Accessing and Reading Diagnostic Trouble Codes

DIAGNOSTIC TROUBLE CODES (DTC)

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 using the scan tool.

1. Current diagnostic trouble codes - Malfunctions that are presently being detected. Current diagnostic trouble codes are stored in RAM (Random Access Memory).

2. History diagnostic trouble codes - All malfunctions detected since the last time the history memory was cleared. History diagnostic trouble codes are stored in EEPROM.

Scan Tool Diagnostics

A scan tool is used to read current and history diagnostic trouble codes and to clear all diagnostic trouble codes after a repair is completed. The scan tool must be updated to communicate with the SIR system through a replaceable cartridge before it can be used for SIR diagnostics. To use the scan tool, connect it to the data link connector and turn the ignition switch to "ON." The scan tool reads serial data from the SDM "Serial Data" output terminal "1" to the data link connector terminal "9."

Flash DTC Diagnostics

Flash DTC diagnostics can only be used to read current DTCs and to determine when history DTCs are present. Flash DTC diagnostics cannot be used to clear DTCs or read history DTCs. Flash DTC diagnostics is enabled by jumping the Air Bag Diagnostic Connector terminals with the ignition switch to "ON." Jumping the Air Bag Diagnostic Connector terminals 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 flashes which represent the tens, or first DTC digit; then a 1/2 second pause, followed by flashes which represent the ones, or second DTC digit. Each DTC is flashed once before moving on to the next DTC. After all DTCs have been displayed, the entire DTC sequence is continually repeated until the jumper is removed 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, but an indication that the flash DTC mode is enabled. When there are no current or history DTCs present, the SDM displays DTC 12 until the jumper is removed from the Air Bag Diagnostic Connector. Flash DTC 13 displays only if there are history DTCs that are not current. To read history DTCs a scan tool must be used.