Electronic Power Assist Steering: Other Ford Explorer V

Material(s)

MATERIAL(S)

Network Message Chart

MODULE NETWORK INPUT MESSAGES: PSCM

The PSCM controls the functions of the EPAS system and communicates with other modules over the HS-CAN .

To activate the EPAS system, a 12-volt hot at all times and a 12-volt ignition/run input to the PSCM is required. The PSCM then monitors the HS-CAN to determine if the vehicle is operating in a manner capable of supporting the EPAS system.

The PSCM uses inputs from various modules over the HS-CAN , the steering torque sensor and the motor to determine the amount or level of assist provided by the EPAS system.

The steering torque 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. 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 turn left or right in order to spin the motor in the appropriate direction.

The EPAS gear uses a 12-volt reversible motor to control the steering effort. The motor is connected to the rack of the steering gear by a toothed belt and pulley/bearing assembly. The motor is used by the PSCM to move the rack inside the steering gear housing. The position of the motor is used to determine steering wheel angle/position instead of using a separate sensor.

The PSCM continually monitors and adjusts steering efforts based on the torque sensor, motor position and HS-CAN inputs to enhance the feel of the steering system. The level of steering assist is primarily based on vehicle speed. As vehicle speed increases, the amount of assist decreases to improve and enhance road feel at the steering wheel. As vehicle speed decreases, the amount of assist increases to ease vehicle maneuvering. Compensation is made to reduce the effect of pull or drift that can be experienced when driving on roads with a high degree of camber.

The PSCM is self-monitoring and is capable of setting and storing DTCs . Depending on the DTC set, the PSCM may enter a failure mode. REFER to Failure Modes . In addition, the PSCM may send a request to the IPC over the HS-CAN to display a message in the message center, alerting the driver of a potential EPAS concern.

Failure Modes

When a DTC is present in the PSCM, the EPAS enters 1 of 2 modes of operation.

Reduced Steering Assist Mode

The EPAS enters a reduced steering assist mode to protect the internal components of the EPAS when a concern is detected by the PSCM, such as, low/high battery voltage or over-temperature concerns that are not considered to be a critical safety concern. The steering assistance sets to a default level and does not change with vehicle speed. This indicates that the steering assistance available for slow speed maneuvering is reduced, giving the steering a heavy feel. The assistance at high speed is greater than normal and can give the steering a lighter than normal feel.

Manual Steering Mode

The EPAS enters a manual steering mode (no electrical steering assistance is provided) when a concern that is considered to be a critical safety concern is detected or when a concern that caused the EPAS to enter reduced steering assist mode has been present for a predetermined number of key cycles. In manual steering mode, the vehicle has mechanical steering operation only, which gives steering operation a heavy feel.

Active Park Assist

Active park assist is an optional feature on this vehicle. REFER to PARKING AID SYSTEM - ACTIVE PARK ASSIST

Steering Gear

The EPAS gear is an assembly that consists of a PSCM, a motor, a steering shaft torque sensor and EPAS gear isolators, all of which are serviced as an assembly. The inner and outer tie rods and the gear bellows boots are available for service.

1. The steering shaft torque sensor is mounted near the input shaft of the EPAS gear and is used by the PSCM to determine how much force the steering wheel is being turned by.
2. The EPAS gear has one inner tie rod located at each end of the gear assembly and is available separately for service.
3. The EPAS gear has one outer tie rod located at each end of the gear assembly and is available separately for service.
4. The EPAS gear has one bellows boot located at 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.
5. The EPAS gear has isolators located at each attachment point of the gear. These isolators aid in the reduction of NVH concerns and are not available separately for service.

Power Steering Control Module (PSCM)

The PSCM is the ECU for the EPAS system. The module monitors all sensor inputs and HS-CAN messages that relate to the EPAS system and directly controls the output of the EPAS motor. If a new PSCM is installed, the module must be programmed with the correct vehicle information. REFER to PROGRAMMABLE MODULE INSTALLATION (PMI) .

