Inspection Procedure 22: Ignition Circuit System










OPERATION



  • The battery voltage is applied from the engine control relay to the ignition coil (terminal No.3) and is earthed to the vehicle body via the ignition coil (terminal No.1).
  • A power voltage of 12 V is applied to the ignition coil (terminal No. 3) from the engine-ECU (terminal No. 4, No. 5, No. 20 and No. 21).

FUNCTION



  • When the engine-ECU turn the power transistor in the unit to OFF, the battery voltage is applied to the power transistor in the ignition coil, resulting that the power transistor is ON.And, when the engine-ECU turns the power transistor in the unit to ON, the power transistor in the ignition coil will be turned OFF.
  • When the power transistor in the ignition coil is turned to ON with any signal from the engine-ECU, the primary voltage will be applied through the ignition coil.When the power transistor in the ignition coil is turned OFF, the primary current is blocked and high voltage is generated in the secondary coil.

PROBABLE CAUSES



  • Failed spark plug
  • Failed ignition coil
  • Open/short circuit or harness damage in ignition system circuit or loose connector contact
  • Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Connector check: B-24, B-25, B-26 and B-27 ignition coil connectors

Q. Are the check results normal?
Go to Step 2 .
Repair or replace the connector.

STEP 2. Check ignition coil itself.

  • Check ignition coil itself (Refer to GROUP 16 - Ignition System - On-vehicle Service - Ignition Coil Check ).

Q. Is the check result normal?
Go to Step 3 .
Replace the ignition coil.

STEP 3. Perform voltage measurement at B-24, B-25, B-26 and B-27 ignition coil connectors.

  • Disconnect connector and measure at harness side.
  • Ignition switch: ON
  • Voltage between terminal No. 3 and earth.
OK: System voltage

Q. Are the check results normal?
Go to Step 5 .
Go to Step 4 .

STEP 4. Connector check: A-33X engine control relay connector

Q. Is the check result normal?

    Check intermediate connector A-13, and repair if necessary.If intermediate connector is normal, check and repair harness between A-33X (terminal No. 2) engine control relay connector and B-24, B-25, B-26, and B-27 (terminal No. 3) ignition coil connectors.

    • Check power supply line for open/short circuit.
Repair or replace the connector.

STEP 5. Perform resistance measurement at B-24, B-25, B-26 and B-27 ignition coil connectors.

  • Disconnect connector and measure at harness side.
  • Resistance between terminal No. 1 and earth.
OK: Continuity (2 Ω or less)

Q. Are the check results normal?
Go to Step 6 .

    Check and repair harness between B-24, B-25, B-26 and B-27 (terminal No. 1) ignition coil connectors and body earth.

    • Check earthing line for open circuit and damage.

STEP 6. Check harness between ignition coil connector and engine-ECU connector.

  1. Check and repair harness between B-24 (terminal No.2) ignition coil connector and B-29 (terminal No.4) engine-ECU connector
  2. Check and repair harness between B-25 (terminal No.2) ignition coil connector and B-29 (terminal No.5) engine-ECU connector
  3. Check and repair harness between B-26 (terminal No.2) ignition coil connector and B-29 (terminal No.20) engine-ECU connector
  4. Check and repair harness between B-27 (terminal No.2) ignition coil connector and B-29 (terminal No.21) engine-ECU connector

  • Check signal line for open/short circuit and damage.

Q. Are the check results normal?
Go to Step 7 .
Repair the damaged harness wire.

STEP 7. Check harness between A-33X (terminal No. 2) engine control relay connector and B-24, B-25, B-26, and B-27 (terminal No. 3) ignition coil connectors.
note Before checking harness, check intermediate connector A-13, and repair if necessary.

  • Check power supply line for damage.

Q. Are the check results normal?
Go to Step 8 .
Repair the damaged harness wire.

STEP 8. Check ignition coil spark.

  • Check whether the spark plug connected to each ignition coil can spark at engine cranking.

Q. Is the check result normal?
Replace the spark plug.
Go to Step 9 .

STEP 9. Check the trouble symptom.

Q. Does the trouble symptom persist?
Replace the engine-ECU.
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).