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Home >> GMC >> 1993 >> Magnavan 7.4 N >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes - Diesel >> Self-Diagnostic System >> Entering Or Exiting Diagnostic Mode
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Entering Or Exiting Diagnostic Mode

NOTE: The Assembly Line Data Link (ALDL) connector is also referred to as the Data Link Connector (DLC). This is the same connector.
  1. With ignition on and engine off, connect a jumper wire between Data Link Connector (DLC) terminal "B" (diagnostic terminal) and terminal "A" (ground). See Fig 1. The Diesel Electronic Control (DEC) system will enter diagnostic mode.
  2. In this mode, ECM will display DTC 12 by flashing the MIL once, followed by a short pause, then 2 flashes in quick succession.
  3. DTC 12 will be displayed 3 times. If no other codes are stored, DTC 12 will continue to flash until diagnostic terminal is ungrounded. To exit diagnostic mode, turn ignition off and remove jumper from DLC connector.
Fig 1: Identifying DLC Connector Terminals
G120880Courtesy of GENERAL MOTORS CORP.
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