When the active park assist system is enabled, the Parking Aid Module (PAM) will utilize ultrasonic sensors to locate and measure a parking space. Once a parking space is identified by the system and chosen by the driver, the PAM will then send steering command messages to the PSCM over the HS-CAN bus. The PSCM will utilize steering angle information transmitted by the Steering Angle Sensor Module (SASM) over the HS-CAN bus and wheel speed information transmitted by the ABS module over the HS-CAN bus to actuate the steering system as requested by the PAM.

Any driver inputs via the steering wheel will deactivate the active park assist system. Also, the presence of certain DTCs in the PSCM and/or ABS module will disable the system or keep the system from being activated. Refer to PARKING AID SYSTEM - ACTIVE PARK ASSIST for information on the active park assist system.

Known Concerns

1. KC1: KNOWN CONCERNS Ignition ON, engine OFF. NOTE: If present, diagnose DTC U3000:96 before diagnosing any other DTCs. Press Read Vehicle Information button to retrieve DTC s from the vehicle. NOTE: DTCs may be displayed from previous diagnostic actions. OASIS symptom code: -Stop/Steer/Ride \ Steering/Steering Wheel (662***) OASIS will return known TSBs and SSMs for the specific symptom code(s) and DTC(s) listed above. Are any of the listed known concerns related to the customer complaint? Yes No REPAIR as necessary. DTC Index

Possible Causes

1. Heavy loads on the EPAS gear.
2. Excessive ambient temperatures.

Action

DIAGNOSE any other PSCM DTC before diagnosing DTC B1D23:68. If no other DTC's are present, ADVISE the customer that high ambient temperatures and/or heavy loads on the EPAS system will cause this DTC to set, resulting in higher than usual steering effort. A heavy load is defined as multiple parking lot maneuvers over a short duration of time with low tire pressure or towing for long distances followed by multiple parking maneuvers.

1. Inner Tie Rods
2. Steering gear internal failure.

1. Steering gear internal failure.

1. Steering gear internal failure.

GO to PINPOINT TEST B

1. Steering gear internal failure.

INSTALL a new steering gear. REFER to Steering Gear .

1. Low tire air pressure.
2. Damaged steering gear bellows boot
3. Contaminated gear/rack.
4. Inner tie rods
5. Steering gear internal failure.

GO to PINPOINT TEST F

1. Fuse(s)
2. Wiring, terminals or connectors.
3. Other CAN bus modules

Refer to MODULE COMMUNICATIONS NETWORK to diagnose the high-speed controller area network (HS-CAN) bus.

1. Fuse(s)
2. Wiring, terminals or connectors.
3. PCM

CARRY OUT a self-test of the PCM. If the scan tool indicates that the module is not responding, REFER to MODULE COMMUNICATIONS NETWORK to diagnose the network communication concern. If PCM DTCs are present, REFER to the ENGINE CONTROLS - POWERTRAIN DTC CHARTS & DESCRIPTIONS (EXCEPT DIESEL & HYBRID) to diagnose the PCM.

1. Fuse(s)
2. Wiring, terminals or connectors.
3. DTCs present in the ABS module.

CARRY OUT an ABS module self-test. If the scan tool indicates the module is not responding, REFER to MODULE COMMUNICATIONS NETWORK to DIAGNOSE the network communication concern. If ABS module DTCs are present, REFER to ANTI-LOCK BRAKE SYSTEM AND STABILITY CONTROL to DIAGNOSE the ABS system fault.

1. Fuse(s)
2. Wiring, terminals or connectors.
3. DTCs present in the SCCM

CARRY OUT a self test on the SCCM. If the scan tool indicates that the module is not responding, REFER to MODULE COMMUNICATIONS NETWORK to diagnose the network communication concern. If DTCs are present in the SCCM, REFER to the DTC CHART: STEERING COLUMN CONTROL MODULE (SCCM) .

1. Fuse(s)
2. Wiring, terminals or connectors.
3. DTCs present in the RCM
4. RCM

CARRY OUT a self-test of the RCM. If the scan tool indicates the module is not responding, REFER to MODULE COMMUNICATIONS NETWORK to diagnose the network communication concern. If RCM DTCs are present, REFER to DTC CHART: RESTRAINT CONTROL MODULE (RCM) to diagnose the SRS fault.

