Circuit Description
The link for serial data communications during normal vehicle operation
is monitored by modules connected to the Class 2 serial data link.
Operating information and commands are exchanged among the modules. The Node
Alive (State of Health) messages are transmitted by each module on the Class 2
serial data link about once every 2 seconds. The U1301 is set. When
the module detects no messages and a high voltage on the Class 2 serial
data link for approximately 3 seconds, all of the other Class 2
serial communication DTCs are set.
Conditions for Setting the DTC
| • | Voltage is supplied to the module in the normal operating voltage
range of approximately 9-16 Volts. |
| • | No valid Class 2 messages are detected on the Class 2
serial data link. |
| • | The voltage level detected on the Class 2 serial data link
is high. |
| • | The above conditions are all met simultaneously for 3 seconds. |
Action Taken When the DTC Sets
| • | The module inhibits the setting of all other Class 2 DTCs. |
| • | DTC U1301 is set by the module. |
Conditions for Clearing the DTC
| • | When a valid Class 2 message is detected on the Class 2
serial data link or at the end of the current ignition cycle, a current U1301
will clear. |
| • | A history U1301 will clear upon receipt of a scan tool CLEAR DTCs
command. |
Diagnostic Aids
This DTC may not be retrieved with a current status. Diagnosis of a
current U1255 is accomplished via the symptom. The scan tool will not communicate
with a Class 2 device. An intermittent condition is likely to be caused
by a short to voltage on the Class 2 serial data link.
