Circuit Description
Each module connected to the class 2 serial data circuit monitors serial data communication during normal vehicle operation. Operating parameters and other information are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for state of health monitoring. Once a module learns another modules identification number, it will monitor the serial data for that modules node alive message. Each module that sends critical operating parameters is required to send a node alive message every two seconds. When no message is detected from a learned module for 5 seconds, DTC U1001-U1254 will set.
DTC Descriptors
This diagnostic procedure supports the following DTCs.
| • | DTC U1016 Lost Communications With Engine Control System (PCM) |
| • | DTC U1040 Lost Communications With Electronic Brake Control Module (EBCM) |
| • | DTC U1064 Lost Communications With Body Control Module (BCM) |
| • | DTC U1088 Lost Communications With Restraints Control System (SDM) |
| • | DTC U1128 Lost Communications With Radio |
| • | DTC U1176 Lost Communications With Remote Function Actuation (RCDLR) |
Conditions for Running the DTC
| • | Battery Voltage is 9-16 volts. |
| • | DTCs U1300, U1301, or U1305 are not current. |
| • | Serial data communication has begun. |
Conditions for Setting the DTC
A node alive message from a learned module has not been detected for 5 seconds.
Conditions for Clearing the DTC
| • | A current DTC clears when the malfunction is no longer present, or when the ignition is cycled. |
| • | A history DTC clears when the ignition has been cycled 100 times, without a repeat of the malfunction. |
Diagnostic Aids
When more than one Loss of Communication DTC is set in a single module or among multiple modules, diagnose the DTCs in the following order:
- Current DTCs before history DTCs, except as specified in the diagnostic tables.
- The DTC which is reported the most times.
- From the lowest number DTC to the highest number DTC.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
The module that was not communicating due to an open in the class 2 serial data circuit may have set Loss of Communication DTCs for those modules that it was monitoring.
-
The modules that can communicate indicate the module which cannot communicate. You must clear the DTCs from these modules to avoid future misdiagnosis.
Step | Action | Yes | No | ||||
|---|---|---|---|---|---|---|---|
Schematic Reference: Data Link Connector Schematics Connector End View Reference: Master Electrical Component List and Inline Harness Connector End Views in Wiring Systems | |||||||
1 | Test the battery positive voltage and ignition voltage circuits of the module that is not communicating for a high resistance an open or a short to ground. Refer to the following:
Did you find and correct the condition? | Go to Step 6 | Go to Step 2 | ||||
2 |
Did you find and correct the condition? | Go to Step 6 | Go to Step 3 | ||||
3 | Inspect for poor connections at the battery positive voltage circuits, the ignition voltage circuits, the ground circuit, and the class 2 serial data circuit of the module that is not communicating. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems for the proper procedure. Did you find and correct the condition? | Go to Step 6 | Go to Step 4 | ||||
4 | Test the class 2 serial data circuit of the module that is not communicating for an open. Refer to the following:
Did you find and correct the condition? | Go to Step 6 | Go to Step 5 | ||||
5 | Replace the module that is not communicating. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 6 | -- | ||||
Does the scan tool display any DTCs that do not begin with a U? | Go to Step 7 | ||||||
7 | Clear the DTCs with the scan tool. Did you complete the action? | Go to Step 8 | -- | ||||
Select the Display DTCs function for the modules which had the Loss of Communications DTC set. Does the scan tool display any DTCs which do not begin with a U? | Go to Step 9 | ||||||
9 | Continue diagnosing or clearing the DTCs until all the modules have been diagnosed and all the DTCs have been cleared. Did you complete the action? | System OK | -- | ||||
