Data Link Communications
DTC U1OOO and U1255Circuit Description
The powertrain interface module (PIM) receives information from the powertrain control module (PCM) on the class 2 serial data circuit. If there is a problem with this circuit or the PCM is not communicating, the RIM will detect this lack of information and will set a DTC. Also, if there is a problem with the serial data circuit, performing the Powertrain (OBD) System Check will lead you to the Data Link Connector Diagnosis.
Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for State of Health monitoring. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. When a module does not associate an identification number with at least one critical parameter within 5 seconds of beginning serial data communication, DTC U1OOO or U1255 DTC is set. When more than one critical parameter does not have an identification number associated with it, the DTC will only be reported once.
The class 2 serial data communications circuit on this vehicle consists only of the communication circuit between the PCM and the PIM.
The PIM converts the Class 2 signal to UART which is then transmitted among the following modules:
- The radio
- The Sensing and Diagnostic module (SDM)
- The Body Control Module (BCM)
- The Electronic Brake Control Module (EBCM)
- The Instrument Panel Cluster (IPC)
Conditions for Running the DTC
- The ignition switch is ON.
- The ignition voltage is between 5-17 volts
Conditions for Setting the DTC
- The PIM does not receive any class 2 serial data communication for greater than five seconds.
Action Taken When the DTC Sets
- The Check Powertrain MIL will not be activated.
Conditions for Clearing the MIL/DTC
- A Last Test Failed (current DTC) clears, after the ignition has been cycled and the PIM receives Class 2 serial data.
- Use the scan tool to clear the DTC.
Diagnostic Aids
The following problems may cause this DTC to set:
- Poor connections/terminal tension at the BCM.
- Poor connections/terminal tension at the PIM.
DTC U1000 And U1255 (1 Of 2):
DTC U1000 And U1255 (2 Of 2):
Test Description
The numbers below refer to the step numbers on the diagnostic table.
1. A DTC U1OO1-U1254 Lost Communications with XXX with a history status may indicate the cause of U1OOO or U1255.
2. The modules not communicating are the likely cause of U1OOO 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 U1OO1-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 U1OOO or U1255 may have done so due to some other condition.
14. The module which set U1OOO or U1255 is the likely cause of the malfunction.