General Diagnostic Information

CAUTION: When fasteners are removed, always reinstall them at the same location from which they were removed. if a fastener needs to be replaced, use the correct part number fastener for that application. if the correct part number fastener is not available, a fastener of equal size and strength (or stronger) may be used. fasteners that are not reused, and those requiring thread locking compound will be called out. the correct torque value must be used when installing fasteners that require it. if the above conditions are not followed, parts or system damage could result.

WARNING: TO AVOID DEPLOYMENT WHEN TROUBLESHOOTING THE SRS, DO NOT USE ELECTRICAL TEST EQUIPMENT SUCH AS A BATTERY-POWERED OR AC-POWERED VOLTMETER, OHMMETER, ETC., OR ANY TYPE OF ELECTRICAL EQUIPMENT OTHER THAN THAT SPECIFIED IN THIS MANUAL. DO NOT USE A NON POWERED, PROBE-TYPE TESTER. INSTRUCTIONS MUST BE FOLLOWED CAREFULLY, OTHERWISE PERSONAL INJURY MAY RESULT.

The diagnostic procedures used in this section are designed to aid in finding and repairing SRS problems. Outlined below are the steps to find and repair SRS problems quickly and effectively. Failure to carefully follow these procedures may result in extended diagnostic time, incorrect diagnosis and incorrect parts replacement.

1. Perform The "SRS Diagnostic System Check".
The "SRS Diagnostic System Check" SRS Diagnostic System Checkshould always be the starting point of any SRS diagnostics. The "SRS Diagnostic System Check" checks for proper "AIR BAG" warning lamp operation and checks for SRS trouble codes using both "Flash Code" and "Scan Tool" Methods.

2. Refer To The Proper Diagnostic Chart As Directed By The "SRS Diagnostic System Check".
The "SRS Diagnostic System Check" will lead you to the correct chart to diagnose any SRS problems. Bypassing these procedures may result in extended diagnostic time, incorrect diagnosis and incorrect parts replacement.

3. Repeat The "SRS Diagnostic System Check" After Any Repair Or Diagnostic Procedures Have Been Performed.
Preforming the "SRS Diagnostic System Check" after all repair or diagnostic procedures will assure that the repair has been made correctly and that no other conditions exist.

Diagnostic Codes
The Sensing and Diagnostic Module (SDM) maintains a history record of all diagnostic codes that have been detected since the SRS codes were last cleared during service.

1. Active Codes - Faults l:hat are presently detected this ignition cycle. Active codes are stored in RAM (Random Access Memory).
2. History Codes - All faults detected since the last time the history fault memory was cleared. History codes are stored in EEPROM. (Electronically Erasable Programmable Read only Memory)

How To Read Trouble Codes
All codes (Active and history) can be read (or cleared) by using a scan tool or equivalent.
If a PDT is not available, have the vehicle serviced by ISUZU dealer.

How To Clear Trouble Codes
Trouble codes can only be cleared by using a Scan Tool. If a "scan tool" is not available then inform the owner of the stored codes and suggest that the codes are cleared upon the next visit to an Isuzu dealership.


Scan Tool Diagnostics
A scan tool can be used to mad current and history codes and to clear all history codes after a repair is complete. The scan tool must be updated to communicate with the SRS through a replaceable cartridge or a manufacturer's update before it can be used for SRS diagnostics. To use the scan tool, connect it to the DLC connector and turn the ignition switch "ON". Then follow the manufacturer's directions for communication with the SRS. The scan tool reads serial data from the SDM "Serial Data" output (terminal 24) to the DLC connector (terminal 9).


Basic Knowledge Required
Before using this section of the Service Manual, there is some basic knowledge which will be required. Without this knowledge, you will have trouble using the diagnostic procedures in this section. Use care to prevent harm or unwanted deployment. Read all cautions in the service manual and on warning labels attached to SRS components.


Basic Electrical Circuits
You should understand the basic theory of electricity including series and parallel circuits, and understand the voltage drops across series resistors. You should know the meaning of voltage (volts), current (amps), and resistance (ohms). You should understand what happens in a circuit with an open or a shorted wire. You should be able to read and understand a wiring diagram.

SRS System Schematic:

"Flash Code" Diagnostics
Flash code diagnostics can be used to read active codes and to determine if history codes are present but cannot be used to clear codes or read history codes. Flash code diagnostics is enabled by grounding by terminal 4 shorting to terminal 13 of the DLC connector with the ignition switch "ON". Grounding terminal 4 of the DLC connector pulls the "Diagnostics Request" input (Terminal 1) of the SDM low and signals the SDM to enter the flash code diagnostic display mode.