Operation CHARM: Car repair manuals for everyone.

U1000 - Class II Data Link Malfunction Communication

Diagnostic Chart:




Schematic:




The Class II serial data link is used to communicate information between modules (for example the body control module [BCM] and the powertrain control module [PCM]).

Contained in each modules memory is a list of serial data messages that are important and should be received by the module. Also, contained are the default actions to be taken by the module, if one of the important messages is not received. One of those important messages is the state of health (SOH) message. This message is sent by a module (if no other message needs to be sent) to let all other modules on the serial data link know the sending module is working correctly.

Each time the ignition is turned On, all the modules on the Class II serial data circuit first "learn" the other modules connected to the Class II serial data circuit. Modules are able to "learn" the other modules on the serial data link because each of the important messages contains a source identifier.

This process of "learning" by a module allows the module to know if it has lost communication with a specific module on the Class II data link.

DTC Parameters
The DTC is set when the ignition is turned On and the module did not receive information from any other module on the Class II serial data link.
^ Ignition switch is turned On.
^ Control module was not able to "learn" source identification of another module on Class II data link circuit 18O7 that it relics on for information.
^ Conditions exist for 6 seconds.
^ The PCM cannot communicate with the BCM, the I/P cluster, SDM, or EBTCM.
^ The BCM cannot communicate with the PCM, I/P cluster, SDM, or EBTCM.
^ The SDM cannot communicate with the BCM, PCM, I/P cluster, or EBTCM.
^ The EBTCM cannot communicate with the BCM, I/P Cluster, or SDM.

Diagnostic Aids
^ Check for poor connection at control modules. Inspect harness connectors for backed out terminals, improper terminal mating, broken connector locks, improperly formed or damaged terminals and poor terminal to wire connection (terminal crimped over wire insulation and not conductors).
^ Inspect wiring harness for damage. Check for broken or chaffed insulation.