For 1990-2009 cars

The class 2 bus shorted generic is configured in a ring used to communicate information between control modules. The controllers on the class 2 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 equal a high state or logic 1. The HVAC control module body control module (BCM), and sensing and OnStar® system Class II link for low and high voltage faults.

### DTC Parameters

DTC U1302 will set if the HVAC control module detected the class 2 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 Diagnostic Trouble Code (DTC) List in Data Link Communications.

• | The SDM will set DTC U1300 for any fault related to the class 2 link circuit. Therefore, if the link is shorted to voltage, the SDM will set DTC U1300 while the HVAC sets DTC 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 2 link located under DIAGNOSTIC CIRCUIT CHECK - - -CLASS 2 MESSAGE MONITOR with the ignition ON, the 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.