DESCRIPTION AND OPERATION > STEERING SYSTEM > ELECTRONIC POWER ASSIST STEERING (EPAS) SYSTEM

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Clement Houston
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1 2010 Ford Fusion 2.5L Eng SEL Service Manual: STEERING SYSTEM - ELECTRONIC POWER ASSIST STEERING (EPAS) DESCRIPTION AND OPERATION > STEERING SYSTEM > ELECTRONIC POWER ASSIST STEERING (EPAS) SYSTEM The Electronic Power Assist Steering (EPAS) system consists of the following components: Power Steering Control Module (PSCM) - the PSCM controls the functions of the EPAS system and communicates with other modules that are on the High Speed Controller Area Network (HS-CAN) bus. The PSCM is attached to the RH side of the EPAS gear assembly and is not available separately for service. Motor - the EPAS gear uses a 12-volt reversible motor to control the steering effort. The motor is connected to the steering rack by a toothed belt and a pulley/bearing assembly. The motor is used by the PSCM to move the rack inside the gear housing. Motor position is used to determine steering wheel angle/position instead of using a separate sensor. The motor is attached to the RH side of the EPAS gear assembly and is not available separately for service. Steering shaft torque sensor - the steering shaft torque sensor is used by the PSCM to determine how much force the steering wheel is being turned. The sensor sends out 2 signals, one for left and one for right. When the steering wheel is turned to the left, the left signal increases while the right signal decreases, likewise when the steering wheel is turned to the right, the right signal increases while the left signal decreases. This allows the PSCM to determine if the driver intends to go left or right in order to spin the motor in the appropriate direction. The sensor is mounted near the input shaft of the EPAS gear assembly and is not available separately for service. Inner tie rod - one inner tie rod is located at each end of the EPAS gear assembly and is available separately for service. Refer to POWER STEERING. Outer tie rod - one outer tie rod is located at each end of the EPAS gear assembly and is available separately for service. Refer to POWER STEERING. EPAS gear bellows boot - one bellows boot is located on each side of the EPAS gear assembly. Each boot is held in place with 2 boot clamps. The boots and clamps are available for service, refer to POWER STEERING. EPAS gear isolators - there are several rubber isolators (one at each attaching point) on the EPAS gear assembly. These isolators aid in reducing NVH concerns and not available separately for service. The EPAS system utilizes a rack-and-pinion type steering gear. Power assist is provided by a motor that is connected to the steering rack by a belt and a pulley and bearing assembly. The steering gear and motor/module are serviced as an assembly. A new steering gear includes inner tie rods, however, the inner and outer tie rods can also be serviced separately. For information on tie-rod end service, refer to POWER STEERING. DIAGNOSIS AND TESTING > STEERING SYSTEM > PRINCIPLES OF OPERATION > ELECTRONIC POWER ASSIST STEERING (EPAS) SYSTEM The Electronic Power Assist Steering (EPAS) system provides power steering assist to the driver by replacing the conventional hydraulic valve system with an electric motor coupled to the steering rack by a toothed belt. The motor is controlled by the Power Steering Control Module (PSCM) that senses steering effort/use through the use of a torque sensor which is mounted near the input shaft of the steering gear. Steering assist is provided in proportion to the steering input effort and vehicle speed. The EPAS system requires a 12-volt, hot at all times feed for system operation. The PSCM is

2 activated when power is applied to the hard-wired ignition/run input. After activation, the PSCM monitors the High Speed Controller Area Network (HS-CAN) bus to determine if the vehicle is operating in a manner capable of supporting the EPAS system. Once this is determined, vehicle speed sent by the PCM over the HS-CAN bus, steering shaft speed and direction sent by the torque sensor and steering wheel angle/position determined by the motor position all provide the necessary information for the PSCM to determine the amount or level of assist provided by the EPAS system. Assist is primarily based off of vehicle speed. As vehicle speed increases, the amount of assist provided by the system is decreased to improve and enhance road feel at the steering wheel. As vehicle speed decreases, the amount of assist provided by the system is increased to ease vehicle maneuvering. If the vehicle speed is missing or out of range, the PSCM defaults to a safe level of assist for all driving conditions. If the vehicle speed returns to the correct in-range values, the PSCM will adjust the level of assist accordingly. Steering wheel/shaft torque, speed and direction information will allow the PSCM to determine how much assist is needed to turn the wheels right and left. The PSCM is self-monitoring and has the capability of setting and storing DTCs. Depending on the DTC set, the control module will enter into a "safe mode" of manual steering. In addition, the PSCM may send a request to the Instrument Panel Cluster (IPC) module over the HS-CAN bus to display a message in the message center to alert the driver of a potential EPAS concern. INTERACTIVE DIAGNOSTICS > DTC / SYMPTOM SELECTION > SYMPTOM CHART - STEERING SYSTEM AND NVH > STEERING SYSTEM AND NVH NOTE: NVH symptoms should be identified using the diagnostic tools that are available. For a list of these tools, an explanation of their uses and a glossary of common terms, refer to NOISE, VIBRATION & HARSHNESS. Since it is possible any one of multiple systems may be the cause of a symptom, it may be necessary to use a process of elimination type diagnostic approach to pinpoint the responsible system. If this is not the causal system for the symptom, refer back to NOISE, VIBRATION & HARSHNESS for the next likely system and continue diagnostics. Select a symptom to see recommended actions Message center displays POWER STEERING ASSIST FAULT NOTE: This message will appear when a condition has been detected in the electronic power assist steering (EPAS) system that requires the power steering control module (PSCM) to disable the system (remove assist) to help prevent the system from sustaining any possible damage. This message (and related symptom) may be cleared when the ignition key is cycled and may not be present at the time of diagnostics. DTCs present in the PSCM GO to PINPOINT TEST KC Message center displays SERVICE POWER STEERING NOTE: This message will appear if a condition exists (high friction for example)

