Circuit Description
The transmission control module (TCM), ABS-TCS electronic control module (ECU) and engine control module (ECM) transmit and receive data using the GM LAN serial data protocol, while the body control module (BCM) and other vehicle control modules use the universal asynchronous receive and transmit (UART) serial data protocol.
As the GM LAN and UART protocols are not compatible, a powertrain interface module (PIM) is integrated into the serial data system to enable communication between the two different protocols.
The PIM monitors the UART serial data bus for traffic, and if the PIM does not detect any traffic on the UART serial data bus, DTC U1304 sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC U1304 Loss Communication with UART System
Conditions for Running the DTC
Conditions for running the DTC are:
| • | The ignition is switched ON. |
| • | The ignition voltage is 10-16 V. |
Conditions for Setting the DTC
The PIM does not see any serial data communication on the UART serial data circuit for greater than 10 seconds
Action Taken When the DTC Sets
The module uses default values for all parameters received on the class 2 data circuit.
Conditions for Clearing the DTC
Refer to Diagnostic General Descriptions for information on the conditions for clearing DTCs.
Diagnostic Aids
Refer to Cruise Control Description and Operation for cruise control switch description, operation and inspection procedures. Refer to Cruise Control Schematics , Cruise Control Component Views , and Cruise Control Connector End Views . Refer to Testing for Intermittent Conditions and Poor Connections for intermittent fault conditions
Test Description
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This step checks if the scan tool can communicate with the BCM.
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This step tests the PIM harness connector for serviceability.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Data Link Connector Schematics | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | |
2 |
Does DTC U1304 set this ignition cycle? | Go to Step 3 | System OK |
Using the scan tool, view the body control module (BCM) identification information. Does the scan tool display the BCM identification information? | Go to Step 4 | ||
4 | Using the scan tool, view the BCM Normal Mode Data. Does the scan tool display normal mode data? | Go to Step 5 | Go to Body Control Module (BCM) Programming/RPO Configuration |
5 | Inspect for poor connections at the powertrain interface module (PIM) wiring connector. Has any fault been found and rectified? | Go to Step 7 | Go to Step 6 |
Replace the PIM. Refer to Powertrain Interface Module Replacement . Has the repair been completed? | Go to Step 7 | -- | |
7 |
Does DTC U1304 set this ignition cycle? | Go to Step 2 | System OK |
