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Home >> Infiniti >> 1995 >> Q45 Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes 4.5L >> Diagnostic Trouble Code (DTC) Testing >> DTC 21: Ignition Signal
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DTC 21: Ignition Signal

  1. When either cylinders No. 1, 3, 5 and 7 or cylinders No. 2, 4, 6 and 8 are all not operating, go to next step. If there is a different malfunction, go to step 3) or to step 4).
  2. Check Ground Circuit

    Turn ignition off. Disconnect Power Transistor Unit (PTU) harness connectors. Verify harness continuity between PTU harness connector terminals "f" and "l" (Black wire) and engine ground. See Fig 1 -27. If continuity is present, go to step 4). If continuity is not present, repair harness or connectors as necessary and perform FINAL CHECK  .
    Fig 1: Locating Ignition Coil Relay (Q45)
    G93F78589Courtesy of NISSAN MOTOR CO., U.S.A.
    Fig 2: Locating EFI Sub-Harness Connector No. 4 (Q45)
    G94I44147Courtesy of NISSAN MOTOR CO., U.S.A.
    Fig 3: Locating EFI Sub-Harness Connector No. 5 (Q45)
    G94J44148Courtesy of NISSAN MOTOR CO., U.S.A.
    Fig 4: Locating PTU Harness Connector - Left Side (Q45)
    G94A44149Courtesy of NISSAN MOTOR CO., U.S.A.
    Fig 5: Locating PTU Harness Connector - Right Side (Q45)
    G94E44150Courtesy of NISSAN MOTOR CO., U.S.A.
    Fig 6: DTC 21, Checking Ground Circuit (Q45)
    G94F44151Courtesy of NISSAN MOTOR CO., U.S.A.
    Fig 7: Locating Ignition Coils - Right Side (Q45)
    G93D78595Courtesy of NISSAN MOTOR CO., U.S.A.
    Fig 8: Locating Ignition Coils - Left Side (Q45)
    G93E78596Courtesy of NISSAN MOTOR CO., U.S.A.
  3. Search For Malfunctioning Circuit Using CONSULT

    Turn ignition off and connect CONSULT. Perform POWER BALANCE in ACTIVE TEST mode with CONSULT. Search for circuit which does not produce a momentary engine speed drop.
  4. Check Output Signal Circuit

    Turn ignition off. Disconnect ECM harness connector and PTU harness connector. Verify harness continuity between ECM harness connector terminals and PTU harness connector terminals as follows:
    • ECM terminal No. 1 and PTU terminal "e" (Green wire).
    • ECM terminal No. 2 and PTU terminal "f" (Yellow wire).
    • ECM terminal No. 3 and PTU terminal "a" (Green/White wire).
    • ECM terminal No. 11 and PTU terminal "d" (Yellow/White wire).
    • ECM terminal No. 12 and PTU terminal "g" (Green/Black wire).
    • ECM terminal No. 13 and PTU terminal "b" (Yellow/Black wire).
    • ECM terminal No. 14 and PTU terminal "i" (Green/Red wire).
    • ECM terminal No. 15 and PTU terminal "j" (Yellow/Red wire).

    See Fig 9 . If continuity is present, go to next step. If continuity is not present, verify harness continuity between ECM connector and PTU connector. Repair harness or connectors as necessary.

  5. Check Component

    Inspect power transistor unit. See I - SYSTEM/COMPONENT TESTS article. Replace power transistor unit if necessary and perform FINAL CHECK  .
Fig 9: DTC 21, Checking Output Signal Circuit (Q45)
G94J44130Courtesy of NISSAN MOTOR CO., U.S.A.