For 1990-2009 cars

### Class 2 Serial Data

The Class 2 serial data link allows the modules below to transmit, receive, or exchange data with the scan tool:

• | powertrain control module (PCM) L18/8.1 gas engine

• | transmission control module (TCM) LG5/7.2 diesel engine

### 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 messages are transmitted by each module on the class 2 serial data circuit about once every 2 seconds. When the module detects the class 2 serial data circuit shorted, the setting of all other class 2 serial communication DTCs is inhibited and a U1300, U1301, or a U1305 DTC will set.

### Universal Asynchronous Transmitter Receiver (UART) Data Line

Circuit 799 exists pin 12 of the DLC, and is a dedicated communication link between the EBCM and the scan tool. When a communication failure exists with the EBCM, this circuit should be checked. This UART circuit can exist alone, or in conjunction with class 2 serial data communication information, depending on the vehicle, functions/RPOs.