For 1990-2009 cars

Caution: In order to avoid deploying the air bag when troubleshooting the SIR system, use only the equipment specified in this manual and the instructions given in this manual. Failure to use the specified equipment as instructed could cause air bag deployment, personal injury to you or someone else, or unnecessary SIR system repairs.

The SIR Diagnostic System Check must always be the starting point of any SIR system diagnosis. The SIR Diagnostic System Check tests for the correct operation of the AIR BAG warning lamp, and tests for SIR Diagnostic Trouble Codes (DTC) using the scan tool. The following describes the difference between current DTCs and history DTCs:

• | Current DTCs -- Malfunctions that are presently being detected. Random-Access Memory (RAM) stores the current DTCs. Turning the ignition switch to the OFF position erases current DTCs. The presence of a current DTC will cause the inflatable restraint Sensing and Diagnostic Module (SDM) to turn ON the AIR BAG warning lamp.

• | History DTCs -- All malfunctions that are detected since last clearing of history memory. Electrically Erasable Programmable Read Only Memory (EEPROM) stores the history DTCs. A scan tool CLEAR CODES command will erase history DTCs.

#### Scan Tool Diagnostics

A scan tool is used in order to read current diagnostic trouble codes and history diagnostic trouble codes. Verify the scan tool contains updated software before attempting to communicate with the SIR system. Connect the tool to the OBD 2 data link connector, and turn the ignition switch to the ON position. The scan tool reads Serial Data from the inflatable restraint Sensing and Diagnostic Module (SDM) Serial Data output terminal 1 to the OBD 2 DLC terminal 9.

The scan tool displays information that the SDM sends to the scan tool over the UART serial data line. Refer to Scan Tool Data List .

#### Flash DTC Diagnostics

Flash DTC diagnostics read the current DTCs, and determine the present history DTCs. You can enable flash DTC diagnostics by jumping the terminals of the Air Bag Diagnostic Connector with the ignition switch set to the ON position. This action pulls the SDM terminal 12 to ground and signals the SDM to enter the flash DTC diagnostic display mode.

The SDM displays the DTCs by flashing the AIR BAG warning lamp. The number of times that the warning lamp flashes indicates the numerals of the DTC code.

1. Count the number of flashes that occur in the first series of flashes.This number is the first digit of the DTC code.
2. The lamp will pause for a half of a second.
3. Count the number of flashes that occur in the second series of flashes.This number is the second digit of the DTC code.

Each DTC is flashed once before moving on to the next DTC. After the tool displays all DTCs, the entire DTC sequence is repeated until you remove the jumper from the Air Bag Diagnostic Connector.

Two special DTCs exist, DTC 12 and DTC 13. DTC 12 is always the first DTC that is displayed when the flash DTC mode is enabled. DTC 12 is not an SIR fault indication. DTC 12 is an indication that the flash DTC mode is enabled. When current DTCs or history DTCs are not present, the SDM displays DTC 12 until you remove the jumper from the Air Bag Diagnostic Connector. Flash DTC 13 displays only if noncurrent history DTCs are present. Use a scan tool for reading history DTCs.