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.

C1284

The EBCM performs 7 different tests to detect a DTC condition. The numbers below correspond to the numbers in Conditions for Setting the DTC.

1. The lateral accelerometer sensor bias test runs with the ignition ON.
2. The lateral accelerometer sensor self test runs with the following conditions:

•	The ignition is ON.

•	The vehicle is stopped.

3. The lateral accelerometer sensor jerk test runs with the ignition ON.
4. The centered lateral accelerometer sensor test runs with the following conditions:

•	The ignition is ON.

•	The vehicle is stopped.

5. The lateral accelerometer sensor isolation test runs with the following conditions:

•	The ignition is ON.

•	DTC C1282 is not set.

•	The yaw rate is less than 8 degrees/second.

6. The above lateral accelerometer sensor isolation test runs with the VSES active.
7. The yaw rate sensor and lateral accelerometer sensor uncorrelated test with the following conditions:

•	The vehicle speed is greater than 10 km/h (6.2 mph) and less than 100 km/h (62 mph).

•	The centered yaw rate has a value that is positive and is greater than 10 degrees/second

C1285

The ignition is ON.

C1284

The EBCM performs 7 different tests to detect a DTC condition. The numbers below correspond to the numbers in Conditions for Running the DTC.

1. The compensated bias value of the lateral accelerometer sensor is greater than 0.3 g.
2. The lateral accelerometer sensor performs a self test that results in an offset of 0.5 g. The EBCM compares the sensor output during the self test with the output following the test. The DTC sets when the lateral acceleration immediately following the self test is greater than the self test output minus 0.4 g.
3. The lateral jerk is greater than 16.5 g/second for 0.12 seconds more than 2 times within the ignition cycle.
4. The lateral acceleration is 0.4 g for 0.25 seconds.
5. The side slip error is greater than 0.5 g 30 times within a drive cycle.
6. The side slip error is greater than 0.5 g for 5 seconds. Under this condition, this DTC will set along with DTC C1281.
7. The oversteer term is negative for 2 seconds. The oversteer term is the yaw rate value times the lateral acceleration value. Under this condition, this DTC will set along with DTC C1281.

C1285

The lateral accelerometer input voltage is less than 0.15 volts or greater than 4.85 volts for 1 second.

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

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

4. 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.

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

6. Tests the bias voltage of the lateral accelerometer sensor.