SIR Diagnostic System Check

The diagnostic procedures are designed to find and repair SIR faults. To get the best results, it is important to use the diagnostic charts and follow the sequence listed below:
A. PERFORM THE "SIR DIAGNOSTIC SYSTEM CHECK." The "SIR Diagnostic System Check" must be the starting point of any SIR diagnostics. The "SIR Diagnostic System Check" checks for proper "INFL REST" indicator operation, the ability of the DERM to communicate through the serial data line and whether SIR diagnostic trouble codes (DTCs) exist.
B. REFER TO THE PROPER DIAGNOSTIC CHART AS DIRECTED BY THE "SIR DIAGNOSTIC SYSTEM CHECK." The "SIR Diagnostic System Check" will lead you to the correct chart to diagnose any SIR problems. Bypassing these procedures may result m extended diagnostic time, incorrect diagnosis and incorrect part replacements.
C. REPEAT THE "SIR DIAGNOSTIC SYSTEM CHECK" AFTER ANY REPAIR OR DIAGNOSTIC PROCEDURES HAVE BEEN PERFORMED. Performing the "SIR Diagnostic System Check" after all repair of diagnostic procedures will ensure that the repair has been made correctly and that no other fault conditions exist.

CIRCUIT DESCRIPTION
When the ignition switch is first turned to "ON," system voltage is applied from Fuse C-23 to the DERM at the "Ignition 1" input, terminals "A3" and "B3," and from Fuse C-22 to the DERM at the "SIR Indicator High" input, terminal "B9." The DERM responds by flashing the "INFL REST" indicator 7 to 9 times while performing tests on the SIR system.

When the engine is being cranked, system voltage is applied from Fuse C-21 to the DERM at the "Crank" input, terminal "B10." The DERM responds by grounding the "SIR Indicator Low" output until system voltage is removed from the "Crank" input.

This results in the "INFL REST" indicator being illuminated steady during cranking.

After cranking, the DERM will again flash the "INFL REST" indicator 7 to 9 times and perform tests on the SIR system.

NOTES ON SYSTEM CHECK CHART
1. The INFL REST" indicator should flash 7 to 9 times after the ignition switch is first turned to "ON."
2. The "INFL REST" indicator should remain illuminated steady during cranking.
3. After cranking, the "INFL REST" indicator should flash 7 to 9 times and then remain off
4. The "INFL REST" indicator has successfully completed the "Bulb Check."
5. This test checks for the proper operation of the "Serial Data" circuit. This test will also determine whether history DTCs are stored and what they are.
6. Improper operation of the "INFL REST" indicator is indicated. This test differentiates an indicator remains illuminated from an indicator does not illuminate condition.
7. This test differentiates a current DTC exists condition from a diagnostics enabled when not requested condition.
8. The "INFL REST" indicator has completed the "Bulb Check" and indicates current DTCs exist.
9. This test checks for proper operation of the "Serial Data" circuit. This test will also indicate what DTCs are stored and whether they are current or history.

DIAGNOSTIC AIDS
The order in which DTCs are diagnosed is very important. Failure to diagnose the DTCs in the order specified may result in extended diagnostic time, incorrect diagnosis and incorrect part replacements.