For 1990-2009 cars

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 electronic brake and traction control module (EBTCM), powertrain control module (PCM) and sensing and diagnostic module (SDM) monitor the Class II link for low and high voltage faults.

### DTC Parameters

DTC U1300 will set if the EBTCM, PCM, or SDM detected the Class II circuit in the low state for too long. (Class II circuit shorted to ground) when:

• | Condition exists for longer than 4 seconds for EBTCM, 2 seconds for PCM and SDM.

• | 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 the EBTCM, 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 controller name won't be displayed until the scan tool initially received the correct controller ID over the link upon ignition On.

Important: The BCM CANNOT set U1300.

To locate an intermittent problem, use the 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 ground.