U1255

CIRCUIT DESCRIPTION
Modules connected to the Class 2 data link monitor the link for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. In addition to this, Node Alive (State of Health) massages are transmitted by each module on the data link about once every 2 seconds. When the Body Control Module (BCM) and radio receiver detects no messages on the Class 2 data link, U1255 is set.

CONDITIONS FOR SETTING THE DTC
^ Voltage supplied to the modules are in the normal operating voltage range (approximately 9-16 volts).
^ No Class 2 messages are detected on the data link.

CONDITIONS FOR CLEARING THE DTC
^ A current U1255 will clear when a valid Class 2 message is detected on the data link or at the end of the current ignition cycle.
^ A history U1255 will clear upon receipt of a scan tool CLEAR DTCs command.

DIAGNOSTIC AIDS
^ This DTC cannot be retrieved with a current status. Diagnosis of a current U1255 is accomplished via the symptom, Scan Tool Will Not Communicate With the Class 2 Serial Data Line.
^ An intermittent condition is likely to be caused by a short to ground on the Class 2 serial data line.
^ To assist in diagnosis, refer to Wiring Systems and the DLC schematics.