Diagnostic Trouble Codes
CAUTION: In order to avoid deploying the air bag when troubleshooting the SRS 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 SRS system repairs.
Begin all SRS diagnosis with the SRS Diagnostic System Check. Performing the SRS Diagnostic System Check determines the operational status of the SRS by checking the following functions:
| • | Operation of the AIR BAG warning lamp |
| • | Communication with the scan tool through the serial data line |
| • | The presence of diagnostic trouble codes (current or history) |
Current diagnostic trouble codes indicate malfunctions occurring right now. The presence of a current DTC causes illumination of the AIR BAG warning lamp. Current diagnostic trouble codes are stored in Random Access Memory (RAM). Turning the ignition switch off erases current diagnostic trouble codes.
History diagnostic trouble codes indicate malfunctions which have occurred since the last time DTCs were cleared but are not presently being detected. The presence of a history DTC does not cause illumination of the AIR BAG warning lamp. History diagnostic trouble codes are stored in the Electrically Erasable Programmable Read-Only Memory (EEPROM). Scan tool clear code's command will erase history diagnostic trouble codes.
Scan Tool Diagnostics
You must use a scan tool to read and clear the Supplemental Restraint System (SRS) DTCs. The scan tool may need to be updated to communicate with the SRS before it can be used for SRS diagnostics. In order to use the scan tool, connect it to the data link connector and turn ON the ignition switch. The scan tool reads serial data from the DERM serial data output terminal B11 at the data link connector terminal 9. A scan tool can also provide SRS circuit values are refered to in the diagnostic trouble code tables to aid in diagnosing certain SRS malfunctions. For additional information, refer to the scan tool instruction manual. After completing a repair, use the scan tool to clear the DTC(s) and then perform the SRS Diagnostic System Check. The following table shows the typical scan tool values under the fgollowing conditions:
| • | Ignition switch to RUN |
| • | Engine OFF |
| • | Driver seatbelt buckled |
Data List | Description | Typical Value |
|---|---|---|
Ignition | Ignition 1 power feed | 12 V |
Driver Resistance | Driver deployment loop resistance | 2.8 ohms * 3.3 ohms ** |
Driver Senselo | Driver side low terminal voltage | 15.8 V |
Driver VDIF | Voltage difference between driver side high and driver side low terminals | 0-16 mV |
Driver Source | Output voltage available at Derm for deployment | 33-36 V |
Driver 36 VLR | Deployment energy supply from Derm | 34-36 V |
Discriminating Sensor | State of switch in discriminating sensor (Open/Closed) | Open |
Arming Sensor | State of switch in arming sensor (Open/Closed) | Open |
Coil Resistance | Calculated resistance of steering wheel coil | 0.5 ohms * 1.0 ohms ** |
1st Lamp Driver | State of 1st warning lamp driver (On/Off) | Off |
2nd Lamp Driver | State of 2nd warning lamp driver (On/Off) | Off |
Warning Lamp feedback | Warning lamp state detected by the Derm (On/Off) | Off |
Driver Seatbelt Monitor | (Enabled/Disabled) | Enabled |
Driver Seatbelt | Driver seatbelt status (Buckled/Unbuckled) | Buckled |
Backup Warning | Monitors lamp drivers functionality. (Active) When lamp driver is not functional. (Inactive) When lamp driver is functional | Internal |
Crank | Cranking signal input to Derm (Yes/No) | No |
Serial Data Telltale | Warning lamp control method. (Internal) Hard wired lamp. (External) Serial data controled lamp. | Inactive |
Deploy Command | Status of command to deploy air bag (Active/Inactive) | Inactive |
Derm Type | Derm configuration (Driver only/Driver passenger) | Driver only |
Rom ID | Software revision level in Derm | Revision # |
* When Driver Resistance is 2.8 ohms Coil Resistance will be 0.5 ohms. ** When Driver Resistance is 3.3 ohms Coil Resistance will be 1.0 ohms. | ||
Use of Special Tools
CAUTION: In order to avoid deploying the air bag when troubleshooting the SRS 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 SRS system repairs.
You should be familiar with the tools in this service category listed under the heading SRS Special Tools. You should know how to measure voltage and resistance. You should be familiar with the proper use of the following tools:
| • | Scan Tool Tech 2 Scan Tool |
| • | J 38715-A SRS Driver/Passenger Load Tool |
| • | J 35616 Connector Test Adapter Kit |
| • | J 39200 Digital Multimeter |
