Circuit Description
Modules connected to the Class 2 data link monitor the link for serial
data communications during normal vehicle operation. Operating information
(Report messages) and commands (Load messages) are exchanged among the
modules. Also, node alive State Of Health (SOH) messages are transmitted
by each module on the data link about once every two seconds. When the
SDM detects no messages on the Class 2 data link, U1255 is set.
Conditions for Setting the DTC
| • | Voltage supplied to the SDM is in the normal operating voltage
range (approximately 9-16 volts). |
| • | No class 2 messages are detected by the SDM on the data link. |
Action Taken When the DTC Sets
The SDM sets DTC U1255.
Conditions for Clearing the MIL/DTC
The DTC will clear when one of the following conditions is met:
| | The SDM receives a valid Class 2 message or the ignition switch is turned
to the OFF position. |
| | You issue a scan tool CLEAR CODES 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. |
