GM Service Manual Online
For 1990-2009 cars only

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.

Step

Action

Values

Yes

No

Schematic Reference: Antilock Brake System Schematics

1

Did you perform the ABS Diagnostic System Check?

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Go to Step 2

Go to Diagnostic System Check - ABS

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Select the display DTCs function on the scan tool for the powertrain control module (PCM).

Does the scan tool display DTC P1575?

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Go to DTC P1575 in Cruise Control

Go to Step 3

3

  1. With a scan tool, observe the Extended Travel Brake Switch parameter in the Delco/Bosch ABS/TCS ICCS data list.
  2. Step on and off the brake pedal with enough force to simulate a hard braking condition. As the brake pedal is pressed and released, the scan tool should read Applied and Released.
  3. Use a tape measure in order to measure the distance that the brake pedal travels for the scan tool to read Applied.

Does the distance measure within the specified range?

2.5-3.3 cm (1.0-1.3 in)

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

Go to Step 4

4

Adjust or repair the extended travel brake switch as necessary. Refer to Stop Lamp Switch Replacement in Hydraulic Brakes.

Did you complete the repair?

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Go to Step 5

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5

Operate the system in order to verify the repair.

Did you correct the condition?

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System OK

Go to Step 2