I got an email from someone who reads the forums but doesn't actually post on them. He asked me to put this information up as it might be of use to the readers. I can't take credit or accept responsibility for the accuracy of this information etc but it's worth a read.
Ian said:CORSA ELECTRIC POWER STEERING
There are some common faults with the Corsa Electric Power Steering
that manifest themselves as one or both of these conditions
1: The car pulls to one side or is easier to turn in one direction when
all else seems to be correct. E.g. Tyres equal, steering and
suspension geometry good, brakes and wheel bearings good, driven on
a straight and level road.
2: When turning, the steering will randomly seem to jam or stick for
an instant and the steering wheel becomes suddenly heavy, and then
reverts to normal.
Both of these can be rectified using a few commonly available tools
and less than an hour's work. By many accounts the solution from your
friendly Vauxhall Opel dealer is to replace the entire column.
FAULT DESCRIPTION
The most common problem by far with the Corsa EPS is caused by the
torque sensing mechanical components wearing with age leading to an
error with the torque sensor reading that gradually gets worse. The
the situation can be rectified by adjusting the position of the torque
sensor to a new zero position.
1: Steering pulls or has a preference for one direction
========================================================
Full details of this procedure are available with photographs
elsewhere, but it is worthwhile mentioning now that you will need a
a good degree of dexterity and a few useful tools to achieve it. Tools:
Medium-sized Phillips screwdriver, T2.5 Torx bit, flexible driver,
small 2BA or 1/4" ring spanner, 13mm ring spanner.
Method:
Turn the Steering wheel to expose the two pop-on screw covers on the
retaining screws for the steering column switch covers, removing the
covers and the two Phillips screws underneath. Remove the three
Phillips screws underneath the lower steering column switch cover and
remove the cover. Remove the fuse cover and take out the two screws
beneath the fuse box to allow the lower section of the dash to be
pulled away.
On the lower right-hand side of the steering column assembly just
inside the dash, there are two Torx screws holding the steel cover
the plate that protects the torque sensor. Remove both of these using the
flexible driver and T2.5 Torx bit. Remove the cover. Before
proceeding, mark the position of the sensor body relative to the steering
column body.
If you only need to reset the torque sensor position, you need only
loosen the screws to allow adjustment. If you need to fix the
sticking steering problem then the sensor must be removed. The torque
the sensor is retained with two more T2.5 Torx screws. The lower
retaining screw can be accessed fairly easily by pulling the lower
the right section of the dash away from the metal structure. The upper
one is more difficult and maybe slackened using the Torx bit in a
small ring spanner.
Next, turn the steering column to gain access to the bolt that
secures the lower steering column universal joint to the rack spigot
that projects up through the floor. Remove the retaining bolt and
swivel the joint away.
If you have a short piece of plastic drain pipe or a cardboard tube,
slide it over the universal joints so that the steering column is
free to turn without jamming on anything (like your hands).
BEFORE TURNING ON THE IGNITION, READ ALL OF THIS BIT!.
When the ignition is turned on and the engine started, the EPS will
drive the steering column depending on the reading of the torque sensor.
If you do this now, there is a chance that the wheel will be driven
continuously in one direction. The column has a position sensor at the
top behind the steering wheel that will count 30 turns from end to
end before it jams. Check this before proceeding. Then turn the wheel
back to centre (15 turns from one extreme).
Now be ready to turn off the ignition if the next step causes the
wheel to spin rapidly. Turn on the ignition and start the engine. The
steering may spin rapidly, Switch off if it does. Rotate the torque
sensor fractionally and turn on the engine again. Repeat this process
until the steering is still when the engine is running.
Then, give the steering wheel a short tug in one direction and let it
settle, then do the same in the other direction. The wheel may
continue a little or might bounce back a little. If necessary adjust
the torque sensor position until the behaviour is identical in both
directions.
Now switch off, and check the steering centre position by counting
the turns, and reset it in the central position.
Repeat the torque sensor setting procedure to ensure that the
behaviour is identical in both directions. Adjust if necessary. When
you are satisfied that the steering is balanced and neutral turn off
the ignition, and tighten the sensor retaining screws.
Refit the Sensor cover, re-assemble the lower universal joint, refit
the covers and screws and test drive.
2: Random Jamming or "notchy" steering.
========================================
This fault is caused by the mechanical components that translate the
steering column effort (Control Demand) into motion that is
proportional to torque. Direction is inferred by the magnitude of the
torque being positive or negative. This mechanical translation is
managed using a slant-pivot coupling connecting the upper and lower
parts of the steering column that operates a sliding collar normally
held in a central position by springs. The motion of the slant-pivot
coupling is limited, and at either extreme allows direct coupling
between the upper and lower sections of the steering column. The
a torque sensor detects the position of the sliding collar and produces
an electrical signal to represent the effort and direction of turning
the steering wheel. The EPS system then activates the motor that
drives the lower section of the steering column in the correct
direction to reduce the sensor reading to zero. i.e. No more turning
is demanded.
The problem occurs when the slant-pivot coupling or the sliding
collar bind or lock at some position in the travel. The components
are lubricated when built, but the lubricant degrades over time and
eventually hardens and dries where it is thinnest. When the steering
is turned slowly or by a small amount the friction at some points is
enough to make the coupling bind rather than slide, causing a zero
torque reading that effectively removes all power assistance until
the coupling moves. To the driver, this seems like the steering just
got very heavy or jammed for an instant.
It is possible to reinvigorate the assembly using a mixture of
ordinary gear oil and a molybdenum disulfide based additive such as
molyslip or stop smoke.
Method:
Carry out the same procedure as case 1, then mark the correct
position of the torque sensor and remove it.
Inject no more than 15cc of the Oil & MoS2 lubricant mixture into the
void around the sliding collar and replace the torque sensor
carefully. It will be necessary to rotate the sensor until the sensor
actuator engages with the sliding collar correctly. Until the sensor
is correctly engaged it will fail to seat properly. Do not force it
into place or use the screws to try and pull it into position. The
The sensor arm is biased to one end by a spring and it will have moved
when the sensor was extracted. Offer it into place and feel for the
a situation where the sensor arm spring tension can be detected. When
it is in the right position it will just go into place easily and
then it can be rotated to the correct neutral position as previously
marked.
Before replacing everything else, start the engine and check that the
steering behaves properly. If it turns in one direction switch off
immediately and reset the torque sensor position by following the
procedure for case 1.
After lubricating the internal components, a few days may need to
elapse before the lubricant penetrates all parts of the coupling.
Over this time the steering will gradually become lighter and may
start to favour one direction as the coupling finds a new equilibrium
position. If this occurs it will be necessary to reset the torque
sensor position again.
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