Set Timing Mode

The set timing mode is used to tell the ECM to control the spark timing to the ten degree BTDC base timing setting, to permit verification and setting of spark timing. The ECM has a SET TIMING request line that goes to the ALDL connector terminal B. Set Timing mode is requested as follows:

1. Start engine, allow to idle until coolant temperature reaches 85 degrees centigrade. Use the ENGINE DATA options on the CCDIC to verify coolant temperature.
2. Verify that engine is idling less than 900 RPM.
3. Make sure that the transmission is in PARK.
4. If in diagnostics, exit diagnostics by pressing reset on the CCDIC until the CCDIC is back in the standard climate control mode.
5. Jumper pin B of the ALDL to ALDL pin A (ground). See Fig 1 and Fig 2 .
   • The ECM will command the BCM to display a message "SET TIMING" on the CCDIC;
   • Engine will operate at base timing.

     Timing can now be checked with a standard timing light - it should be set to 10 Degrees BTDC.

   Fig 1: Locating ALDL

   Courtesy of GENERAL MOTORS CORP.
   Fig 2: Identifying ALDL Terminals

   Courtesy of GENERAL MOTORS CORP.
6. To exit SET TIMING mode, remove the ground from pin B of the ALDL connector and verify proper display operation.