Circuit Description
The vehicle stability enhancement system (VSES) is activated by the electronic brake control module (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 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.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC C1281 VSES Sensors Uncorrelated |
| • | DTC C1283 Excessive Time to Center Steering |
| • | DTC C1286 Steering Sensor Bias Malfunction |
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 gram. |
| • | The yaw rate error is less than 5.8 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 is accomplished.
Action Taken When the DTC Sets
| • | The EBCM disables the VSES for the duration of the ignition cycle. |
| • | The driver information center (DIC) displays the Service Stability System message. |
| • | The ABS/traction control system (TCS) remains functional. |
Conditions for Clearing the DTC
| • | The condition for the DTC is no longer present and the DTC is cleared with a scan tool. |
| • | The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles. |
Diagnostic Aids
The following conditions can cause this concern:
| • | An improper steering alignment |
| • | An open, short to ground, or short to voltage |
| • | An internal lateral accelerometer failure |
| • | An EBCM internal failure |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step performs the Steering Position Sensor Test in order to verify that the steering wheel position sensor (SWPS) is operating properly.
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This step verifies that the lateral accelerometer input parameter is within the valid range.
-
This step verifies 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 Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
Did the steering wheel position sensor (SWPS) pass the test? | -- | Go to Step 3 | Go to Step 7 | |
With a scan tool, observe the Lateral Accelerometer Input parameter in the VSES 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 a scan tool, observe the Yaw Rate Sensor Input parameter in the VSES 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 electronic brake control module (EBCM). Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 10 | -- |
7 | Replace the SWPS. Refer to Steering Wheel Position Sensor Replacement 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 |
