. On some other applications (Toyota, for example), the electric motor can be replaced separately.
Electric steering assist motors can either be located at the base of the steering column, as with GM, or integral with the steering rack, as with Honda. The GM type uses a separately serviced motor assembly, while the Honda type requires rack replacement if the motor is defective.
Electric power steering columns can be expensive to replace, costing anywhere from $600 to $1500 or more depending on the application. So accurate diagnosis is essential to avoid replacing parts unnecessarily.
After a PSCM or steering column replacement, it may be necessary to use a scan tool needs to calibrate the center position of the steering wheel position sensor, select the "steering tuning" for the vehicle, or calibrate the center position of the steering shaft torque sensor.
AFTERMARKET ELECTRIC POWER STEERING UNITS
For customizers and street rod builders, Flaming River now sells an aftermarket electric power steering that can be adapted top fit various vehicles. But it is a very expensive item, costing $4000 to $6000 depending on the version. The benefits of using an electronic power steering unit in these kind of applications is that it simplifies installation and eliminates the need for a power steering pump and hoses.
ELECTRIC POWER STEERING DIAGNOSTIC TIPS
The steering wheel position sensor determines the "on center" position. This is used to keep return assist from going over center once a turn is completed. The GM unit is 5 volt dual analog triangle signal device with a valid signal voltage range of 0 to 5 volts. The sensors signal 1 and signal 2 voltage values will increase and decrease within 2.5 to 2.8 volts of each other as the steering wheel is turned. This information can be very useful during diagnosis.
In GM EPS systems, the Power Steering Control Module (PSCM) must be set up with the correct "steering tuning", which are different in relation to the vehicles Powertrain configuration, sedan, coupe, tire and wheel size, etc.
GM has a technical service bulletin (07-02-35-004 Feb. 02, 2007) out on a noise problem with EPS steering on the Cobalt, Chevy HHR and Pontiac G5. The bulletin describes a steering column rattle or knocking noise that may be heard or felt at low speeds (5 to 15 mph). The noise is most noticeable when making a slow turn on a loose or rough surface. The EPS system can be temporarily disabled by removing the 60 amp EPS fuse in the under-hood fuse block. If the rattle persists, it is due to backlash within the steering column (assist motor gear mechanism). Replace the 60 amp EPS fuse and test drive again. If the steering column is identified as the source of the rattle/knocking noise, the steering column needs to be replaced.
March 2, 2010
GM issues Recall on Vehicles with Electric Power Steering
General Motors is recalling 1.3 million 2005 to 2010 Chevrolet Cobalts, 2007 to 2010 Pontiac G5s, 2005 to 2006 Pontiac Pursuits sold in Canada, and 2005 to 2006 Pontiac G4s sold in Mexico to fix power steering motors that might fail.
GM says these cars are still safe to drive, but warns that a power steering motor failure can increase steering effort significantly, especially at speeds under 15 mph. If the electric power steering motor fails, you may see a warning light come on and hear a chime, or you may not. Eitehr way, brace yourself because the steering will suddenly feel much stiffer require much mor effort to turn the car.
GM says it will replace the electric motors on all 1.3 million vehicles, but that it will take some time to get the new power steering motors from their supplier, JTEKT Corp.. GM says it will notify car owners when the parts are available for installation.
The recall is in response to an investigation launched by the National Highway Traffic Safety Administration in response to over 1,100 complaints it has received about cars losing their power steering assist. The complaints included 14 crashes and one injury.
GM says it will fix the older models first because it typically takes about 20,000 to 30,000 miles of driving for the condition to develop. If the power steering assist fails, it usually comes back for a time after the car is shut off and restarted. But the problem won't go away. Fixing it requires replacing the electric motor that provides the power assist.
March 31, 2014
GM Issues Another Electronic Steering Recall
GM has recalled 1.5 million cars for a possible defect in the electric motor that provides power assisted steering on the vehicles below. If the motor fails, the vehicle reverts to manual steering and may be difficult to steer. GM says it will replace the electric motor at no cost to the vehicle owner.
GM Sticky Steering Problem Recall
GM has issued a recall notice #14232A covering the following vehicles with Electronic Power Steering:
2012-2014 Buick Verano
GM says that the above vehicles equipped with electronic power steering (NJ0/NJ1, may have increased friction in the steering system. This could cause the steering wheel to stick in the straight-ahead position after driving long distances on a straight highway. The steering wheel can be turned but it may require increased effort.
GM says it is extending the warranty on the steering systems on these vehicles to 10 years or 150,000 miles (240,000 km), whichever occurs first, from the date the vehicle was originally placed in service, regardless of ownership.
Dealers are to replace the steering gear on 2010-2012 model year vehicles, or reprogram the power steering control module on 2013-2014 model year vehicles. The repairs will be made at no charge to the customer.
GM Recalls over a Million Chevy and GMC Trucks for Electronic Power Steering Defect
GM issued a recall for over 1 million full-size pickups and large SUVs due to a software defect with the electronic steering system that can cause a temporary loss of steering at low speed. GM said it had identified 30 crashes, two injuries but no deaths linked to the defect.
Vehicles covered by the recall include 2015 Chevrolet Silverado 1500 and GMC 1500 pickups, GMC Yukon, 2015 Chevy Tahoe and Suburban, and 2015 Cadillac Escalade SUVs.
The GM recall number is 18289, and the NHTSA recall number is 18V586000.
The NHTSA safety report 18V-586 describes the problem as follows:
Description of the Cause :
Events that demand high current, such as low speed turns, can cause emporary low voltage conditions. When the system voltage drops below 8.8 volts for more than 1 second—e.g., during low-speed turns—EPS assist is disabled until voltage returns to 9 volts for a minimum of 40 milliseconds, at which point EPS assist returns.
Description of the Safety Risk :
If EPS assist is lost and suddenly returned, the driver could have difficulty steering the vehicle, especially at low speeds, increasing the risk of a crash.
Identification of Any Warning that can Occur :
If power steering assist is lost (i.e., the vehicle reverts to manual steer) a driver information center (DIC) message may alert the driver to an EPS problem. Also, other electrical sub-systems may shut down at the same time or just before the event, which could temporarily disable the radio, Stabilitrack, the DIC, chimes, door-lock cycling, air conditioning, or cruise.
Owners of the recalled vehicles are being notified by GM. Free repairs include reflashing the steering control module with updated software.
This is not the first recall for an electronic steering problem on these vehicles. In 2014, there was a recall of 679 vehicles (NHTSA #14V719000) for a defective electric power steering control module. The fix was to replace the orginal module with a new one.
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