GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The vehicle stability enhancement system (VSES) is activated by the electronic brake control mdoule (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 drivers 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.

Conditions for Running the DTC

The EBCM performs 6 different tests to detect a DTC condition. The numbers below correspond to the numbers in Conditions for Setting the DTC.

  1. The yaw rate sensor bias test runs with the ignition ON.
  2. The yaw rate sensor acceleration test runs with the ignition ON.
  3. The yaw rate sensor circuit test runs with the vehicle stopped or with the vehicle speed greater than 45 km/h (28 mph).
  4. The yaw rate isolation test runs with the following conditions:
  5. • The brake pedal is not pressed.
    • The ABS is not active.
    • The vehicle speed is greater than 5 km/h (3 mph).
  6. The above yaw rate isolation test run with the VSES active.
  7. The false activation test runs with the VSES active.

Conditions for Setting the DTC

The EBCM performs 6 different tests to detect a DTC condition. The numbers below correspond to the numbers in Conditions for Running the DTC.

  1. The yaw rate bias is greater than 7 degrees/second.
  2. The yaw rate input change is greater than 390 degrees/second/second.
  3. The yaw rate input voltage is less than 0.15 volts or greater than 4.85 volts for 1 second.
  4. The yaw rate error is greater than 10 degrees/second 30 times within a drive cycle.
  5. The yaw rate error is greater than 10 degrees/second for 5 seconds. Under this condition, this DTC will set along with DTC C1281.
  6. 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 C1281.

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 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:

    • 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.

  1. Tests for the proper operation of the circuit in the low voltage range.

  2. Tests for the proper operation of the circuit in the high voltage range. If the fuse in the jumper opens when you perform this test, the signal circuit is shorted to ground.

  3. Tests for a short to voltage in the 5-volt reference circuit.

  4. Tests the bias voltage of the yaw rate sensor.

Step

Action

Values

Yes

No

Schematic Reference: Antilock Brake System Schematics

Connector End View Reference: Antilock Brake System Connector End Views

1

Did you perform the ABS Diagnostic System Check?

--

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. With a scan tool, observe the Yaw Rate Sensor Input parameter in the VSES data list.

Does the scan tool display that the Yaw Rate Sensor Input parameter is within the specified range?

0.15-4.85 V

Go to Step 6

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the yaw rate sensor connector.
  3. Turn ON the ignition, with the engine OFF.
  4. With the scan tool, observe the Yaw Rate Sensor Input parameter.

Does the scan tool display that the Yaw Rate Sensor Input parameter is less than the specified value?

0.15 V

Go to Step 4

Go to Step 10

4

  1. Turn OFF the ignition.
  2. Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the yaw rate sensor and the signal circuit of the yaw rate sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. With the scan tool, observe the Yaw Rate Sensor Input parameter.

Does the scan tool display that the Yaw Rate Sensor Input parameter is greater than the specified value?

4.85 V

Go to Step 5

Go to Step 8

5

  1. Disconnect the fused jumper wire.
  2. Measure the voltage between the 5-volt reference circuit of the yaw rate sensor and the low reference circuit of the yaw rate sensor.

Does the voltage measure within the specified range?

4.85-5.2 V

Go to Step 12

Go to Step 7

6

Does the scan tool display that the Yaw Rate Sensor Input parameter is within the specified range?

2.3-2.7 V

Go to Diagnostic Aids

Go to Step 11

7

Test the 5-volt reference circuit of the yaw rate sensor for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 13

8

Test the 5-volt reference circuit of the yaw rate sensor for the following conditions:

    • An open
    • A short to ground
    • A high resistance

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 9

9

Test the signal circuit of the yaw rate sensor for the following conditions:

    • An open
    • A short to ground
    • A high resistance

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 13

10

Test the signal circuit of the yaw rate sensor for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 13

11

  1. Disconnect the EBCM harness connector.
  2. Install the J 39700 universal pinout box using the J 39700-300 cable adapter to the EBCM harness connector only.
  3. Test the low reference circuit of the yaw rate sensor for a high resistance or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 12

12

Inspect for poor connections at the harness connector of the yaw rate sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 14

13

Inspect for poor connections at the harness connector of the EBCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 16

Go to Step 15

14

Replace the yaw rate sensor. Refer to Vehicle Yaw Sensor Replacement .

Did you complete the repair?

--

Go to Step 16

--

15

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

Did you complete the repair?

--

Go to Step 16

--

16

  1. Clear the DTCs using the scan tool.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK