Circuit Operation
The variable effort steering (VES) system uses the EBCM data in order
to determine the desired amount of power steering assist. The EBCM receives
signals from the following components:
| • | The ABS wheel speed sensors |
| • | The steering wheel speed sensor |
The power steering pump actuator has a pintle that moves in and out
of an orifice. The pintle regulates the power steering fluid pressure. The
EBCM changes the amount of current flowing through the EVO actuator. If the
power steering pump actuator is disconnected, the pintle is pushed out of
the orifice for maximum power steering assist.
The EBCM detects malfunctions in the following components:
| • | The steering wheel speed sensor |
| • | The power steering pump actuator |
| • | The circuitry to the EVO solenoid and the steering wheel position
sensor |
When a malfunction is detected, the following conditions exist:
| • | The power steering assist is at the maximum level. |
| • | The pintle remains in a retracted position for all speeds. |
When the system operates normally, an increase in vehicle speed decreases
power steering assist. The decrease in power assist gives the driver improved
road feel and directional stability. Sudden steering wheel turns, such as
evasive maneuvers, are detected by the EBCM through the steering wheel speed
sensor. The EBCM then reduces current to the solenoid actuator. The reduced
current allows greater power steering assist.
Variable Effort Steering (VES)
Diagnostic trouble codes (DTCs) are stored in the EBCM for power steering
pump actuator and steering wheel speed sensor malfunctions.
Enhanced Diagnostics
Enhanced diagnostic information, found in the DTC HISTORY function of
the scan tool, is designed to provide the service technician with specific
malfunction information. The DTC HISTORY function stores the following information:
| • | The first 5 diagnostic trouble codes (DTCs). |
| • | Data to identify the specific DTC. |
| • | The number of occurrences. |
| • | The order of occurrence. |
| | The order of occurrence is useful in order to determine if a previous
malfunction is linked to the most recent malfunction. For example, when an
intermittent steering wheel speed sensor circuit becomes completely
open. |
| • | The number of drive cycles since the malfunction first occurred. |
| | A drive cycle occurs under the following conditions: |
| • | The ignition is turned to RUN. |
| • | The vehicle is driven faster than 16 km/h [10 mph]. |
| • | A malfunction is present and signals the drive cycle counter by
turning the ignition to RUN and OFF. |
| • | The number of drive cycles since the malfunction last occurred. |
During difficult diagnosis situations, gather more information in order
to identify the trends in malfunction occurrences. Begin by asking the following
questions:
| • | Did the malfunction only occur once over a large number of drive
cycles, indicating an unusual condition was present when the malfunction occurred? |
| | A malfunction that only occurs once in 50 drive cycles may have
been caused by a severe vehicle impact or unusual vehicle suspension movement,
such as driving at high speed over a large pothole or a speed bump. Malfunction
resolution is unlikely. |
| • | Does the malfunction occur infrequently over a large number of
drive cycles, indicating that special diagnostic techniques may be required
in order to identify the source of the malfunction? |
| | A malfunction that occurs infrequently, such as 3 out of 15 drive
cycles, may be caused by severe weather changes, or other external environmental
conditions. |
| | If the malfunction has not recurred for a long period of time, seek
customer information regarding recent vehicle repairs. If no repair was made,
use diagnostics techniques in order to locate difficult-to-recreate problems.
Refer to Electrical Diagnosis or Diagnostic Aids for the DTC in question. |
| • | Does the malfunction occur intermittently? |
| | An intermittent malfunction is difficult or impossible to duplicate.
Refer to Diagnostic Aids. |
