Aspen 4WD V8-5.7L Hybrid (2009)
Power Steering Pump: Description and Operation
Power Steering Pump - Operation
EPS System Operation
EPS SYSTEM OPERATION
The Electric Power Steering (EPS) Pump has different modes on which it will operate. A list of the modes follows:
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Wake Up Mode - The EPS Pump control module initiates when ignition is in RUN or START positions. This begins start-up checks (memory
checksums, internal sensors, faults etc.) and starts monitoring the vehicle CAN system.
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Start Mode - The EPS module will start the electric pump motor to provide steering assist once one of the following occurs: Hybrid propulsion
system active message is received (vehicle is started), or a vehicle speed message of greater than 3 mph (5 kp/h) is received.
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The EPS Pump will then run until the ignition is turned off regardless of further changes in Hybrid Propulsion System or Vehicle Speed messages.
There may be degraded assist during evasive maneuvers when there is no vehicle speed message.
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Sleep Mode - If steering wheel is not moved for 5 seconds with vehicle speed less than 3 mph (5 kp/h) the pump will reduce output flow to 0.5 gm
to minimize current consumption and heat buildup. Any steering wheel movement will return pump to normal operation.
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End-lock Mode - If the steering wheel is held in lock (wheels to wheel stops) for 1 second or more with vehicle speed less than 12.5 mph (20
kp/h) the pump will reduce output flow to 0.5gmm to minimize current consumption and heat buildup. NOTE: Holding the steering wheel in the
lock position for more than 3 seconds can damage the EPS system.
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Shut Down Mode - At shutdown (loss of ignition signal to the module), the pump will:
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Write any stored DTCs to EEPROM.
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Shut down.
Electric Power Steering (EPS) Pump
ELECTRIC POWER STEERING (EPS) PUMP
NOTE: If BOTH the Hybrid Propulsion System Active message (vehicle started) and Vehicle Speed Messages are missing at start-up, the EPS
pump will remain in Wake Up Mode and will not operate.
The EPS pump will start to provide steering assist when one of the following occurs:
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A Hybrid Propulsion System Active message (vehicle started) is received.
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A vehicle speed message of greater than 5 kp/h (3 mph) is received.
After the pump starts:
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If the Hybrid Propulsion System message is lost - the EPS pump will continue to run normally but will set a U0148 - Lost Communication with
Hybrid Gateway Module DTC.
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If the Vehicle Speed message is lost - the EPS pump will use a default vehicle speed of 85 kp/h (59 mph) to calculate desired flow and as a result,
steering effort will no longer be speed sensitive. The EPS Module will set a U0121 Lost Communication with ABS DTC.
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If the Steering Wheel Position message is lost - the EPS pump will use a default steering wheel rate of 230 deg/s to calculate desired flow and as a
result, steering effort may be higher on evasive steering maneuvers. The EPS Module will set a U0126 - Lost Communication with Steering Angle
Sensor DTC.
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If the pump internal temperature exceeds 110° Celsius (230° F) the pump will begin to reduce output to self protect.
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If the pump internal temperature exceeds 125° Celsius (257° F) internal temperature, the pump will shut off in order to self protect. The module
will set a C1592 - Electronic Power Steering Motor Circuit DTC.
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If the supply voltage drops below 9V or is above 16V, the EPS pump will shutoff to self protect. The EPS Module will set a C1588/C1589 -
Power Steering Motor Inverter Power Supply High/Low DTC.
The EPS pump will resume normal operation automatically once any missing message or out of range condition noted above is restored to normal.
