Circuit Description
The Class 2 serial data line is used to communicate information between modules. Each module connected to the serial data line is assigned its own recognition code (address). This code is used to identify which modules are communicating. Modules communicate with each other by periodically sending State of Health (SOH) messages. When the ignition switch is in ON, each module communicating on the serial data line sends a State of Health (SOH) message every two seconds to ensure that the system is operating properly. When the Continuously Variable Road Sensing Suspension (CVRSS) Module stops communicating on the Class 2 serial data line, for example if the CVRSS Module loses power or ground, the SOH message it normally sends on the serial data line every two seconds disappears. The Electronic Brake and Traction Control Module (EBTCM), which expects to receive that SOH message, detects its absence; the EBTCM in turn sets an internal DTC U1056 associated with the loss of SOH of the CVRSS, which is no longer communicating on the Class 2 serial data line.
Conditions for Setting the DTC
| • | The EBTCM does not receive a State of Health (SOH) message back from the CVRSS Module. (The EBTCM retries the request three times, then sets DTC U1056.) |
| • | This DTC only sets if DTC B1982, B1983, U1300 or U1301 is not current in EBTCM memory. |
Action Taken When the DTC Sets
| • | DTC U1056 is stored in EBTCM memory. |
| • | The EBTCM uses the default values for the initialization data. |
| • | This DTC does not cause a driver warning message to appear. |
Conditions for Clearing the DTC
| • | This DTC clears (status changes from current to history) under any of the following conditions: |
| - | The EBTCM detects a State of Health Message from the CVRSS Module. |
| - | On each ignition cycle. |
| • | A history DTC clears after 50 consecutive ignition cycles if the conditions for setting the DTC are no longer present. |
| • | Use the On-Board clearing DTCs feature. Refer to Diagnostic Trouble Code (DTC) Clearing in HVAC Systems with A/C - Automatic. |
| • | Use a scan tool. |
Diagnostic Aids
| • | DTC EBTCM U1056 does not normally represent a failure within the EBTCM. |
| • | When Loss of Class 2 Serial Data Communication DTCs (DTCs with the letter U as the prefix) are stored as history DTCs, know all possible serial data DTCs set in each module before diagnosing the serial data line. |
| • | If U1056 is stored in EBTCM memory, check for the same DTC stored in other modules capable of storing this DTC. The Data Link Connector (DLC) circuit description provides a chart which indicates which modules may set U1056. Refer to Data Link Connector (DLC) in Wiring Systems. |
| • | If the DTC is a history DTC, the problem may be intermittent. |
Test Description
The numbers below refer to the step numbers on the diagnostic table:
-
Perform the ABS Diagnostic System Check in Brakes before continuing with the diagnosis of this DTC.
-
U1056 is the result of loss of communication with the Continuously Variable Road Sensing Suspension (CVRSS) Module. Note that the Electronic Brake and Traction Control Module (EBTCM) is the only module which may set this DTC.
-
Clear all DTCs after the repair procedure is complete.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Suspension Controls Diagnostic System Check performed? | -- | Go to Suspension Controls Diagnostic System Check | ||
Attempt to establish communication with the Continuously Variable Road Sensing Suspension (CVRSS) Module using a scan tool. Does the scan tool communicate with the module? | -- | Go to Suspension Controls | ||
3 | Check and repair the Class 2 serial data line CKT 1807 (PPL) for intermittent conditions. Refer to Intermittents and Poor Connections . Is the wiring repair complete? | -- | -- | |
Are all DTCs cleared? | -- | Go to Suspension Controls Diagnostic System Check | -- |
