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Inspection procedure 26: Ignition circuit system
 
 
 
 
CIRCUIT OPERATION
  • The battery positive voltage is applied from the ignition switch <vehicles without KOS> or the IG1 relay <vehicles with KOS> 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 connector terminals CIL1, CIL2 and CIL3.
 
 
COMMENT
  • When the ECM turn the power transistor in the unit to OFF, the 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 coil.
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 harness side connectors.
(1) Disconnect the ignition coil connectors and measure at the harness side.
(2) Turn the ignition switch to the "ON" position.
(3) Measure the voltage between terminal power supply line and ground.
  • Voltage should be battery positive voltage.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is battery positive voltage (approximately 12 volts) present?
Go to Step 3.
<Vehicles without KOS> : Repair or replace the connector(s), or check and repair the harness of open circuit, and short circuit in power supply line between ignition coil connector and ignition switch connector.
<Vehicles with KOS> : Repair or replace the connector(s), or check and repair the harness of open circuit, and short circuit in power supply line between ignition coil connector and IG1 relay connector.
 
STEP 3. Check the circuit at ignition coil harness side connector.
(1) Disconnect the ignition coil connectors and connect test harness special tool MB991658 between the separated connector (All terminals should be connected).
(2) Engine: 3,000 r/min
(3) Measure the voltage between terminal signal line (CIL1, CIL2 or CIL3) and ground.
  • Voltage should be between 0.3 and 3.0 volts.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the measured voltage between 0.3 and 3.0 volts?
Go to Step 5.
Go to Step 4.
 
STEP 4. Check of open circuit and short circuit to ground in signal line between ignition coil connector and ECM connector.
  1. Check the harness wire in CIL1 line between ignition coil connector and ECM connector at ignition coil 1.
  2. Check the harness wire in CIL2 line between ignition coil connector and ECM connector at ignition coil 2.
  3. Check the harness wire in CIL3 line between ignition coil connector and ECM connector at ignition coil 3.
Are the harness wires in good condition?
Replace the ECM (Refer to, Removal and Installation ). Then confirm that the malfunction symptom is eliminated.
Repair them. Then confirm that the malfunction symptom is eliminated.
 
STEP 5. Check the continuity at ignition coil harness side connector.
(1) Disconnect the 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?
<vehicles without KOS> : Go to Step 6.
<vehicles with KOS> : Go to Step 7.
Repair or replace the connector(s), or check and repair the harness of open circuit, and damage in ground line between ignition coil connectors and body ground.
 
STEP 6. Check of harness damage between ignition coil connector and ignition coil connector.
Is the harness wire in good condition?
Go to Step 8.
Repair the connector(s) or wiring harness. Then confirm that the malfunction symptom is eliminated.
 
STEP 7. Check of harness damage between IG1relay connector and ignition coil connector.
Is the harness wire in good condition?
Go to Step 8.
Repair the connector(s) or wiring harness. Then confirm that the malfunction symptom is eliminated.
 
STEP 8. Check for harness damage in signal line between ignition coil connector and ECM connector.
  1. Check the harness wire in CIL1 line between ignition coil connector and ECM connector at ignition coil 1.
  2. Check the harness wire in CIL2 line between ignition coil connector and ECM connector at ignition coil 2.
  3. Check the harness wire in CIL3 line between ignition coil connector and ECM connector at ignition coil 3.
Are the harness wires in good condition?
Replace the ECM (Refer to, Removal and Installation ). Then confirm that the malfunction symptom is eliminated.
Repair them. Then confirm that the malfunction symptom is eliminated.