Inspection Procedure 39: Ignition Circuit System <135>

OPERATION

The battery voltage is applied to the ignition coil (terminal No. 1) from the ignition switch and is earthed to the vehicle body from the ignition coil (terminal No. 2).
A power voltage of 12 V is applied to the ignition coil output terminal (terminal No. 3) from the engine-ECU or engine-A-M/T-ECU (terminal No. 10, No. 25, No. 40 and No. 55).

FUNCTION

When the engine-ECU or engine-A-M/T-ECU makes the power transistor in the unit be in "OFF" position, the battery voltage in the unit is applied to the power transistor unit, and that makes the power transistor unit be in "ON" position. The engine-ECU or engine-A-M/T-ECU makes the power transistor in the unit be in "ON", and that makes the power transistor unit be in "OFF" position.
In response to the signal from the engine-ECU or engine-A-M/T-ECU, the power transistor unit is in "ON" position. The primary current is going to the ignition coil. When the power transistor unit is in "OFF" position, the primary current is interrupted and high voltage is generated in the secondary coil.

PROBABLE CAUSES

Failed ignition coil
Failed spark plug
Open or shorted ignition primary circuit, harness damage, or connector damage
Failed engine-ECU or engine-A-M/T-ECU

DIAGNOSIS PROCEDURE

STEP 1. Check spark plug.

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

Q. Is the check result normal?

	Go to Step 2 .

	Replace spark plug.

STEP 2. Connector check: A-103, A-104, A-105 and A-106 ignition coil connectors

Q. Is the check result normal?

Go to Step 3 .

Repair or replace the connector.

STEP 3. 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 4 .

	Replace the ignition coil.

STEP 4. Perform voltage measurement at A-103, A-104, A-105 and A-106 ignition coil connectors.

Disconnect connector, and measure at harness side.
Ignition switch: ON
Voltage between terminal No. 1 and earth.

OK: System voltage

Q. Is the check result normal?

Go to Step 6 .

Go to Step 5 .

STEP 5. Connector check: B-240 ignition switch connector

Q. Is the check result normal?

Check and repair harness between B-240 (terminal No. 2) ignition switch connector and A-103 (terminal No. 1) No. 1 ignition coil connector
Check and repair harness between B-240 (terminal No. 2) ignition switch connector and A-104 (terminal No. 1) No. 2 ignition coil connector
Check and repair harness between B-240 (terminal No. 2) ignition switch connector and A-105 (terminal No. 1) No. 3 ignition coil connector
Check and repair harness between B-240 (terminal No. 2) ignition switch connector and A-106 (terminal No. 1) No. 4 ignition coil connector

Check power supply line for open/short circuit.

Repair or replace the connector.

STEP 6. Perform voltage measurement at A-103, A-104, A-105 and A-106 ignition coil connectors.

Disconnect connector, and measure at harness side.
Engine: Cranking
Voltage between terminal No. 3 and earth.

OK: 0.5 - 4.0 V

Q. Is the check result normal?

Go to Step 12 .

Go to Step 7 .

STEP 7. Perform voltage measurement at A-08 engine-ECU connector or engine-A-M/T-ECU connector.

Disconnect the engine-ECU connector or engine-A-M/T-ECU connector, and connect special tool power plant ECU check harness (MB991987), and then measure the voltage on the check connector.
Disconnect A-103, A-104, A-105 and A-106 ignition coil connectors.
Engine: Cranking
Voltage between terminal No. 10 and earth, between terminal No. 25 and earth, between terminal No. 40 and earth also between terminal No. 55 and earth.

OK: 0.5 - 4.0 V

Q. Is the check result normal?

Go to Step 8 .

Go to Step 9 .

STEP 8. Connector check: A-08 engine-ECU connector or engine-A-M/T-ECU connector

Q. Is the check result normal?

Check and repair harness between A-103 (terminal No. 3) No. 1 ignition coil connector and A-08 (terminal No. 10) engine-ECU or engine-A-M/T-ECU connector.
Check and repair harness between A-104 (terminal No. 3) No. 2 ignition coil connector and A-08 (terminal No. 25) engine-ECU or engine-A-M/T-ECU connector.
Check and repair harness between A-105 (terminal No. 3) No. 3 ignition coil connector and A-08 (terminal No. 40) engine-ECU or engine-A-M/T-ECU connector.
Check and repair harness between A-106 (terminal No. 3) No. 4 ignition coil connector and A-08 (terminal No. 55) engine-ECU or engine-A-M/T-ECU connector.