1. Fuse(s)
2. Wiring, terminals or connectors.
3. DTCs present in the PAM
4. PAM

CLEAR the DTCs and CARRY OUT a self-test of the PSCM. If the DTCs return, CARRY OUT a self-test of the PAM. If the scan tool indicates that the PAM is not responding, REFER to MODULE COMMUNICATIONS NETWORK to diagnose the network communication concern. If DTCs are still present in the PAM, REFER to DTC CHART: PARKING AID MODULE (PAM) for diagnostic information.

1. Incomplete/incorrect PSCM flash update
2. Steering gear internal failure.

RE-FLASH the PSCM software. Clear the DTC and repeat the self-test. If the DTC returns, install a new EPAS gear referring to REMOVAL AND INSTALLATION .

1. DTCs present in the PCM
2. PCM HS-CAN bus concern

RETRIEVE and RECORD all PCM DTCs. REFER to the ENGINE CONTROLS - POWERTRAIN DTC CHARTS & DESCRIPTIONS (EXCEPT DIESEL & HYBRID) to diagnose the engine speed or vehicle speed concern.

1. DTCs present in the ABS module.
2. ABS module HS-CAN bus concern

1. DTCs present in the SCCM
2. SCCM HS-CAN bus concern

RETRIEVE and RECORD all SCCM DTCs. REFER to DTC CHART: STEERING COLUMN CONTROL MODULE (SCCM) to diagnose the SCCM.

1. DTCs present in the RCM
2. RCM HS-CAN bus concern

RETRIEVE and RECORD all RCM DTCs. REFER to DTC CHART: RESTRAINT CONTROL MODULE (RCM) to diagnose the lateral acceleration concern.

1. DTCs present in the PAM.
2. PAM HS-CAN concern.

RETRIEVE and RECORD all PAM DTCs. REFER to DTC CHART: PARKING AID MODULE (PAM) to diagnose the PAM.

1. Steering gear internal failure.

1. PSCM not configured.
2. PSCM configuration not complete.

CHECK the vehicle history for recent service actions related to this module. If there have been recent service actions with this module, REPEAT the PMI procedure as directed by the scan tool or CONFIGURE the PSCM using vehicle as-built data. If there have been no recent service actions, INSTALL a new EPAS gear to correct the failure to retain configuration data.

1. Heat shield missing.
2. Heavy loads on the EPAS gear.
3. Excessive ambient temperatures.
4. Ice/frost build up on relay contacts.
5. Incorrect EPAS gear installed.
6. Steering gear internal failure.

1. Fuse(s)
2. Wiring, terminals or connectors.
3. 12-volt battery
4. Charging system
5. PSCM

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

1. 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.

Message center displays SERVICE POWER STEERING

1. NOTE: This message will appear if a condition exists (high friction for example) 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.

Message center displays SERVICE POWER STEERING NOW

1. 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.

Excessive steering wheel play

1. 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.

Lack of assist or inconsistent assist

1. 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.
2. 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.
3. 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.
4. 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.

No communication with the PSCM

Poor returnability/sticky steering

1. 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.
2. NOTE: Before continuing with the diagnostic procedures, compare the vehicle steering feel/returnability with a like vehicle and confirm there is a concern present. NOTE: If the feel/returnability matches the comparison vehicle there is no fault. NOTE: If the feel/returnability does not match the comparison vehicle continue with the diagnosis.

Steering system pull/drift/wander

1. 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.
2. Drift describes what a vehicle with this condition does with the hands off the steering wheel.
3. 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.
4. Drift/pull can be induced by conditions external to the vehicle, such as wind or road camber.
5. 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.
6. 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.

Feedback (rattle, chuckle or knocking noise) - roughness is felt in the steering wheel when driven over rough surfaces

Grinding noise or gravely feel

Shimmy

Steering column squeaks, clicks or grinds.

Steering gear clunk occurs only while cornering over a bump (can be temperature sensitive).

Steering wheel is off center

Whirring or whine noise that gets louder with increased steering wheel speed.

1. NOTE: Some amount of noise from the EPAS gear is considered normal.

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