Causes of ignition coil failure
Although complete ignition coil failure will mean the system will not be able to generate the spark required to ignite the air/fuel mixture in the combustion chamber, there are often warning signs that become apparent that potential problems exist, which owners need a qualified professional to investigate, before they suffer a breakdown.
If an ignition coil is identified as defective, to avoid a replacement also failing, it’s worth exploring the reasons why it might fail, as this can help technicians, as they diagnose the system, to correctly identify where the fault arises. However, the vehicle manufacturer’s ignition system instructions should always be the first point of reference.
The reasons for ignition coil failure can be summarised under four main headings: internal short circuits, mechanical damage, contact failure and faults in the voltage supply. Internal short circuits can be caused by voltage overload due to a damaged or worn spark plug, an ECU control unit malfunction, general wear and tear resulting in a reduction of coil insulation, or excessive heat and abnormal engine vibration. When it comes to mechanical damage, this usually arises from an oil leakage from the valve cover gasket that degrades the insulation, but is sometimes from rodent bites from unwelcome residents! Contact failures are generally caused by water intrusion in spark plug recesses and voltage supply problems by a weak or failing battery, or faulty wiring.
The symptoms include no combustion, the engine warning indicator comes on, a persistently stalling engine, poor drivability, difficult starting in cold weather conditions and decreased fuel efficiency.
If the diagnostic trouble code (DTC) engine warning light is on, a visual check should be performed before a replacement is fitted. These checks should include mechanical damage, such as cracks and carbon tracks on the ignition coil body, corroded or worn plugs and cables in the wiring, a loss of battery power to the ignition system, and oil or water contamination anywhere in the ignition system.
The most common DTC fault code when using an OBD II car diagnostic tool is P0351 (Ignition Coil 1 Primary/Secondary Circuit Malfunction). The code P0351 is valid for the ignition coil in cylinder one, but if a similar problem occurs in cylinder two, for instance, the code will read P0352, or P0353 for similar problems in cylinder three and so on.
However, as well as a defective ignition coil, code P0351 could also have several other triggers, such as problems with the ignition circuit, spark plug or spark plug wire malfunction, an open or short in the ignition coil wiring harness, a defective wiring coil connector, a vacuum leak in the intake manifold or a build-up of carbon in the air passages of the throttle body. These factors further highlight the importance for technicians undertaking a repair to correctly identify the root cause of the issue, rather than simply replacing the first component in the process.
DENSO Aftermarket offers the independent service and repair sector a range of OE quality ignition coils, which encompasses block, distributor, stick and COP types and is therefore able to cater for the needs of many applications.
To quickly identify the correct replacement ignition coil, visit the DENSO website.
Further details of the DENSO ignition coil range are available at the Ignition product page.