Check output line for open circuit.

Repair or replace the connector.

STEP 9. Connector check: A-08 engine-ECU connector or engine-A-M/T-ECU connector

Q. Is the check result normal?

Go to Step 10 .

Repair or replace the connector.

STEP 10. Check harness between ignition coil connectors and engine-ECU connector or engine-A-M/T-ECU connector.

Check and repair harness between A-103 (terminal No. 3) No. 1 ignition coil connector and A-08 (terminal No. 10) engine-ECU or engine-A-M/T-ECU connector.
Check and repair harness between A-104 (terminal No. 3) No. 2 ignition coil connector and A-08 (terminal No. 25) engine-ECU or engine-A-M/T-ECU connector.
Check and repair harness between A-105 (terminal No. 3) No. 3 ignition coil connector and A-08 (terminal No. 40) engine-ECU or engine-A-M/T-ECU connector.
Check and repair harness between A-106 (terminal No. 3) No. 4 ignition coil connector and A-08 (terminal No. 55) engine-ECU or engine-A-M/T-ECU connector.

Check output line for short circuit.

Q. Is the check result normal?

Go to Step 11 .

Repair the damaged harness wire.

STEP 11. Check the trouble symptoms.

Q. Does trouble symptom persist?

	Replace the engine-ECU or engine-A-M/T-ECU then perform the variant coding (Refer to GROUP 00 - Precautions Before Service - How to Perform Variant Coding ).

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

STEP 12. Perform resistance measurement at A-103, A-104, A-105 and A-106 ignition coil connectors.

Disconnect connector, and measure at harness side.
Resistance between terminal No. 2 and earth.

OK: Continuity (2 Ω or less)

Q. Is the check result normal?

Go to Step 13.

Check and repair harness between A-103 (terminal No. 2) No. 1 ignition coil connector and body earth
Check and repair harness between A-104 (terminal No. 2) No. 2 ignition coil connector and body earth
Check and repair harness between A-105 (terminal No. 2) No. 3 ignition coil connector and body earth
Check and repair harness between A-106 (terminal No. 2) No. 4 ignition coil connector and body earth

Check earthing line for open circuit and damage.

STEP 13. Check harness between ignition switch connector and ignition coil connectors.

Check and repair harness between B-240 (terminal No. 2) ignition switch connector and A-103 (terminal No. 1) No. 1 ignition coil connector
Check and repair harness between B-240 (terminal No. 2) ignition switch connector and A-104 (terminal No. 1) No. 2 ignition coil connector
Check and repair harness between B-240 (terminal No. 2) ignition switch connector and A-105 (terminal No. 1) No. 3 ignition coil connector
Check and repair harness between B-240 (terminal No. 2) ignition switch connector and A-106 (terminal No. 1) No. 4 ignition coil connector

note

Before checking harness, check intermediate connectors A-13, B-212 and B-229, and repair if necessary.

Check power supply line for damage.

Q. Is the check result normal?

Go to Step 14 .

Repair the damaged harness wire.

STEP 14. Check harness between ignition coil connectors and engine-ECU connector or engine-A-M/T-ECU connector.

Check and repair harness between A-103 (terminal No. 3) No. 1 ignition coil connector and A-08 (terminal No. 10) engine-ECU or engine-A-M/T-ECU connector.
Check and repair harness between A-104 (terminal No. 3) No. 2 ignition coil connector and A-08 (terminal No. 25) engine-ECU or engine-A-M/T-ECU connector.
Check and repair harness between A-105 (terminal No. 3) No. 3 ignition coil connector and A-08 (terminal No. 40) engine-ECU or engine-A-M/T-ECU connector.
Check and repair harness between A-106 (terminal No. 3) No. 4 ignition coil connector and A-08 (terminal No. 55) engine-ECU or engine-A-M/T-ECU connector.

Check output line for damage.

Q. Is the check result normal?

Go to Step 11 .

Repair the damaged harness wire.