Circuit Description
The Class II serial data link is configured in a ring used to communicate information between control modules. The controllers on the Class II link use a variable pulse width modulated square wave of 0-7 volts for communication. Zero volts equals a low state or logic "0" and 7 volts equals a high state or logic "1". The body control module (BCM), powertrain control module (PCM) and sensing and diagnostic module (SDM) monitor the Class II link for low and high voltage faults.
Conditions for Setting the DTC
DTC U1300 will set if the BCM, PCM or SDM detected the Class II circuit in the low state for too long -- Class II circuit shorted to ground -- when:
| • | The condition exists for longer than 3 seconds. |
| • | The ignition is On. |
DTC U1300 diagnostic runs continuously with ignition On.
DTC U1300 is a type C DTC.
Diagnostic Aids
If the scan tool can communicate with either the BCM, PCM or SDM, then the Class II link is not currently shorted to ground.
Inspect the wiring harness for signs of chafing or broken insulation.
Important:
• The SDM will set U1300 for any fault related to the Class II
link circuit. Therefore, if the link is shorted to voltage, the SDM will set U1300
while the BCM sets U1301. • The controller name will not be displayed until the scan tool initially
received the correct controller ID over the link upon ignition On.
To locate an intermittent problem, use a scan tool to monitor any of the controllers on the Class II link located under the DIAGNOSTIC CIRCUIT CHECK---CLASS II MESSAGE MONITOR with the ignition On and the engine Off. INACTIVE will be displayed on all controllers if the link is shorted to ground.
