For 1990-2009 cars

### 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 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 will attempt to correct the vehicle yaw motion by applying differential braking to the left or right front wheel.

### Test Description

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

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

2. Verify that the Lateral Accelerometer Input parameter is within the valid range.

3. Verify that the Yaw Rate Input parameter is within the valid range.

Step | Action | Value(s) | 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
2 |

1. Install a scan tool.
2. Start the engine.
3. Observe the VSES is Centered parameter in the VSES data list.
4. Perform the Diagnostic Test Drive. Refer to Diagnostic Test Drive .

Did the scan tool display Yes within the specified value?

30 seconds

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3 | With the scan tool, perform the Steering Position Sensor Test. Did the steering wheel position sensor (SWPS) pass the test? | -- | Go to Step 4 | Go to Step 7
4 | 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 5 | Go to Step 8
5 | 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 6 | Go to Step 8
6 | Replace the electronic brake control module (EBCM). Refer to Control Module References for replacement, setup and programming. Did you complete the replacement? | -- | Go to Step 9 | --
7 | Replace the SWPS. Did you complete the replacement? | -- | Go to Step 9 | --
8 | Replace the yaw rate sensor/lateral accelerometer. Refer to Vehicle Yaw Sensor with Vehicle Lateral Accelerometer Replacement . Did you complete the replacement? | -- | Go to Step 9 | --
9 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | Go to Step 2