3 that puts extra load on the EPAS gear. Steering assist will remain for the current ignition cycle. If the ignition is turned OFF and then back ON, SERVICE POWER STEERING NOW will appear on the message center and steering assist will be removed until the condition that caused the message to appear is repaired. DTCs present in the PSCM GO to PINPOINT TEST KC Message center displays SERVICE POWER STEERING NOW NOTE: This message will appear when a condition has been detected in the EPAS system that requires the PSCM to disable the system (remove assist) to help prevent the system from sustaining any possible damage. This message (and related symptom) will not clear until the condition that caused the message to appear has been repaired. DTCs present in the PSCM GO to PINPOINT TEST KC Excessive steering wheel play. Excessive steering wheel play is a condition in which there is too much steering wheel movement before the wheels move. A small amount of steering wheel free play is considered normal. Steering column shaft/u-joints Steering linkage GO to PINPOINT TEST G Steering gear internal failure. Lack of assist or inconsistent assist NOTE: If the steering wheel is held at the end of travel for more than 2 seconds, the electronic power assist steering (EPAS) gear will noticeably reduce assist. This is a normal condition programmed into the power steering control module (PSCM) to protect the system from permanent damage. NOTE: There are multiple conditions (overheating protection, high voltage, low voltage, etc.) that will result in limited or reduced assist from the EPAS system. Address all existing PSCM DTCs prior to diagnosing any assist symptoms.

4 Lack of assist or inconsistent assist is experienced when the steering wheel effort is higher than normal. Hard steering can remain constant through the full turn or occur near the end of a turn. It is important to know the difference between hard steering/lack of assist and poor returnability/sticky steering. If equipped, active park assist can only be activated if the steering system is providing full steering assist. If the active park assist system is currently in use and the steering system experiences a partial or non-assist event, active park assist will be deactivated. Fuse(s) Wiring, terminals or connectors. Suspension components Steering gear internal failure. GO to PINPOINT TEST I Inner tie rods Outer tie rods No communication with the PSCM. Fuse(s) Wiring, terminals or connectors. High-speed communication area network (HS-CAN) bus REFER to COMMUNICATIONS NETWORK to diagnose the no communication concern. Steering gear Poor returnability/sticky steering Poor returnability and sticky steering is used to describe the poor return of the steering wheel to center after a turn or steering correction is completed. Binding lower steering column shaft coupling/u-joint Loose, worn or damaged steering linkage Binding suspension components Binding steering gear GO to PINPOINT TEST I Binding steering gear bearing(s) Binding steering column shaft dash panel

5 seal Alignment/suspension Steering system pull/drift/wander NOTE: The EPAS system is designed to compensate for some steering issues (drift, pull, wander, etc.). If the steering issue is severe enough the steering wheel may become off center due to system compensation. Drift describes what a vehicle with this condition does with the hands off the steering wheel. A vehicle-related drift/pull, on a flat road, can cause a consistent deviation from the straight-ahead path and require constant steering input in the opposite direction to counteract the effect. Drift/pull can be induced by conditions external to the vehicle, such as wind or road camber. Pull is described as a tugging sensation on the steering wheel felt by the driver, which must be overcome to keep the vehicle going straight. Wander is the tendency of the vehicle to require frequent, random left and right steering wheel corrections to maintain a straight path down a level road. Alignment Tire(s) Suspension components Steering column shaft/u-joints GO to PINPOINT TEST H Steering column Steering gear mounts Steering gear Feedback (rattle, chuckle or knocking noise) - roughness is felt in the steering wheel when driven over rough surfaces Steering column shaft/coupling bolts are loose. TIGHTEN the bolts to specification. REFER to SPECIFICATIONS. Steering column shaft/coupling joints damaged or worn. INSTALL a new steering column shaft. REFER to STEERING COLUMN.

