Data Link Communications

DTC U1000

CIRCUIT DESCRIPTION
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 U1000 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 is in a hybrid ring and star configuration. Each module on the ring has 2 serial data circuits connected to it, except the following modules have only 1 serial data circuit connected them:
- The audio amplifier
- The drive door module (DDM)
- The driver door switch assembly (DDSA)
- The front passenger door module (FPDM)
- The left rear door module (LRDM)
- The memory seat module (MSM)
- The radio antenna module
- The rear integration module (RIM)
- The right rear door module (RRDM)
- The theft deterrent control module
- The TV antenna module
- The vehicle communication interface module (VCIM)

The star has 4 splice packs:
- SP200 located in the left side of the instrument panel, near the steering column, taped to the instrument panel harness.
- SP201 located in the center of the instrument panel, near the radio.
- SP300 located in the left side middle of the passenger compartment, taped to the body harness, near the carpet seam.
- SP303 located in the right rear of the passenger compartment, taped to the body harness, approximately 24 cm (9.5 in) from the fuse block - right rear.

Refer to Data Link Connector (DLC) Schematics.

The following modules and splice packs are connected to the ring portion of the class 2 serial data circuit:
- The dash integration module (DIM)
- The electronic brake control module (EBCM)
- The electronic control module (ECM)
- The inflatable restraint sensing and diagnostic module (SDM)
- The instrument panel cluster (IPC)
- The HVAC control module
- The radio
- The rear integration module (RIM)
- The vehicle communication interface module (VCIM)
- SP200
- SP201
- SP300
- SP303

The following modules are connected to the star portion of the class 2 serial data circuit:
- SP300
- The audio amplifier
- The driver door module (DDM)
- The driver door switch assembly (DDSA)
- The memory seat module (MSM)
- The left rear door module (LRDM)
- SP303
- The antenna module
- The front passenger door module (FPDM)
- The rear integration module (RIM)
- The right rear door module (RRDM)
- The theft deterrent control module
- The vehicle communication interface module (VCIM)

Refer to Data Link Connector (DLC) Schematics and Data Link Communications Description and Operation in order to familiarize yourself with the architecture of the class 2 serial data circuit:

CONDITIONS FOR RUNNING THE DTC
- The following DTCs do not have a current status:
- B1327
- B1328
- U1300
- U1301
- U1305
- 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 the last 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 module ignition cycle counter reaches the reset threshold, 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 XXX Communications is set current. When the modules stop communicating the current DTC U1001-1254 Loss of XXX 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 U1000 or U1255 is set current by the other modules. If the malfunction occurs when the modules are not communicating, only U1000 or U1255 is set.

TEST DESCRIPTION

Steps 1 - 2:

Steps 3 - 4:

Steps 5 - 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 U1000 or U1255.
2. The modules not communicating are the likely cause of 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 U1000 or U1255 may have done so due to some other condition.
14. The module which set U1000 or U1255 is the likely cause of the malfunction.