General Diagnostic Information
DIAGNOSTIC PROCEDURESWARNING: 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 IN THIS MANUAL 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" should 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.
Performing 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 that 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 a ISUZU dealership.
SCAN TOOL DIAGNOSTICS
A Scan Tool can be used to read 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 A11) to the DLC connector (terminal M).
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 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.
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 A12) of the SDM low and signals the SDM to enter the flash code diagnostic display mode.
The SDM displays the trouble codes by flashing the warning lamp. Each code that is displayed will consist of a number of flashes which represents the tens digit, a 1.2 second pause, following by a number of flashes which represents the ones digit of the code. Each code is displayed one time before moving on to the next code. After all of the codes have been displayed, the entire code sequence will continually by repeated until ground is removed from terminal 4 of the DLC connector.
Two special codes exist when reading in the flash code mode (Flash Code 12 and Flash Code 13). "Flash Code 12" will always be the first code displayed when the flash code mode is enable Code 12 is not an indication of a SRS problem but an indication that the flash code mode has been enabled. If there are no active or history codes present, the SDM will display code 12 until ground is removed from the DLC connector at terminal 4. "flash Code 13" will be displayed if history codes are present. To read the history codes a scan tool must be used.