Inspection Procedure 24: Ignition Circuit System

OPERATION

The battery voltage is applied from the engine control relay connector terminal to the ignition coil connector terminal and is earthed to the vehicle body via the ignition coil connector terminal.
A power voltage of 12 V is applied to the ignition coil connector terminal from the engine-ECU connector terminals CIL1, CIL2, CIL3 and CIL4.

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. Visual check of ignition spark.

Remove the spark plug and install it to the ignition coil.
Connect the ignition coil connector.
Disconnect all injector connectors.
At the engine start, check each spark plug produces a spark.

Q. Is the check result normal?

	Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).

	Go to Step 2.

STEP 2. Check spark plug.

Check spark plug (Refer to GROUP 16 - Ignition System - On-vehicle Service - Spark Plug Check and Cleaning ).

Q. Is the check result normal?

	Go to Step 3.

	Replace the spark plug.

STEP 3. Check ignition coil itself.

Ignition coil connector check.
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 4.

	Repair or replace the connector, or replace the ignition coil.

STEP 4. Perform voltage measurement at No. 1, No. 2, No. 3 and No.4 ignition coil connectors.

Disconnect connector, and measure at harness side.
Ignition switch: ON
Voltage between terminal power supply line and body earth.

OK: System voltage

Q. Are the check results normal?

	Go to Step 5.

	Repair or replace the connector, or check and repair harness between engine control relay connector terminal and No. 1, No. 2, No. 3 and No. 4 ignition coil connector terminals. Check power supply line for open/short circuit.

STEP 5. Perform resistance measurement at No. 1, No. 2, No. 3 and No.4 ignition coil connectors.

Disconnect connector, and measure at harness side.
Resistance between terminal earth line and body earth.

OK: Continuity (2 Ω or less)

Q. Are the check results normal?

	Go to Step 6.

	Repair or replace the connector, or check and repair harness between No. 1, No. 2, No. 3 and No. 4 ignition coil connector terminals and body earth. Check earthing line for open circuit and damage.

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

Check and repair harness between No. 1 ignition coil connector terminal and engine-ECU connector terminal CIL1
Check and repair harness between No. 2 ignition coil connector terminal and engine-ECU connector terminal CIL2
Check and repair harness between No. 3 ignition coil connector terminal and engine-ECU connector terminal CIL3
Check and repair harness between No. 4 ignition coil connector terminal and engine-ECU connector terminal CIL4

Check signal line for open/short circuit and damage.

Q. Are the check results normal?

	Go to Step 7.

	Repair or replace the connector, or repair the damaged harness wire.

STEP 7. Check harness between engine control relay connector terminal and No. 1, No. 2, No. 3 and No.4 ignition coil connector terminals.

Check power supply line for damage.

Q. Are the check results normal?

	Go to Step 8.

	Repair or replace the connector, or repair the damaged harness wire.

STEP 8. 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 ).