U2100
DTC U2100
CIRCUIT DESCRIPTION
Modules connected to the GMLAN serial data circuit monitor for serial data communications on the GMLAN network during normal vehicle operation. Operating information and commands are exchanged among the modules. The body control module (BCM) maintains a transmit error counter (TEC) and a receive error counter (REC). The counter values increase with detected errors and will decrease with error-free messages. If the TEC value exceeds 255 the BCM removes itself from the high speed GMLAN network and a DTC U2100 will be set.
DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC U2100 High Speed CAN Communication Bus
CONDITIONS FOR RUNNING THE DTC
- Voltage supplied to the module is in the normal operating voltage range.
- The vehicle power mode requires serial data communication to occur.
CONDITIONS FOR SETTING THE DTC
A certain number of no valid transmitted messages on the GMLAN serial data circuits are detected by the module. 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
ACTION TAKEN WHEN THE DTCS SETS
- The module suspends all message transmission.
- The module uses default values for all parameters received on the high speed GMLAN serial data circuits.
- The module inhibits the setting of all other high speed GMLAN 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
The BCM can set this DTC as current because it is the gateway between the class 2 and high speed GMLAN serial data circuits, and the BCM diagnostics is performed on class 2 data link. Refer to Data Link Communications Description and Operation for more information about data link communication.
The high speed GMLAN serial data bus uses two 120 ohm terminating resistors that are in parallel with the high speed GMLAN (+) and (-) circuits. One of the resistors is connected at the BCM and the other is at the engine control module (ECM). When testing for a short between high speed GMLAN (+) and (-) a reading of 60 ohm is normal. If the high speed GMLAN serial data is open testing the resistance between high speed GMLAN (+) and (-) will read about 120 ohm.
TEST
