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'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 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.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | DTC C1284 Lateral Accelerometer Sensor Bias Malfunction |
| • | DTC C1285 Lateral Accelerometer Sensor Circuit Malfunction |
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.
- The lateral accelerometer sensor bias test runs with the ignition ON.
- The lateral accelerometer sensor self test runs with the following conditions:
- The lateral accelerometer sensor jerk test runs with the ignition ON.
- The centered lateral accelerometer sensor test runs with the following conditions:
- The lateral accelerometer sensor isolation test runs with the following conditions:
- The above lateral accelerometer sensor isolation test run with the VSES active.
| • | The ignition is ON. |
| • | The vehicle is stopped. |
| • | The ignition is ON. |
| • | The vehicle is stopped. |
| • | The ignition is ON. |
| • | DTC C1282 is not set. |
| • | The yaw rate is less than 8 degrees/second. |
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.
- The compensated bias value of the lateral accelerometer sensor is greater than 0.3 grams.
- The lateral accelerometer sensor performs a self test that results in an offset of 0.5 grams. 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 grams.
- The lateral jerk is greater than 19 grams/second for 0.01 seconds.
- The lateral acceleration is 0.4 grams for 0.25 seconds.
- The side slip error is greater than 4.9 meters/second*second 30 times within a drive cycle.
- 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 driver information center (DIC) displays the Service Stability System message. |
| • | The ABS/traction control system (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:
| • | An improper steering alignment |
| • | An open, short to ground, or short to voltage |
| • | An internal lateral accelerometer failure |
| • | An EBCM internal failure |
Test Description
The number below refers to the step number on the diagnostic table.
-
This step tests for the proper operation of the circuit in the low voltage range.
-
This step 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.
-
This step tests for a short to voltage in the 5-volt reference circuit.
-
This step tests the bias voltage of the lateral accelerometer 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 Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | ||||||
2 |
Does the scan tool display that the Lateral Accelerometer Input parameter is within the specified range? | 0.15-4.85 V | Go to Step 6 | Go to Step 3 | ||||||
Does the scan tool display that the Lateral Accelerometer Input parameter is less than the specified value? | 0.15 V | Go to Step 4 | Go to Step 10 | |||||||
Does the scan tool display that the Lateral Accelerometer Input parameter is greater than the specified value? | 4.85 V | Go to Step 5 | Go to Step 8 | |||||||
Does the voltage measure less the specified value? | 5.1 V | Go to Step 12 | Go to Step 7 | |||||||
Does the scan tool display that the Lateral Accelerometer 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 lateral accelerometer 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 lateral accelerometer sensor for the following conditions:
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 lateral accelerometer sensor for the following conditions:
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 lateral accelerometer 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 |
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 lateral accelerometer 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 lateral accelerometer sensor. Refer to Lateral Accelerometer Replacement . Did you complete the replacement? | -- | Go to Step 16 | -- | ||||||
15 | Replace the EBCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 16 | -- | ||||||
16 |
Does the DTC reset? | -- | Go to Step 2 | System OK | ||||||
