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. In addition to this, Node
Alive (State of Health) messages are transmitted by each module on the
class 2 serial data circuit about once every two seconds. When the module
detects no messages and a high voltage on the Class 2 serial data link
for approximately three seconds, U1301 is set and the setting of all other
class 2 serial communication DTCs is inhibited.
Conditions for Running the DTC
| • | Voltage supplied to the module is in the normal operating voltage
range (approximately 9 to 16 volts). |
| • | The vehicle power mode (ignition switch position) requires serial
data communication to occur. |
Conditions for Setting the DTC
| • | No valid class 2 messages are detected on the class 2 serial
data circuit. |
| • | The voltage level detected on the class 2 serial data circuit
is high. |
| • | The above conditions are met for approximately three seconds. |
Action Taken When the DTC Sets
| • | The module inhibits the setting of all other class 2 DTCs. |
| • | The module uses default values for all parameters received on
the class 2 serial data circuit. |
Conditions for Clearing the DTC
| • | A current U1301 will clear when a valid class 2 message is detected
on the class 2 serial data circuit or at the end of the current ignition cycle. |
| • | A history U1301 will clear upon receipt of a scan tool Clear
DTCs command. |
Diagnostic Aids
| • | An intermittent condition is likely to be caused by a short to
voltage on the class 2 serial data circuit. Use the Scan Tool Does Not Communicate
with a Class 2 Device procedure in order to isolate an intermittent condition.
Refer to
Scan Tool Does Not Communicate with Class 2 Device |
