Scan Tool Does Not Communicate With UART Data Line

Diagnostic Chart:

CIRCUIT DESCRIPTION
The UART Serial Data Line is used for communication with the SIR Module. The UART line relies on a 5 volt digital signal for the exchange of data between different control modules and to provide Scan Tool diagnostic data. When the ignition switch is in the RUN position and the UART line is at rest, i.e., no communication is taking place, the voltage remains HIGH at approximately 5 volts.When data is transmitted the voltage is pulled to ground, approximately 0 volts. The Supplemental Inflatable Restraint System's Sensing and Diagnostic Module (SDM) utilizes UART communications. The Scan Tool may be used to retrieve, view, and clear Diagnostic Trouble Codes (DTCs) stored in the SDM. The Scan Tool also uses the UART line to receive serial data from the SDM.
A loss of UART communications would prevent the Scan Tool from communicating with the SDM during SIR system diagnosis.

DIAGNOSTIC AIDS

IMPORTANT: Refer to SIR Service Precautions before doing SIR system repairs or service.

1. If the Scan Tool will not function, refer to Scan Tool Does Not Power Up
2. If the condition is intermittent, refer to Testing for Intermittent and Poor Connections and Testing for Electrical Intermittents.