Circuit Description
The 5 inputs to the electronic brake control module (EBCM) which are used solely for vehicle stability enhancement are the longitudinal accelerometer, lateral accelerometer, yaw rate sensor, master cylinder pressure sensor and the steering wheel position sensor. The EBCM must detect valid inputs from all 5 sources during the initialization period in order to enable the vehicle stability enhancement system (VSES). Initialization must occur during the first 3000 meters of vehicle travel or 1000 meters of straight vehicle travel. If initialization cannot be achieved during this time period, the VSES remains inactive and the stability system disabled message is displayed. The EBCM does not attempt to reinitialize until the next ignition cycle. One or more DTCs often set, shortly after an unsuccessful initialization attempt, indicating the root cause of the failure. If this occurs, the stability system disabled message is no longer displayed. The service stability system message is displayed instead.
During aggressive driving conditions which repeatedly activate the VSES or traction control system (TCS), one or more of the solenoid coils may become overheated. The stability system disabled message is displayed at this time and the EBCM disables all VSES and TCS brake pressure applications in an attempt to decrease the solenoid temperatures. Coil temperatures are estimated by the EBCM based on ambient temperature and monitored solenoid activation and may not coincide with actual solenoid temperatures. The stability system disabled message turns OFF and normal VSES/TCS activity resumes when the EBCM determines the solenoids have cooled sufficiently.
Diagnostic Aids
If the customer's concern is that the stability system disabled message is displayed intermittently, communicate with the customer to determine what driving conditions are being experienced at the time the message is displayed. The EBCM may be unable to successfully initialize the system during operation on very winding roads. Initialization may also be unsuccessful if pressure is continuously applied to the brake pedal during the initialization period.
The VSES solenoid coils may overheat during aggressive driving, causing the VSES to be disabled temporarily.
A medium-low brake fluid level in the master cylinder reservoir may cause the stability system disabled message to be displayed during stopping or turning maneuvers. This condition will also cause the red brake warning indicator to turn ON. Ensure the master cylinder reservoir has an adequate brake fluid level.
If the message is displayed due to any of the above conditions, no diagnosis or repair of the VSES is required.
Step | Action | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | ||||||||
2 |
Is the stability system disabled message displayed? | Go to Step 3 | Go to Diagnostic Aids | ||||||||
3 | Observe the brake warning indicator on the instrument panel cluster. Is the brake warning indicator always ON? | Go to Brake Warning Indicator Always On in Hydraulic Brakes | Go to Step 4 | ||||||||
4 | Use the scan tool to display VSES History DTCs. Are any of the following DTCs stored in History?
| Go to Step 5 | Go to Step 6 | ||||||||
5 | Operate the vehicle within the Conditions for Running any History DTCs which may be the cause of unsuccessful initialization. Do any of the DTCs listed in step 4 set as a Current DTC? | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | Go to Step 6 | ||||||||
6 |
Do the Digital SWPS Phase A and the Digital SWPS Phase B parameters both transition from Low to High as the steering wheel is rotated? | Go to Step 1 | Go to Step 7 | ||||||||
7 |
Does the scan tool display that both parameters are low? | Go to Step 8 | Go to Step 14 | ||||||||
8 |
Does the scan tool display the Digital SWPS Phase A signal as being High? | Go to Step 11 | Go to Step 9 | ||||||||
9 | Test the battery positive voltage circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 19 | Go to Step 10 | ||||||||
10 | Test the steering wheel position signal A circuit for an open, a high resistance or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 19 | Go to Step 16 | ||||||||
11 |
Does the scan tool display the Digital SWPS Phase B signal as being High? | Go to Step 13 | Go to Step 12 | ||||||||
12 | Test the steering wheel position signal B circuit for an open, a high resistance or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 19 | Go to Step 16 | ||||||||
13 | Test each ground circuit to the steering wheel position sensor for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 19 | Go to Step 15 | ||||||||
14 | Test each steering wheel position sensor signal circuit 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 19 | Go to Step 18 | ||||||||
15 | Inspect for poor connections at the harness connector of the steering wheel position 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 19 | Go to Step 17 | ||||||||
16 | Inspect for poor connections at the harness connector of the electronic brake control module (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 19 | Go to Step 18 | ||||||||
17 | Replace the steering wheel position sensor. Refer to Steering Wheel Position Sensor or Steering Shaft Lower Bearing Replacement in Steering Wheel and Column. Did you complete the replacement? | Go to Step 19 | -- | ||||||||
18 | 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 19 | -- | ||||||||
19 |
Is the stability system disabled message displayed? | Go to Step 3 | System OK |
