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Electronic Ignition (EI) System Diagnosis with LY7

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    •  Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description

The ignition system on this engine uses individual ignition coils and ignition control (IC) circuits for each cylinder. Ignition voltage is supplied to each bank of ignition coils. The engine control module (ECM) controls the ignition system operation. The ECM controls each coil using the IC circuits. The ECM commands the IC circuit low when a spark event is requested. The sequencing and timing are controlled by the ECM.

Diagnostic Aids
    • The ignition coils for each bank are fused separately. If a fuse opens or the ignition voltage circuit opens between the fuse and the splice, all the ignition coils for one bank of the engine would be inoperative. If the ground circuit opens at the engine block, the ignition coils would be inoperative for one bank of the engine.
    • Inspect the ignition coils for aftermarket devices. An aftermarket device connected to the ignition coil circuits, may cause a condition with the ignition coils.

Reference Information

Schematic Reference

Engine Controls Schematics

Description and Operation

Electronic Ignition (EI) System Description

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Special Tools

    • J 26792 Spark Tester
    • J 43244 Relay Puller Pliers

Circuit/System Testing

    Note: Do not perform this diagnostic procedure if you were not sent here from a misfire DTC or the Engine Cranks but Does Not Run diagnostic.

  1. Ignition OFF, disconnect the harness connector of the ignition coil.
  2. Ignition ON, load test for battery voltage between the ignition voltage circuit terminal D and ground.
    3. ⇒If less than B+, test the ignition voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test all the components connected to the ignition voltage circuit and replace as necessary.
  3. Crank or start the engine. Test for 200-400 mV between the appropriate IC circuit terminal C and ground.
    4. ⇒If less than the specified value, test the IC circuit for a short to ground or an open/high resistance. If the circuit/connection tests normal, replace the ECM.
    ⇒If greater than the specified value, test the IC circuit for a short to voltage. If the circuit/connection tests normal, replace the ECM.
  4. Ignition OFF, connect a test lamp between the low reference circuit terminal B and B+. The test lamp should illuminate.
    5. ⇒If the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuit/connection tests normal, replace the ECM.
  5. Connect a test lamp between the ground circuit terminal A and B+. The test lamp should illuminate.
    6. ⇒If the test lamp does not illuminate, test the circuit for an open/high resistance.
  6. If all circuits/connections test normal, replace the ignition coil.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Ignition Coil Replacement - Bank 1
    •  Ignition Coil Replacement - Bank 2