Checking / Testing
A direct measuring of the primary resistance is in many cases not possible.
This is caused by the integrated ignition module, which does not allow to directly access the primary coil.
The connector may look the same, but the signal on the "Signal" wires is different.
These pictures show the difference:
Separate ignition controller
The ignition signal can be measured on "Signal " connectors.
In this configuration, primary resistance can be measured in between each signal wire and battery voltage supply wire.
Integrated ignition controller
At the "Signal1" connectors only the "switch" signal (coming from ECM) can be measured. Resistance of primary coil cannot be checked.
The resistance of the secondary coil can be checked with an ohmmeter. The coil is tested with connectors removed.
Note: Some ignition coils contain diodes to suppress undesired sparks. If diodes are installed, resistance measuring is not possible.
Measurement of secondary resistance:
- Use the ohmmeter, check the secondary resistance in between cylinder 1 and 4, then in between cylinder 3 and 2.
- A resistance should be detected. If "open line" is detected it can be concluded that the coil is defective. (or diodes are installed!)
- If a resistance is measured, it does not clearly prove that the coil is OK. The coil might fail under vibration or when it heats up.