Diagnostic Trouble Codes
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 checks for proper AIR BAG warning lamp operation and checks for SIR Diagnostic Trouble Codes (DTC) using the scan tool. The following describes the difference between current 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 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. |
Some DTCs are latched and can not be cleared. Latched DTCs will require replacement of the SDM after proper diagnostics.
Scan Tool Diagnostics
A scan tool is used in order to read data lists, current and history diagnostic trouble codes. The tool is also used in order to clear all diagnostic trouble codes after a repair is completed. Make sure the scan tool contains updated software before attempting to communicate with the SIR system. Connect the tool to the 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 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 current DTCs and determine when history DTCs are present. Flash DTC diagnostics do not clear DTCs or read history DTCs. You can enable flash DTC diagnostics by jumping the Air Bag Diagnostic Connector terminals 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. Each DTC that is displayed consists of the following:
- A series of flashes which represent the tens (first) DTC digit
- A half-second pause
- A series of flashes which represent the ones (second) DTC digit
Each DTC is flashed once before moving on to the next DTC. After the tool displays all DTCs, the entire DTC sequence is continually 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 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 no current or history DTCs are 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.
Use of Special Tools
You should be familiar with the tools in this service category listed under the heading Special Tools. You should know how to measure voltage and resistance. Diagnosis requires proper use of the following tools:
| • | The Scan Tool |
| • | The J 38715-A SIR Driver/Passenger Load Tool |
| • | The J 35616 Connector Test Adapter Kit |
| • | The J 39200 Digital Multimeter (DMM) |
| • | The J 38715-96 SIR Shorting Bar Tool |
