Modules connected to the high speed GMLAN serial data circuits monitor for serial data communications on the high speed GMLAN network during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module detects a bus-off condition a DTC U0001, U2100 or U2104 will be set. Generally these DTCs can be retrieved as history only, with the exception of body control module (BCM) that can set DTC U2100 as current, because it communicates with the scan tool on class 2.
Diagnostic Aids
The high speed GMLAN serial data bus uses two 120 ohms terminating resistors that are in parallel with the high speed GMLAN (+) and (-) circuits. One of the resistors is connected at the body control module (BCM) and the other is at the engine control module (ECM). If testing for a short between high speed GMLAN (+) and (-) a reading of 60 ohms is normal. If the high speed GMLAN serial data is open testing the resistance between high speed GMLAN (+) and (-) will read about 120 ohms.
The engine will not start when there is a total malfunction of the high speed GMLAN serial data circuits while the engine is not running. The following conditions may cause a total loss of high speed GMLAN data communication:
| • | A short between high speed GMLAN (+) and high speed GMLAN (-) circuits |
| • | Any of the high speed GMLAN serial data circuits shorted to ground or voltage |
| • | A module internal malfunction that causes a short to voltage or ground on the high speed GMLAN circuits |
| • | Any of the high speed GMLAN serial data circuits open |
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 - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | ||||||||
2 |
Did you record DTC U2100 , as current? | Go to DTC U2100 | Go to Step 3 | ||||||||
3 | Did you record any DTCs in the range of U2105 to U2199? | Go to DTC U2105-U2199 | Go to Step 4 | ||||||||
4 |
Important:: Make sure the CANdi module works fine. When functioning properly, CANdi's LED flashes. In the event of a problem, the LED will be constantly illuminated. Does the scan tool communicate with any module on the GMLAN serial data circuits? | Go to Step 5 | Go to Step 7 | ||||||||
5 | Retrieve DTCs from the respective module(s). Did you record any DTCs in the range of U0100 to U0299 or in the range of U2105 to U2199? | Go to DTC U0100-U0299 or DTC U2105-U2199 | Go to Step 6 | ||||||||
6 |
Important:: Turn ON the ignition, with the engine OFF, when testing for a short to voltage. Use the DMM MIN/MAX function to capture intermittent conditions.
Refer to the following in Wiring Systems: Did you find and correct the condition? | Go to Step 13 | Go to Diagnostic Aids | ||||||||
7 |
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 8 | ||||||||
8 | Test the ground circuits of the BCM for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 9 | ||||||||
9 | Inspect for poor connections at the DLC terminals 6 and 14. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 10 | ||||||||
10 | Test the high speed GMLAN serial data circuits between the BCM and DLC for:
Refer to the following in Wiring Systems: Did you find and correct the condition? | Go to Step 13 | Go to Step 11 | ||||||||
11 | Inspect for poor connections at the high speed GMLAN serial data circuits of the BCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 13 | Go to Step 12 | ||||||||
12 | Replace the BCM. Refer to Control Module References for replacement, setup and programming. Did you complete the replacement? | Go to Step 13 | -- | ||||||||
13 |
Did you record any current DTCs? | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | System OK | ||||||||
