C1286

DTC C1281, C1283, Or C1286:

DTC C1281, C1283, or C1286

Circuit Description
The vehicle stability enhancement system (VSES) adds an additional level of vehicle control to the EBCM.

Yaw rate is the rate of rotation about the vehicle's vertical axis. The VSES is activated when the EBCM determines that the desired yaw rate does not match the actual yaw rate as measured by the yaw rate sensor.

The desired yaw rate is calculated from the following parameters:
^ The position of the steering wheel
^ The speed of the vehicle
^ The lateral, or sideways, acceleration of the vehicle

The difference between the desired yaw rate and the 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 attempts to correct the vehicle's yaw motion by applying differential braking to the appropriate wheel. The amount of differential braking applied is based on both the yaw rate error and side slip rate error.

The VSES activations generally occur during aggressive driving, in turns or on bumpy roads without much use of the accelerator pedal. When braking during VSES activation, the pedal pulsations feel different than the ABS pedal pulsations. 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 two analog inputs to the EBCM. The two input signals are approximately 90 degrees out of phase. By interpreting the relationship between the two 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 faster than 10 km/h (6 mph) for more than 10 seconds in a straight line on a level surface.

Conditions for Running the DTC C1281
^ The steer angle has been centered.
^ The VSES is active.
^ The direction (understeer or oversteer) of the delta velocity error has not changed.
^ The centered lateral acceleration value is less than 0.5 g.
^ The yaw rate error is less than 6 degrees/second.
^ The side slip error is greater than 1.8 meters/second*second.

C1283
The vehicle speed is greater than 40 km/h (25 mph).

C1286
The steer angle has been centered.

Conditions for Setting the DTC C1281
One of the following conditions exists:
^ The VSES is engaged for 10 seconds with a constant understeer or oversteer condition. Under this condition, this DTC will set by itself.
^ The yaw rate error is greater than 10 degrees/second for 5 seconds. Under this condition, this DTC will set along with DTC C1282.
^ The yaw rate error is greater than 10 degrees/second with the vehicle speed less than 60 km/h (37 mph) and the acceleration pedal is pressed more than 25 percent of the pedal travel range for 1 second during the VSES activation. Under this condition, this DTC will set along with DTC C1282.
^ With the yaw rate less than 8 degrees/second, the side slip error is greater than 4.9 meters/second2 for 5 seconds. Under this condition, this DTC will set along with DTC C1284.
^ With the steer rate less than 80 degrees/second, the difference between the 2 steering sensor signals (Phase A and Phase B) is greater than 20 degrees for 1 second. Under this condition, this DTC will set along with DTC C1287.

C1283
The vehicle has been driven for 10 minutes without completing steer angle centering.

C1286
The steering sensor bias moves more than 40 degrees after steer centering was accomplished.

Action Taken When the DTC Sets
^ The EBCM disables the VSES for the duration of the ignition cycle.
^ The DIC displays the Service Stability System message.
^ The ABS/TCS remains functional.

Conditions for Clearing the DTC
^ The condition for the DTC is no longer present (the DTC is not current) and you used the scan tool Clear DTC function.
^ The condition for the DTC is no longer present (the DTC 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
^ 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 DTC was set (when the DIC displayed the Service Stability System 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 that the steering wheel position sensor (SWPS) is operating properly.
3. Verify that the lateral accelerometer input parameter is within the valid range.
4. Verify that the yaw rate input parameter is within the valid range.