Specifications

Chassis Specialist : Electric Power Steering
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One common customer complaint on both systems is a no steering assist concern. This usually happens
in a parking lot manoeuvre or when a vehicle is being used for driver instruction. If the steering wheel
is held on the steering stop, the PSCM will command maximum current to the motor. If the steering
wheel is held in this position for several seconds, the PSCM will limit the current to the EPS to protect
against excessive heat. The driver will be able to detect the loss of assist and usually the driver
information centre will display No Steering Assist and the service steering system light will illuminate.
The PSCM will set a DTC C0176, system thermal error or a C0476, electric power steering motor
circuit range/performance. If a vehicle has either of these trouble codes set in history, ask the customer
about the operating conditions when the fault occurred. If the steering system is relaxed for a couple of
minutes the power assist will return after the PSCM has determined the EPS motor has cooled
sufficiently.
Saturn Astra Electro-Hydraulic Power Steering
Beginning with the 2008 model year Saturn introduced the Astra. This compact vehicle uses an electric
hydraulic power steering (EHPS) system. The Astra uses one of two different versions of the EHPS
system depending on the options it is built with. One is manufactured by TRW and is used on vehicles
with the base engine and suspension. The other system is built by ZF and is used on vehicles with the
larger engine and up-level suspension system.
The system consists of a steering column with an integrated torque sensor, a PSCM and an electric
hydraulic power steering pump. The steering column and torque sensor are serviced as an assembly
while the PSCM, hydraulic motor and steering gear are serviced individually. On models with either
the ZF or stability control they will also have a column integration module (CIM) which incorporates a
steering angle sensor.
The steering column motor and torque and/or position sensors operate the same as on the other GM
vehicles. This system differs by using hydraulic pressure supplied by an electric pump. The PSCM uses
information from the CAN network regarding vehicle speed and from the torque sensor to determine
the correct steering assist. The PSCM then communicates this calculation to the control unit of the
hydraulic pump. The control unit controls the pump speed and hydraulic pressure. The pump and
control unit are serviced as an assembly. Due to the power required to run the motor and pump, the
engine must be running for the system to operate.
The TRW and ZF components cannot be interchanged.
As the system uses pressurized hydraulic fluid, the level must be checked at regular service intervals.
To check the fluid level, remove the cap located on the right side of the engine compartment. It is
located between the engine and the front bulkhead. Verify the level reads correctly on the dipstick. If