Scan Tool Does Not Communicate with UART Data Line. GMC Truck Savana 1999

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1999 🢒 Savana 🢒 Body and Accessories 🢒 Data Link Communications 🢒 Scan Tool Does Not Communicate with UART Data Line

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 (DTC's) 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.

Test Description

Refer to SIR Service Precautions before performing SIR system repairs or service.

If the Scan Tool will not function, refer to Scan Tool Inoperative .

If the condition is intermittent, refer to Intermittents and Poor Connections Diagnosis and Testing for Electrical Intermittents in Wiring Systems.

Step	Action	Value(s)	Yes	No
1	Was the SIR Diagnostic System Check performed?	--	Go to Step 2	Go to SIR Diagnostic System Check in SIR
2	Can the scan tool be powered up?	--	Go to Step 3	Go to Scan Tool Inoperative
3	Install the Scan Tool to a similar vehicle. Turn on the ignition leaving the engine off. Attempt to communicate with the SIR module on the UART data line. Does the Scan Tool communicate on the UART data line?	--	Go to Step 5	Go to Step 4
4	Refer to the Scan Tool manufacturer's instruction manual for troubleshooting instructions. Has the troubleshooting / repair been properly completed?	--	Go to SIR Diagnostic System Check in SIR	--
5	Inspect for proper connection/terminal tension of the scan tool to the Data Link Connector terminal 9. Did you find and correct a poor condition?	--	Go to SIR Diagnostic System Check in SIR	Go to Step 6
6	Carefully disconnect the Inflatable Restraint Sensing and Diagnostic Module. Check for poor connection/terminal tension at the Inflatable Restraint Sensing and Diagnostic Module terminal 5. Did you find and correct a poor condition?	--	Go to SIR Diagnostic System Check in SIR	Go to Step 7
7	Test for an open in circuit 800 between the Data Link Connector and the SIR Module Connector. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition?	--	Go to SIR Diagnostic System Check in SIR	Go to Step 8
8	Test for a short to ground in circuit 800 between the Data Link Connector and the SIR Module Connector. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition?	--	Go to SIR Diagnostic System Check in SIR	Go to Step 9
9	Test for a short to B+ in circuit 800 between the Data Link Connector and the SIR Module Connector. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition?	--	Go to SIR Diagnostic System Check in SIR	Go to Step 10
10	Turn the ignition switch to OFF. Replace the Inflatable Restraint Sensing and Diagnostic Module. Refer to Inflatable Restraint Sensing and Diagnostic Module Replacement in SIR. Is the repair complete?	--	Go to SIR Diagnostic System Check in SIR	--