Data Link Communications

DTC U1000

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 that contains a critical operating parameter, the module records the identification number of the module which sent the message. If a module does not associate an identification number with every critical parameter within 5 seconds of beginning serial data communication, DTC U1000 or U1255 will set.

DTC DESCRIPTORS
This diagnostic procedure supports the following DTCs:
- DTC U1000 Class 2 Data Link
- DTC U1255 Class 2 Data Link

CONDITIONS FOR RUNNING THE DTC
- Battery Voltage is 9-16 Volts.
- DTCs U1300, U1301, or U1305 are not current.
- The vehicle power mode requires serial data communication to occur.

CONDITIONS FOR SETTING THE DTC
A message containing a critical operating parameter has not been received within 5 seconds after establishing class 2 serial data communication.

ACTION TAKEN WHEN THE DTC SETS
The module uses a default value for the missing parameter.

CONDITIONS FOR CLEARING THE DTC
- A current DTC clears when the malfunction is no longer present.
- A history DTC clears when the ignition has been cycled 100 times, without a repeat of the malfunction.

DIAGNOSTIC AIDS
When a malfunction such as an open fuse to a module occurs while modules are communicating, a DTC U1001-1254 Loss of Communications is set. When the modules stop communicating, the current DTC U1001-1254 Loss of Communications is cleared but the history DTC remains. When the modules begin to communicate again, the module with the open fuse will not be learned by the other modules so DTC U1000 or U1255 is set current by the other modules. If the malfunction occurs when the modules are not communicating, only DTC U1000 or U1255 is set.

TEST DESCRIPTION

Steps 1 - 2:

Steps 3 - 4:

Step 5:

Step 6:

Steps 7 - 11:

Steps 12 - 14:

The numbers below refer to the step numbers on the diagnostic table.
1. A DTC U1001 - U1254 Lost Communications with XXX with a history status may indicate the cause of DTC U1000 or U1255.
2. The modules not communicating are the likely cause of DTC U1000 or U1255. The modules that are available on the class 2 serial data circuit are listed in the Circuit Description.
6. The module which was not communicating due to a poor connection to the class 2 serial data circuit may have set DTC U1001 - U1254 Lost Communications with XXX for those modules that it was monitoring.
9. The modules which can communicate indicate the module which cannot communicate. You must clear the serial data communication DTCs from these modules to avoid future misdiagnosis.
12. If all modules are communicating, the module which set DTC U1000 or U1255 may have done so due to some other condition.
14. The module which set DTC U1000 or U1255 is the likely cause of the malfunction.