C1285
DTC C1284 or C1285
Steps 1 - 4
Steps 5 - 13
Steps 14 - 16
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 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 driver's 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.
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 2 analog inputs, Phase A and Phase B. to the EBCM. The 2 input signals are approximately 90 degrees out of phase. By interpreting the relationship between the 2 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.
Conditions for Running the DTC
C1284
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 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.
C1285
The ignition is ON.
Conditions for Setting the DTC
C1284
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 compensated bias value of the lateral accelerometer sensor is greater than 0.39.
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 0.8 g.
3. The lateral jerk is greater than 19 g/second for 0.01 seconds.
4. The lateral acceleration is 0.4 g for 0.25 seconds.
5. The side slip error is greater than 4.9 meters/second/second 30 times within a drive cycle.
6. The side slip error is greater than 4.9 meters/second/second for 5 seconds. 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.
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 (the DTC is not current) and you used the scan tool Clear DTC function.
^ The condition for the DTC is no longer present (the DTC is not current) and you used the On-Board Diagnostics Clear DTC function.
^ The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.
Diagnostic Aids
^ During diagnosis, park the vehicle on a level surface.
^ Check the vehicle for proper alignment. The car should not pull in either direction while driving straight on a level surface.
^ Find out from the driver under what conditions the DTC was set (when the DIC displayed the Service Stability System message). This information will help to duplicate the failure.
^ The Snapshot function on the scan tool can help find an intermittent DTC.
Test Description
The number below refers to the step number 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.