GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2008 🢒 Corvette 🢒 Engine 🢒 Engine Controls and Fuel - 4.8L, 5.3L, 6.0L, 6.2L, or 7.0L 🢒 Diagnostic System Check - Vehicle

Circuit Description

The ignition mode switch has 2 contact buttons.

The upper button, with a circle indicator on it, that starts the engine if the brake pedal is applied for automatic transmissions, or the clutch pedal is depressed for manual transmissions.

The lower button has 2 indicators on it, O and ACC. This button cycles the ignition through the following modes:

    • OFF
        This is the normal state upon entering the vehicle, and can also be reached from any other mode by depressing the button. The O indicator illuminates.
    • Accessory
        This mode can be reached from the Off state by depressing the button. The ACC indicator illuminates.
    • ON with the engine OFF
        This state can be reached from the Off or Accessory modes by depressing the button for about 5-6 seconds. The upper LED illuminates.

Circuit/System Testing
  1. Before beginning vehicle diagnosis, the following preliminary inspections/tests must be performed:
    2. • Ensure that the battery is fully charged. Refer to Battery Inspection/Test.
    • Ensure that the battery cables are clean and tight.
    • Inspect for any open fuses. Refer to Power Distribution Schematics and Electrical Center Identification Views.
    • Ensure that the grounds are clean, tight, and in the correct location. Refer to Ground Distribution Schematics and Harness Routing Views.
    • Inspect the easily accessible systems or the visible system components for obvious damage or conditions that could cause the concern. This would include checking to ensure that all connections/connectors are fully seated and secured.
    • Inspect for aftermarket devices that could affect the operation of the system. Refer to Checking Aftermarket Accessories.
    • Search for applicable service bulletins.
    ⇒If the preceding inspections/tests resolve the concern, go to Diagnostic Repair Verification.
  2. Ignition ON and engine OFF, verify that the NO FOB DETECTED message is not displayed on the driver information center (DIC).
    3. ⇒If the NO FOB DETECTED message is displayed, refer to Key Fob Not Detected.
  3. Install a scan tool. Verify that the scan tool powers up.
    4. ⇒If the scan tool does not power up, refer to Scan Tool Does Not Power Up.
  4. Ignition ON, Engine OFF, verify communication with all of the control modules on the vehicle. Refer to Data Link References for information on the modules you should expect to communicate.
    5. ⇒If the scan tool does not communicate with one or more of the expected control modules, refer to Data Link References.
  5. Attempt to start the engine. Verify that the engine cranks.
    6. ⇒If the engine does not crank, refer to Symptoms - Engine Electrical.
  6. Attempt to start the engine. Verify the engine starts and idles.
    7. ⇒If the engine does not start and idle, refer to Engine Cranks But Does Not Run.

    Important: 

       • Do not clear any DTCs unless instructed to do so by a diagnostic procedure.
       • If any DTCs are Powertrain related DTCs, select Capture Info in order to store the DTC information with the scan tool.

  7. Advance to the List All DTCs selection on the scan tool. Verify there are no DTCs reported from any module.
    8. ⇒If any DTCs are present, refer to Diagnostic Trouble Code (DTC) List - Vehicle and diagnose any current DTCs in the order they are displayed on the scan tool.
  8. If the customer concern is related to inspection/maintenance (I/M) testing, refer to Inspection/Maintenance (I/M) System Check.
    9. ⇒If none of the previous tests or inspections addresses the concern, refer to Symptoms - Vehicle.