Test DTC - Checking System For Diagnostic Trouble Codes

NOTE: Ensure battery is fully charged before proceeding with test.

Attempt to start engine. Crank engine for up to 10 seconds (if necessary). Diagnostic Trouble Codes (DTCs) may be retrieved using scan tool or Malfunction Indicator Light (MIL) on instrument panel.
If using MIL on instrument panel to check for DTCs, see RETRIEVING DIAGNOSTIC TROUBLE CODES for proper procedure. Read DTC code flashed by the MIL.
If using scan tool to check for DTCs, connect scan tool to Data Link Connector (DLC). For Data Link Connector (DLC) location, See Figure. Using scan tool manufacturer's instructions, read DTC message and code.
If scan tool displays NO RESPONSE, go to TEST NS-6A. If scan tool will not power up, check for loose cable connections or bad cable. If cable connections and cable are okay, check voltage at cavity No. 16 (Pink wire) on DLC. Voltage should be at least 11 volts. If voltage is not as specified, check wiring circuit and necessary fuses. See the WIRING DIAGRAMS - NON-TURBO article.
If scan tool displays an error message, (i.e. USER-REQUESTED COLD BOOT or USER-REQUESTED WARM BOOT), follow scan tool instructions. If scan tool displays a BUS failure (i.e. SHORT TO BATTERY), this indicates either scan tool failure or BUS failure. To diagnose and correct BUS failures, see VEHICLE COMMUNICATIONS article in the ACCESSORIES/SAFETY EQUIPMENT section.
If DTCs are displayed, see DTC MESSAGES & CODES table and perform appropriate test(s). If no DTCs are displayed, refer to one of the following:
- For Driveability problems, perform TEST NTC-1A.
- For No-Start problems, perform TEST NS-1A.
- For Speed (Cruise) Control problems, perform TEST TC-15A. See the CRUISE CONTROL SYSTEMS article in the ACCESSORIES/SAFETY EQUIPMENT section.
- For Charging system problems, perform TEST TC-5A. See the GENERATORS & REGULATORS article in the ELECTRICAL section.

NOTE: Some Diagnostic Trouble Codes (DTCs) have more than one meaning. Malfunction Indicator Light (MIL) is unable to distinguish between different failures. As an example, there are 4 different failures possible for the oxygen sensor (O2S) system, MIL can only identify an O2S failure by flashing a DTC 21. MIL is capable of displaying all possible system failures.

NOTE: A scan tool may not be able to identify all possible Diagnostic Trouble Codes (DTCs). As an example, a scan tool may not be able to identify or display a DTC for a malfunctioning A/C clutch relay circuit. There are 21 DTCs which a scan tool cannot identify. The Malfunction Indicator Light (MIL) must be used to identify these malfunctions.