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BASIC DIAGNOSTIC PROCEDURE - TESTING GMC S15 Pickup

2.5l Tbi Tests W/codes 1 illustration ~369 words

BASIC DIAGNOSTIC PROCEDURE - TESTING

Diagnosis of the CCC system should be performed in the following order

  1. Make sure that all engine systems not related to the CCC system are operating properly. Do not proceed with testing unless all other problems have been repaired.
  2. Go to the Diagnostic Circuit Check chart and follow all instructions given there to verify proper operation of ECM self-diagnostics and to obtain any stored trouble codes.
  3. If trouble codes were displayed, determine whether the codes are "intermittent" or "hard". Go to numbered Code Charts for further diagnosis of stored trouble codes.
  4. If no trouble codes were displayed, proceed to Field Service Mode on TBI models (part of Diagnostic Circuit Check).
  5. If no trouble is indicated by any of these charts, use the TROUBLE SHOOTING material in this article. The comments there will send you to the proper component charts or tell you what to fix.
  6. After any repairs have been made, always perform System Performance Check. Clear any trouble codes.

Note. Each of the steps listed here are described later in this section. If you are unsure of the proper way to test, read through the following material.

Scheme 64

Scheme 64: ENTERING OR EXITING DIAGNOSTIC MODE
Scheme 64: ENTERING OR EXITING DIAGNOSTIC MODE
  1. Turn ignition switch on but do not start engine. "SERVICE ENGINE SOON" lamp should glow. Locate Assembly Line Communication Link (ALCL) connector attached to ECM wiring harness under instrument panel near the steering column (under driver's seat on "G" model vans). Insert spade lug terminal across the "TEST" terminal and "GROUND" terminal. (Scheme 64) CAUTION: Inserting spade lug in terminals of ALCL connector grounds "TEST" terminal lead. Do not ground ALCL connector until after ignition is on or engine is started. (Scheme 64): ALCL Connector Terminal Locations
  2. "SERVICE ENGINE SOON" light should flash code "12" ("FLASH", pause, "FLASH", "FLASH"). Code "12" will be repeated 3 times. If any trouble codes are stored in the ECM memory, they will be displayed in the same manner.
  3. Trouble codes will be displayed from lowest to highest numbered codes (3 times each) and be repeated as long as the "TEST" terminal of the ALCL connector is grounded.
  4. To exit diagnostic mode, turn ignition switch off and remove spade lug terminal from ALCL connector.