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 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 1 analog input and 2 digital inputs, Phase A and Phase B, to the EBCM. By interpreting the relationship between the 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 DTC
C1281
| • | The steer angle has been centered. |
| • | The VSES is active. |
| • | The direction (understeer or oversteer) of the yaw rate error has not changed. |
| • | The centered lateral acceleration value is less than 0.5 g. |
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 the yaw rate error always in either understeer or oversteer. 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 steer rate less than 10 degrees/second, the difference between the analog steer angle and digital steer angle is greater than 20 degrees for 1 second. Under this condition, this DTC will set along with DTC C1287. |
C1283
The vehicle has driven for 10 minutes without completing steer angle centering.
C1286
The steering sensor bias moves greater than 20 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 50 consecutive drive cycles. |
Diagnostic Aids
The following conditions can cause this concern:
| • | Improper steering alignment. |
| • | Open, short to ground, or short to voltage. |
| • | Internal lateral accelerometer failure. |
| • | EBCM internal failure. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
Perform the Steering Position Sensor Test in order to verify that the steering wheel position sensor (SWPS) is operating properly.
-
Verify that the lateral accelerometer input parameter is within the valid range.
-
Verify that the yaw rate input parameter is within the valid range.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Antilock Brake System Schematics | ||||
1 | Did you perform the ABS Diagnostic System Check? | -- | Go to Step 2 | |
Did the steering wheel position sensor (SWPS) pass the test? | -- | Go to Step 3 | Go to Step 7 | |
With the scan tool, observe the Lateral Accelerometer Input parameter in the Delco/Bosch ABS/TCS ICCS2 data list. Does the scan tool display within the specified range? | 2.3-2.7 V | Go to Step 4 | Go to Step 8 | |
With the scan tool, observe the Yaw Rate Sensor Input parameter in the Delco/Bosch ABS/TCS ICCS2 data list. Does the scan tool display within the specified range? | 2.3-2.7 V | Go to Step 5 | Go to Step 9 | |
5 |
Does the DTC reset? | -- | Go to Step 6 | Go to Diagnostic Aids |
6 | Replace the EBCM. Refer to Electronic Brake Control Module Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- |
7 | Replace the steering wheel position sensor (SWPS). Refer to Steering Shaft, Lower Bearing, and Jacket - Disassemble - Off Vehicle and Steering Shaft, Lower Bearing, and Jacket - Assemble - Off Vehicle in Steering Wheel and Column. Did you complete the replacement? | -- | Go to Step 10 | -- |
8 | Replace the lateral accelerometer sensor. Refer to Lateral Accelerometer Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- |
9 | Replace the yaw rate sensor. Refer to Vehicle Yaw Sensor Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- |
10 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
