13A-IGNITION CIRCUIT SYSTEM

Inspection procedure 14: Ignition circuit system

CIRCUIT OPERATION

The 12V starter battery positive voltage is applied from the MFI relay to the ignition coil and is grounded to the vehicle body via the ignition coil.
A power voltage of 5 V is applied to the ignition coil from the ECM terminals CIL1, CIL2, CIL3 and CIL4.

COMMENT

When the ECM turn the power transistor in the unit to OFF, the 12V starter battery positive voltage is applied to the power transistor in the ignition coil, resulting that the power transistor is ON. And, when the ECM 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 ECM, 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.

TROUBLESHOOTING HINTS (The most likely causes for this case:)

Ignition coil failed.
Open or shorted ignition circuit, harness damage or connector damage.
ECM failed.

DIAGNOSIS

Required Special Tool:

MB9919658: Test Harness

STEP 1. Check the ignition coils.

Refer to GROUP 16, Ignition System - On-vehicle Service - Ignition Coil Check

Are there any abnormalities?

Replace the ignition coil. Then confirm that the malfunction symptom is eliminated.

Go to Step 2.

STEP 2. Measure the power supply voltage at ignition coil connectors.

(1) Disconnect the ignition coil connectors and measure at the harness side.

(2) Turn on the power supply mode of the electric motor switch.

(3) Measure the voltage between terminal power supply line and ground.

Voltage should be 12V starter battery positive voltage.

(4) Turn off the power supply mode of the electric motor switch.

Is 12V starter battery positive voltage (approximately 12 volts) present?

Go to Step 3.

Repair or replace the connector(s), or check and repair the harness of short to ground and open circuit in power supply line between MFI relay connector and ignition coil connectors. Then confirm that the malfunction symptom is eliminated.

STEP 3. Measure the output voltage at ignition coil harness side connectors.

(1) Disconnect the ignition coil connectors and connect test harness special tool MB991658 between the separated connector (All terminals should be connected).

(2) Set the vehicle to the continuous idling mode.

(3) Rev the engine with the engine speed of 3,000 r/min.

(4) Measure the voltage between terminal CIL1, CIL2, CIL3, CIL4 and ground.

Voltage should be 0.3 and 3.0 volts.

(5) Turn off the power supply mode of the electric motor switch.

Is the measured voltage between 0.3 and 3.0 volts?

Go to Step 5.

Go to Step 4.

STEP 4. Check of short to ground and open circuit between ignition coil connectors and ECM connector.

Check the harness wire in CIL1 line between ignition coil connector and ECM connector at ignition coil 1.
Check the harness wire in CIL2 line between ignition coil connector and ECM connector at ignition coil 2.
Check the harness wire in CIL3 line between ignition coil connector and ECM connector at ignition coil 3.
Check the harness wire in CIL4 line between ignition coil connector and ECM connector at ignition coil 4.

Is the harness wire in good condition?

Replace the ECM (Refer to Removal and Installation

). Then confirm that the malfunction symptom is eliminated.

Repair it. Then confirm that the malfunction symptom is eliminated.

STEP 5. Check for continuity at ignition coil harness side connectors.

(1) Disconnect the ignition coil connectors and measure at the harness side.

(2) Check for the continuity between terminal ground line and ground.

Continuity (2 ohms or less).

Does continuity exist?

Go to Step 6.

Repair or replace the connector(s), or check and repair the harness of open circuit and harness damage in ground line between ignition coil connectors and ground.

STEP 6. Check of harness damage in power supply line between MFI relay connector and ignition coil connectors.

Is the harness wire in good condition?

Go to Step 7.

Repair the connector(s) or wiring harness. Then confirm that the malfunction symptom is eliminated.

STEP 7. Check of harness damage between ignition coil connectors and ECM connector.

Check the harness wire in CIL1 line between ignition coil connector and ECM connector at ignition coil 1.
Check the harness wire in CIL2 line between ignition coil connector and ECM connector at ignition coil 2.
Check the harness wire in CIL3 line between ignition coil connector and ECM connector at ignition coil 3.
Check the harness wire in CIL4 line between ignition coil connector and ECM connector at ignition coil 4.

Is the harness wire in good condition?

Replace the ECM (Refer to Removal and Installation

). Then confirm that the malfunction symptom is eliminated.

Repair the connector(s) or wiring harness. Then confirm that the malfunction symptom is eliminated.