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
The scan tool used provides the following capabilities:
| • | Read the data list |
| • | Read current and history Diagnostic Trouble Codes (DTC) |
| • | Clear the DTCs after a repair is completed |
Make sure the scan tool contains updated software before attempting to communicate with the SIR system. To use the scan tool, connect it to the Data Link Connector (DLC) and turn the ignition switch to the ON position. The scan tool reads serial data sent from the inflatable restraint Sensing and Diagnostic Module (SDM) serial data output terminal 5 to the DLC terminal 9. The following table shows the typical values of the data displays under the following conditions:
| • | Ignition switch in ON |
| • | Engine OFF |
| • | Driver seatbelt buckled |
Data List | Description | Typical Value |
|---|---|---|
Ignition | Ignition 1 power feed | 12 Volts |
Lamp Driver | Warning lamp control method (hard wired lamp) | Internal |
Driver Resistance | Driver deployment loop resistance | 2.6 Ohms |
Passenger Resistance | Passenger deployment loop resistance | 2.2 Ohms |
Driver Senselo | Driver side low terminal voltage | 4.1 Volts |
Passenger Senselo | Passenger side low terminal voltage | 4.1 Volts |
Driver VDIF | Voltage difference between driver side high and driver side low terminals | 4-8 mV |
Passenger VDIF | Voltage difference between passenger side high and passenger side low terminals | 4-8 mV |
Warning Lamp Control | Warning lamp state commanded by the SDM (On/Off) | Off |
Lamp Driver Feedback | Warning lamp state detected by the SDM (Active/Inactive) | Inactive |
Warning Lamp ON | Continuous warning lamp ON time | 0-182 Hrs. |
Warning Lamp Cycles | Ignition cycles of the current warning lamp state. | 0-125 Cycles |
Driver Seatbelt | Driver seatbelt status (Buckled/Unbuckled) | Buckled |
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 |
| • | The J 38715-96 SIR Shorting Bar Tool |
