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Test D11 - Check Engine

NOTE: To prevent replacement of good components, be aware that the following non-EEC related areas may be at fault: fuses, bulb, or socket. This circuit test checks STO-MIL circuit and ECA. You should perform this test when Codes 70, 71 or 72 is displayed, or when directed here by other test procedure.
Fig 1: "CHECK ENGINE" Light (Malfunction Indicator) Circuit
G120762
NOTE: All service codes, except a Code 11 (pass), must be cleared before continuing.
  1. "CHECK ENGINE" Light Always On: Checking For Short to Ground. If vehicle will not start, go to TEST A1 - NO START  , step 1). Turn key off. Disconnect ECA 60-pin connector. Inspect connector and wires for damage, corrosion, or loose wires and repair as necessary. Install breakout box, leaving ECA disconnected. Set DVOM on 200K-ohm scale. Connect DVOM between test pins No. 17 and No. 40 at the breakout box. If resistance is greater than 10K ohms, replace ECA. If reading is less than 10K ohms, repair short between test pin No. 17 and SELF-TEST connector or "CHECK ENGINE" light.
  2. "CHECK ENGINE" Light Never On: Check Continuity of STO/MIL Circuit. If vehicle will not start, go to TEST A1 - NO START  , step 1). Turn key off. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, or loose wires. Repair if necessary. Install breakout box, leaving ECA disconnected. Set DVOM on 200-ohm scale. Measure resistance between test pin No. 17 and "CHECK ENGINE" light. If resistance is less than 5 ohms, go to next step. If not, repair open circuit in wiring harness and rerun QUICK TEST.
  3. Checking For Power to "CHECK ENGINE" Light Bulb. If power exists at bulb, replace bulb or socket and go to next step. If no power exists at socket, check fuse and input circuit, and then go to next step.
  4. Confirming Circuit Repair. Remove breakout box and reconnect ECA to harness. Turn key to "RUN" position. See if "CHECK ENGINE" light is on. If light is on, malfunction indicator system is okay. If light does not come on, replace ECA.
  5. "CHECK ENGINE" Light Intermittently ON: Check For Short From STO to Ground. If vehicle does not start, go to TEST A1 - NO START  , step 1). Service all Continuous Memory Codes before proceeding. If no codes are outputted, proceed with this test. Enter KOEO CONTINUOUS MONITOR MODE ("WIGGLE TEST"). Observe DVOM for indication of fault while performing "Wiggle" test on the harness in the following areas.
    • From Self-Test connector to dash panel.
    • Dash panel to ECA.
    • Dash panel to "CHECK ENGINE" light.

    If a fault is indicated, repair as necessary and rerun QUICK TEST. If a fault is not indicated, fault cannot be duplicated at this time.

  6. "CHECK ENGINE" Light Flashes With Erratic Idle: Check STI Short to Ground. Vehicle symptoms indicate STI is grounded and ECA is performing Self-Test without tester installed. With key off, disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, or loose wires. Repair if necessary. Set DVOM on 200K-ohm scale. Measure resistance between STI connector and engine block ground. If resistance is less than 10K ohms, repair short circuit. Reconnect ECA and retest. If reconnect ECA and test for other rough idle symptoms.
  7. "CHECK ENGINE" Message Displayed. If vehicle will not start, go to TEST A1 - NO START  , step 1). Perform KOEO SELF-TEST, if the result is a pass code (11-10-11), repair fault in electronic message center Data Communications Link (DCL). If Pass Code is not displayed, service codes as described in Self-Test procedures.
  8. Continuous Memory Code 70, 71 and 72: "CHECK ENGINE" Light On. Codes 70, 71 and 72 indicate a circuit failure has occurred on the Data Communications Link (DCL). These codes can occur alone or together. "CHECK ENGINE" message will be on.
    • Code 70 indicates ECA is unable to transmit data.
    • Code 71 indicates Cluster Control Assembly (CCA) is unable to transmit data.
    • Code 72 indicates that Message Center Control Assembly (MCCA) is unable to transmit data.

    Perform KOEO SELF-TEST, if the result is a Pass Code (11-10-11), repair fault in electronic message center Data Communications Link (DCL). If pass code is not displayed, service codes as described in Self-Test procedures.

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