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 RUN, each module communicating on the serial data line sends a State of Health (SOH) message every two seconds (one second for the PCM) to ensure that the system is operating properly. When the Powertrain Control Module (PCM) stops communicating on the Class 2 serial data line, for example if the PCM loses power or ground, the SOH message it normally sends on the serial data line every one second disappears. This module, which expects to receive that SOH message, detects its absence; this module in turn sets an internal DTC U1016 associated with the loss of SOH of the PCM, which is no longer communicating on the Class 2 serial data line.
Conditions for Setting the DTC
- The module does not receive a State of Health (SOH) message back from the PCM for 5 seconds.
- This DTC only sets if RIM DTC B1328, B1327, U1300, U1301 or DIM DTC B1982, B1983, U1300, U1301 is not current in module memory.
Action Taken When the DTC Sets
| • | DTC U1016 is stored in module memory. |
| • | The module reverts to values for the information it normally receives from the PCM to continue uninterrupted operation. |
| • | This DTC does not cause a driver warning message to appear. |
| • | This may result in an outside temperature display which is significantly higher than actual. |
Conditions for Clearing the DTC
| • | This DTC clears (status changes from current to history) under any of the following conditions: |
| - | The module detects a State of Health Message from the PCM. |
| - | 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 U1016 does not represent a failure within the module that set it. |
| • | 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 U1016 is stored in module 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 U1016. 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 Body Control Module Diagnostic System Check before continuing with the diagnosis of this DTC.
-
U1016 is the result of loss of communication with the Powertrain Control Module (PCM). Note that other modules on the Class 2 serial data line may also set U1016 if the PCM is not communicating on the serial data line. Refer to Data Link Connector in Wiring Systems to identify all modules which may set U1016.
-
Clear all DTCs after the repair procedure is complete.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Body Control Module Diagnostic System Check performed? | -- | Go to Body Control Module Diagnostic System Check | ||
Attempt to establish communication with the Powertrain Control Module (PCM) using a scan tool. Does the scan tool communicate with the PCM? | -- | Go to Engine 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 Body Control Module Diagnostic System Check | -- |
