LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> GMC >> 1995 >> Forward Control 4.3 Z, Automatic >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Controls - Tests W/Codes - 6.5L Diesel. >> Self-Diagnostic System >> Entering & Exiting Diagnostic Mode
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Entering & Exiting Diagnostic Mode

  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 (D EC)/electronically-controlled transmission systems will enter diagnostic mode.
  2. In this mode, PCM/TCM 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.
Fig 1: Identifying DLC Terminals (All Models)
G95A26930Courtesy of GENERAL MOTORS CORP.
scientia non olet · About LEMON Manuals