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BASIC DIAGNOSTIC PROCEDURES Chevrolet Chevy Van G30

Ccc Tbi Tests W/codes 1 illustration ~439 words

BASIC DIAGNOSTIC PROCEDURES

Note. Most computerized engine control problems are the result of mechanical breakdowns, poor electrical connections or damaged vacuum hoes. Before considering the computer system as a possible cause of problems ignition high tension wires, fuel supply, electrical connections and vacuum hoses should be checked. Failure to do so may result in lost diagnostic time.

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. Perform appropriate DIAGNOSTIC CIRCUIT CHECK for that system. If trouble codes were displayed (other than Code 12), decide whether codes are "hard" or "intermittent" trouble codes. "Hard" codes will cause the "SERVICE ENGINE SOON" light to illuminate continuously while engine is running. See ECM TROUBLE CODE DEFINITION in this article.
  3. If no trouble codes were displayed, proceed to appropriate SYSTEM PERFORMANCE CHECK chart for carbureted systems or perform FIELD SERVICE MODE CHECK on fuel injected systems.
  4. If no trouble is indicated by SYSTEM PERFORMANCE CHECK or FIELD SERVICE MODE check and/or a driveability problem exists, refer to SYMPTOM DIAGNOSIS and/or SCAN TESTER USAGE TROUBLESHOOTING. The comments there will send you to the proper component charts or tell you the most likely system/component to check.
  5. After any repairs have been made, clear any trouble codes and perform SYSTEM PERFORMANCE CHECK or FIELD SERVICE MODE check.

Scheme 26

Scheme 26: ENTERING OR EXITING DIAGNOSTIC MODE (NON-SCAN)
Scheme 26: ENTERING OR EXITING DIAGNOSTIC MODE (NON-SCAN)
  1. Turn ignition switch on but do not start engine. "SERVICE ENGINE SOON" lamp should glow. Locate Assembly Line Data Link (ALDL) connector attached to ECM wiring harness under instrument panel near steering column (under driver's seat on "G" Series van). Insert jumper wire across terminal "B", "DIAGNOSTIC TERMINAL" and terminal "A", "GROUND". (Scheme 26) CAUTION: Inserting spade lug (jumper lead) into terminals of ALDL connector grounds "DIAGNOSTIC TERMINAL". Do not ground ALDL connector until after ignition is on (engine not running). (Scheme 26): ALDL Connector Terminal Locations NOTE: In some of the diagnostic and trouble shooting charts, the Assembly Line Data Link (ALDL) may also be referred to as the Assembly Line Communication Link (ALCL). These are referring to the same connector. It is also the test point for connection of aftermarket "Scan" testers.
  2. "SERVICE ENGINE SOON" light should flash Code "12". Code "12" consists of "FLASH", pause, "FLASH", "FLASH" followed by a longer pause. Trouble Code "12" will be repeated 2 times. If any trouble codes are stored in ECM memory, they will be displayed in the same manner.
  3. To exit diagnostic mode, turn ignition off and remove jumper wire from ALDL connector.