The DTC description in the GM Shop Manual is:

OTC C1287 or C1288
Circuit Description
The vehicle stability enhancement system (VSES) is
activated by the EBCM calculating the desired yaw rate and comparing it to the actual yaw rate input. The
desired yaw rate is calculated from measured steering wheel position, vehicle speed, and lateral acceleration. The difference between the desired yaw rate and actual yaw rate is the yaw rate error, which is a measurement of oversteer or understeer. If the yaw rate error
becomes too large, the EBCM will attempt to correct the vehicle's yaw motion by applying differential braking to the left or right front wheel.
The amount of differential braking applied to the left or right front wheel is based on both the yaw rate error and side slip rate error. The side slip rate error is
a function of the lateral acceleration minus the product of the yaw rate and vehicle speed. The yaw rate
error and side slip rate error are combined to produce the total delta velocity error. When the delta velocity
error becomes too large and the VSES system
activates, the driver's steering inputs combined with
the differential braking will attempt to bring the
delta velocity error toward zero.
The VSES activations generally occur during
aggressive driving, in the turns or bumpy roads without much use of the accelerator pedal. When braking
during VSES activation, the brake pedal will feel
different than the ABS pedal pulsation. The brake pedal pulsates at a higher frequency during VSES activation.
The usable output voltage range for the lateral
accelerometer and yaw rate sensors is 0.25-4. 75 volts. The scan tool will report zero lateral acceleration or
yaw rate as 2.5 volts with no sensor bias present.
The sensor bias compensates for sensor mounting
alignment errors, electronic signal errors, temperature changes, and manufacturing differences.
The steering wheel position sensor supplies 2 analog
inputs, Phase A and Phase B, to the EBCM. The 2 input signals are approximately 90 degrees out of phase.
By interpreting the relationship between the 2 inputs,
the EBCM can determine the position of the steering
wheel and the direction of steering wheel rotation.
Steer angle centering is the process by which the
EBCM calibrates the steering sensor output so that the output reads zero when the steering wheel is
centered. Using the yaw rate input, lateral
accelerometer input, and wheel speed sensor inputs, the initial steering center position is calculated
after driving greater than 10 km/h (6 mph) for more
than 10 seconds in a straight line on a level surface.

Conditions for Running the OTC

The ignition is ON.

Conditions for Setting the OTC

C1288
One of the following conditions exists:

• Both Phase A and Phase B are greater than
4.9 volts for 1.6 seconds.
• Both Phase A and Phase B are less than 0.2 volls for 1.6 seconds.
• The difference in the changes in Phase A and
Phase B is greater than 35.2 degrees for
9.76 milliseconds.

Action Taken When the DTC Sets:

• The EBCM disables the VSES for the duration of the ignition cycle.
• The Traction Control and Active Handling indicate­ turns ON.
• The DIC displays the Service Active Handling
message.
• The ABS/TCS remains functional.

Conditions for Clearing the OTC:

• The condition for the OTC is no longer present (the OTC is not current) and you used the
scan tool Clear DTC function.
• The condition for the DTC is no longer present (the OTC is not current) and you used the
On-Board Diagnostics Clear DTC function.
• The EBCM automatically clears the history DTC when a current DTC is not detected in
100 consecutive drive cycles.

Diagnostic Aids:

• The scan tool may display 2 additional characters after the DTC. Take note of the 2 character code and any other DTCs that are set. The 2 character code is an engineering aid used in order to determine the specific criteria which caused the DTC to set.
• During diagnosis, park the vehicle on a level surface.
• Check the vehicle for proper alignment. The car should not pull in either direction while driving straight on a level surface.
• Find out from the driver under what conditions the ore was set (when the DIC displayed the Service Active Handling message). This information will help to duplicate the failure.
• The Snapshot function on the scan tool can help find an intermittent DTC.

Test Description
The numbers below refer to the step numbers on the diagnostic table.

2. Perform the Steering Position Sensor Test in order to verify if the steering wheel position sensor (SWPS) is operating properly.

3. Tests for the proper operation of the steering wheel position signal A circuit in the low
voltage range.
4. Tests for the proper operation of the steering wheel position signal B circuit in the low
voltage range.
5. Tests for the proper operation of the steering wheel position signal A circuit in the high voltage range. If the fuse in the jumper opens when
you perform this test, the signal circuit is shorted to ground.
6. Tests for the proper operation of the steering wheel position signal B circuit in the high voltage range. If the fuse in the jumper opens when
you perform this test, the signal circuit is shorted to ground.
7. Tests for a short to voltage in the 5 volt reference circuit.
8. Tests for a high resistance or an open in the low reference circuit.

As you can see I need to perform a Steering Position Sensor Test. which I cannot locate on my scan tool

Tags: PRO