Circuit Description
The controller area network (CAN) serial data line is a high speed serial data bus used to communicate information between the engine control module (ECM), body control module (BCM), and the transmission control module (TCM). Typical data-transmission speeds must be high enough to ensure the required real-time response is maintained. The CAN serial data line does not communicate with the scan tool via the data link connector (DLC). CAN serial data information is interpreted by the BCM and transmitted to the serial data line by the BCM. The CAN bus is continuously monitored by the modules on the serial data bus.
DTC Descriptors
This diagnostic procedure supports the following DTCs:
| • | U2103 Fewer Controllers On Bus Than Programmed |
| • | U2104 Controller Area Network (CAN) Bus Reset Counter Overrun |
Conditions for Running the DTCs
| • | Supply voltage to the modules are in the normal operating range. |
| • | The ignition is cycled from OFF to RUN. |
Conditions for Setting the DTC
DTC U2103
The module has lost communication with a learned module on the serial data bus.
DTC U2104
The module detects an error on the serial data bus.
Action Taken When the DTCs Sets
| • | The module suspends all message transmission. |
| • | The module uses default values for all parameters received on the serial data circuits. |
| • | The module inhibits the setting of all other communication DTCs. |
Conditions for Clearing the DTC
| • | A current DTC clears when the malfunction is no longer present. |
| • | A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction. |
Diagnostic Aids
| • | DTC U2103 is likely an intermittent condition caused by a open on the GMLAN serial data circuits. Use the Scan Tool Does Not Communicate with High Speed GMLAN Device procedure in order to isolate an intermittent condition. |
| • | DTC U2104 cannot be retrieved with a current status. Diagnosis of current DTC is accomplished via the symptom, Scan Tool Does Not Communicate with High Speed GMLAN Device. |
Step | Action | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Data Link Connector Schematics Connector End View Reference: Master Electrical Component List in Wiring Systems | |||||||||||
1 | Did you perform the Diagnostic System Check for the system exhibiting the symptom? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | ||||||||
2 |
Does the scan tool indicate that DTC U2100 sets as either a current or history DTC? | Go to DTC U2100 | Go to Step 3 | ||||||||
3 |
Important: Turn the ignition ON, with the engine OFF when testing for a short to voltage. Use a DMM MIN/MAX function to capture intermittent conditions. Test the controller area network (CAN) serial data circuits for the following:
Refer to the following in Wiring Systems: Did you find and correct the condition? | Go to Step 6 | Go to Step 4 | ||||||||
4 | Inspect for poor connections at the harness connector of the module that is not communicating. Did you find and correct the condition? | Go to Step 6 | Go to Step 5 | ||||||||
5 |
Important: Perform the programming or setup procedure for the replaced control module if required. Replace the control module that is not communicating. Refer to Control Module References for the applicable replacement procedure. Did you complete the replacement? | Go to Step 6 | -- | ||||||||
6 |
Does the DTC reset? | Go to Step 2 | System OK | ||||||||
