U1302

CIRCUIT DESCRIPTION
The Class II bus shorted generic 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 to 7 volts for communication. Zero volts equals a low state or logic "0" and 7 volts equal a high state or logic "1". The HVAC control module body control module (BCM), and sensing and Onstar(R) system Class II link for low and high voltage faults.

DTC PARAMETERS
DTC U1302 will set if the HVAC control module detected the Class II circuit shorted circuit 1807.
^ Condition exists for longer than 3 seconds
^ Ignition is On

DTC U1302 diagnostic runs continuously with ignition On.

DTC U1302 is a type C DTC.

DIAGNOSTIC AIDS

IMPORTANT: When this code sets, refer to the "Data Link Communications".

If the Scan tool can communicate with the BCM, PCM or SDM, then the Class II link is not currently shorted.

NOTE: 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 HVAC sets U1302. Inspect the wiring harness for signs of chafing or broken insulation.

To locate an intermittent problem, use Scan tool to monitor any of the controllers on the Class II link located under DIAGNOSTIC CIRCUIT CHECK ---CLASS II MESSAGE MONITOR with ignition On, engine Off. INACTIVE will be displayed on all controllers if the link is shorted to voltage.

IMPORTANT: The controller name won't be displayed until the Scan tool initially received the correct controller ID over the link upon ignition On.

TEST

Diagnostic Chart: