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.
Conditions for Running the DTC
C1284
The EBCM performs 2 different tests to detect a DTC condition. The number below corresponds to the number in Conditions for Setting the DTC.
- The lateral accelerometer self test is run at initialization. The output of the sensor will be offset by a large fixed amount for a short period of time after ignition power is first applied to the EBCM. The test will run under the following conditions:
- The lateral accelerometer bias test is run with the ignition ON.
| • | The ignition is ON. |
| • | All 4 wheel speeds are 0 km/h (0 mph). |
| • | The steer angle is within 90 degrees of centered. |
| • | The period of time between 0.23 seconds and 0.28 seconds after ignition power is first applied to the EBCM. |
C1285
The ignition is ON.
Conditions for Setting the DTC
C1284
The EBCM performs 2 different tests to detect a DTC condition. The numbers below correspond to the numbers in Conditions for Running the DTC.
- The lateral accelerometer signal does not increase by 0.4 g above the normal signal level.
- The compensated bias value of the lateral accelerometer is greater than 0.3 g.
C1285
One of the following conditions exists for 1 second:
| • | The lateral accelerometer sensor signal voltage is less than 0.15 volts. |
| • | The lateral accelerometer sensor signal voltage is greater than 4.85 volts. |
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 50 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.
-
Tests for the proper operation of the circuit in the low voltage range.
-
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.
-
Tests for a short to voltage in the 5 volt reference circuit.
-
Tests the bias voltage of the lateral accelerometer sensor.
Step | Action | Values | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Antilock Brake System Schematics | ||||||||||
1 | Did you perform the ABS Diagnostic System Check? | -- | Go to Step 2 | |||||||
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 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 Electronic Brake Control Module Replacement . Did you complete the replacement? | -- | Go to Step 16 | -- | ||||||
16 |
Does the DTC reset? | -- | Go to Step 2 | System OK | ||||||
