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Scan Tool Does Not Communicate With UART Data Line

  1. Perform SIR diagnostic system check. See SIR DIAGNOSTIC SYSTEM CHECK under DIAGNOSTIC TESTS in AIR BAG RESTRAINT SYSTEM - TRUCKS article in RESTRAINTS.
  2. Turn ignition to RUN. Measure voltage with DVOM between DLC terminals No. 4 and 9. If voltage is less than 5 volts, go to next step. If voltage is greater than 5 volts, go to step  5. If voltage is 5 volts, perform SIR diagnostic system check. See SIR DIAGNOSTIC SYSTEM CHECK under DIAGNOSTIC TESTS in AIR BAG RESTRAINT SYSTEM - TRUCKS article in RESTRAINTS.
  3. Turn ignition to OFF. Check for continuity using DVOM between ground and DLC terminal No. 9. If there is continuity, go to next step. If there is no continuity, go to step  7.
  4. Repair short to ground in Tan 800 circuit wiring between SDM and DLC. Perform SIR diagnostic system check. See SIR DIAGNOSTIC SYSTEM CHECK under DIAGNOSTIC TESTS in AIR BAG RESTRAINT SYSTEM - TRUCKS article in RESTRAINTS.
  5. Disconnect SDM connector. Turn ignition to RUN. Check voltage using DVOM between ground and DLC terminal No. 9. If voltage is greater than 0 volts, go to next step. If voltage is 0 volts, go to step  7.
  6. Repair short to voltage in Tan 800 circuit wiring between SDM and DLC. Perform SIR diagnostic system check. See SIR DIAGNOSTIC SYSTEM CHECK under DIAGNOSTIC TESTS in AIR BAG RESTRAINT SYSTEM - TRUCKS article in RESTRAINTS.
  7. Perform SDM integrity check. See SDM INTEGRITY CHECK under DIAGNOSTIC TESTS in AIR BAG RESTRAINT SYSTEM - TRUCKS article in RESTRAINTS. If SDM checks faulty, replace SDM. See REMOVAL & INSTALLATION in AIR BAG RESTRAINT SYSTEM - TRUCKS article in RESTRAINTS.
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