Diagnostic Procedure
Diagnosis of computerized engine control system should be performed in following order:
- Ensure all engine systems not related to computer system are operating properly. DO NOT proceed with testing unless all other problems have been repaired. DIAGNOSTIC CIRCUIT CHECK must be performed before using trouble code charts. See BASIC TESTING article in this section.
- If trouble codes were displayed (other than Code 12), determine whether codes are hard or intermittent trouble codes. Hard codes will cause SERVICE ENGINE SOON light to glow continuously while engine is running. See HARD OR INTERMITTENT TROUBLE CODE DETERMINATION . For diagnosing hard codes, proceed to appropriate trouble code chart. For diagnosing intermittent codes, proceed to INTERMITTENTS in TESTS W/O CODES article in this section. Exceptions are Code 13, 15, 24, 44 and 45 charts, which may be used to help diagnose intermittent codes.
- If no trouble codes were displayed and a driveability problem exists, refer to SYMPTOMS in TESTS W/O CODES article in this section. Doing so will identify proper system or component to check in appropriate I - SYS/COMP TESTS article in this section.
- After repairs are made, clear any trouble codes and perform FIELD SERVICE MODE CHECK in BASIC TESTING
article in this section.NOTE: For information on retrieving codes using a "Scan" tester, refer to user and reference manuals supplied with tester.NOTE: Inserting jumper wire into test and ground terminals of ALDL connector with engine running will cause fuel injected vehicles to enter field service mode. Flashes of SERVICE ENGINE SOON light will not indicate codes if this is done. See FIELD SERVICE MODE CHECK in BASIC TESTING article in this section.
- Turn ignition on. DO NOT start engine. SERVICE ENGINE SOON light should glow. Locate Assembly Line Data Link (ALDL) connector attached to control module wiring harness. Most ALDL connectors are located under dash on driver side of vehicle. For exact location of ALDL, see COMPONENT LOCATIONS in appropriate I - SYS/COMP TESTS article in this section. Insert jumper wire from terminal "B" (diagnostic test terminal) to terminal "A" (ground) of ALDL connector. See Fig 1 .
- SERVICE ENGINE SOON light should begin to flash codes. Each code will be repeated 3 times. If codes are not flashed or SERVICE ENGINE SOON light does not glow, perform DIAGNOSTIC CIRCUIT CHECK in BASIC TESTING article in this section. To exit diagnostic mode, turn ignition off and remove jumper wire from ALDL connector.