Specifications

Chassis Specialist : Electric Power Steering
Page 14
High
Speed
GMLAN
Serial Data
Bus
RUN/START
BODY
CONTROL
MODULE
(BCM)
FUSE
BLOCK-
UNDERHOOD
POWER
DISTRIBUTION
SCHEMATICS IN
WIRING SYSTEMS
POWER
DISTRIBUTION
SCHEMATICS IN
WIRING SYSTEMS
STEERING
COLUMN
ASSEMBLY
EPS
FUSE
60A
DLC Schematics
in Computer/Integrating
Systems
Battery
Positive
Voltage
Ignition 1 Voltage
ELECTRIC POWER
STEERING
(EPS)
MOTOR
STEERING SHAFT
TORQUE SENSOR
RIGHT
ASSIST
MOTOR
CONTROL
LEFT ASSIST
MOTOR CONTROL
LOGIC
GROUND
POWER
DISTRIBUTION
SCHEMATICS IN
WIRING SYSTEMS
POWER
STEERING
CONTROL
MODULE
(PCSM)
High
Speed
GMLAN
Serial Data
Bus+
High
Speed
GMLAN
Serial Data
Bus-
EPS
STR WHL
CNTRL
Fuse 19
2A
60A
COBALT EPS WIRING SCHEMATIC
High
Speed
GMLAN
Serial Data
Bus+
The Saturn Astra uses an electro hydraulic system. The system consists of a PSCM, steering column
with an integral torque sensor, EPS motor and steering gear. The system is different than the other two
systems as the EPS motor is used to increase hydraulic pressure to assist the steering system. The
PSCM will PWM the current to the EPS motor based on vehicle speed, torque sensor input and vehicle
suspension options. If the vehicle is equipped with a stability system then a steering wheel position
sensor will be added to the column. The Astra uses two different EPS systems; one is built by TRW
and communicates on a dedicated diagnostic line (pin 7 on the DLC). The other system is built by ZF
and communicates on the high speed GM LAN. The TRW system can be identified by a round fluid
reservoir, the EPS wiring harness cannot be disconnected at the motor and the hydraulic lines are
individually connected to the motor unit.
Diagnostic trouble codes can be accessed using a scan tool. The list below is a typical list of EPS
trouble codes.