GM Service Manual Online
For 1990-2009 cars only

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 yaw motion by applying differential braking to the left or right front wheel.

Test Description

The number below refers to the step number 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.

Step

Action

Values

Yes

No

Schematic Reference: Antilock Brake System Schematics

1

Did you perform the ABS Diagnostic System Check?

--

Go to Step 2

Go to Diagnostic System Check - ABS

2

Inspect the mounting of the yaw rate sensor. Refer to Vehicle Yaw Sensor Replacement .

Did you find and correct the condition?

--

Go to Step 15

Go to Step 3

3

  1. Install a scan tool.
  2. Start the engine.
  3. With a scan tool, observe the Yaw Rate Sensor Input parameter in the VSES data list.
  4. Perform the Diagnostic Test Drive. Refer to Diagnostic Test Drive .

Does the scan tool display suddenly increase or decrease without rapid turning of the vehicle?

--

Go to Step 4

Go to Step 5

4

Perform the diagnosis for DTC C1282. Refer to DTC C1282 .

Did you find and correct the condition?

--

Go to Step 15

Go to Step 12

5

  1. Straighten the front wheels.
  2. Observe the Dual Analog SWPS Input A and Dual Analog SWPS Input B in the VSES data list.
  3. Slowly rotate the steering wheel in both directions.

Does the scan tool display change states as the steering wheel was rotated?

--

Go to Step 6

Go to Step 14

6

With the scan tool, perform the Steering Position Sensor Test.

Did the SWPS pass the test?

--

Go to Step 7

Go to Step 14

7

  1. Place the vehicle on a level surface.
  2. 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 9

Go to Step 8

8

Inspect the mounting of the lateral accelerometer sensor. Refer to Lateral Accelerometer Replacement .

Did you find and correct the condition?

--

Go to Step 15

Go to Step 9

9

Inspect the EBCM for the proper part number.

Did you find the correct part number?

--

Go to Step 10

Go to Step 12

10

Inspect the power steering gear for the proper part number.

Did you find the correct part number?

--

Go to Step 11

Go to Step 13

11

Inspect the alignment of the vehicle. Refer to Wheel Alignment Measurement in Wheel Alignment.

Did you find and correct the condition?

--

Go to Step 15

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

12

Important: Perform the setup procedure for the EBCM. An unprogrammed EBCM will result in the following conditions:

   • Inoperative or poorly functioning system operations
   • The EBCM sets DTC C1248 and DTC C1255m3

Replace the EBCM. Refer to Electronic Brake Control Module Replacement .

Did you complete the repair?

--

Go to Step 15

--

13

Replace the power steering gear. Refer to Steering Gear Replacement in Power Steering System.

Did you complete the repair?

--

Go to Step 15

--

14

Replace the steering wheel position sensor (SWPS). Refer to Steering Wheel Position Sensor or Steering Shaft Lower Bearing Replacement in Steering Wheel and Column.

Did you complete the repair?

--

Go to Step 15

--

15

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2