6 Grinding noise or gravely feel Damaged steering gear bellows boots GO to PINPOINT TEST K Shimmy lose, damaged or worn tie-rod ends GO to PINPOINT TEST J Steering column squeaks, clicks or grinds. Loose or misaligned steering column shrouds. TIGHTEN the steering column shroud screws. Steering wheel rubbing against steering column shrouds. ALIGN the steering column shrouds. Steering gear clunk occurs only while cornering over a bump (can be temperature sensitive). NOTE: Some noise when turning into the steering stops is normal. Steering gear insulators or mounting bolts loose or damaged TIGHTEN the bolts to specification or INSTALL new bolts as necessary. Steering gear has reached the end of travel and is contacting the steering stops. COMPARE to other EPAS vehicles. If the noise is excessive, INSPECT the outer tie-rods and suspension ball joints. TIGHTEN or INSTALL new as necessary. Steering wheel is off center. NOTE: The EPAS system is designed to compensate for some steering issues (drift, pull, wander, etc.). If the steering issue is severe enough the steering wheel may become off center due to system compensation.

7 Alignment Steering gear GO to PINPOINT TEST H Whirring or whine noise that gets louder with increased steering wheel speed. NOTE: Some amount of noise from the EPAS gear is considered normal. Grounded or loose steering column shaft dash panel seal. REPAIR or INSTALL a new dash panel seal as necessary. REFER to Steering Column Shaft in STEERING COLUMN. COMPARE to other EPAS equipped vehicles. If the noise is excessive, INSTALL a new EPAS gear. Steering gear REFER to STEERING GEAR L FRONT WHEEL DRIVE (FWD), STEERING GEAR L ALL WHEEL DRIVE (AWD) or STEERING GEAR L NON-HYBRID AND 3.0L FRONT WHEEL DRIVE (FWD). INTERACTIVE DIAGNOSTICS > PINPOINT TESTS > PINPOINT TEST I - POOR RETURNABILITY/STICKY STEERING AND LACK OF ASSIST OR INCONSISTENT ASSIST > NORMAL OPERATION With a fully charged battery and the ignition ON, the electronic power assist steering (EPAS) system should provide adequate assist to maneuver the vehicle and should be able to return to the straight-ahead position with little difficulty. The assist provided by the EPAS system should be smooth and consistent at all times. The steering and suspension components should be free of any binding conditions and should not interfere with the steering assist provided by the EPAS system. If the steering wheel is held at lock end for more than 2 seconds the EPAS system will reduce assist noticeably. This is a normal condition programmed into the power steering control module (PSCM) to protect the system from permanent damage. I1: CHECK CHARGING SYSTEM VOLTAGE Start the vehicle. Make sure the engine ready indicator is illuminated for hybrid vehicles, with the vehicle running, turn the steering wheel from lock to lock and take the voltage measurement while holding the wheel in a lock position. Measure the voltage between:

8 (+)12 Volt Vehicle Battery (-)12 Volt Vehicle Battery Positive terminal Negative terminal Turn the steering wheel from lock to lock with the vehicle running and note the PID reading while holding the wheel in a lock position. Access the PSCM and monitor the MOD_SUP_V (VOLT) PID. Is the battery voltage greater than 13 volts and does the PID match battery voltage +/- 1.5 volts? Yes No Go to I2. Go to A4. I2: CHECK THE EPAS GEAR Isolate the EPAS gear and linkage, and check for any binding conditions. Are the gear and linkage free from any binding conditions? Yes Go to I3. No ISOLATE the component(s) causing the binding. INSTALL new component(s) as necessary.refer to POWER STEERING SYSTEM.DRIVE the vehicle to VERIFY the repair. I3: CHECK THE STEERING COLUMN SHAFT AND DASH SEAL Isolate the steering column shaft and dash seal, and check for any binding conditions. Are the shaft and seal free from any binding conditions? Yes No The condition may be caused by tires, wheel knuckles and/or ball joints.refer to DIAGNOSIS AND TESTING. ISOLATE the component(s) causing the binding. INSTALL new component(s) as necessary.refer to Steering Column Shaft in REMOVAL AND INSTALLATION.DRIVE the vehicle to VERIFY the repair.

ELECTRONIC POWER ASSIST STEERING (EPAS) SYSTEM

2013 Ford Truck Explorer 2WD V6-3.5L Vehicle > Steering and Suspension > Steering > Description and Operation > Components ELECTRONIC POWER ASSIST STEERING (EPAS) SYSTEM Electronic Power Assist Steering