Ignition Coil




Ignition coil provides high voltage for spark plug to generate spark to ignite the air-fuel mixture.

To achieve effective combustion in engine, consistent high ignition output and accurate ignition timing is required.

There are generally two main types of coil, "Stick Coil" and CRICs Coil a.k.a Coil On Plug (COP Coil). "CRICs Coils" are sometimes referred to as "rectangular coils" or "COP". The term "rectangular coil" or "COP" is commonly used in the market, it refers to all coils of similar construction. 

The characteristic of "CRICs Coils" is that the generated voltage is higher than stick coils. 

For cars sold between Years 2000 and 2010, stick coil is the mainstream as coil are require for replacement when used cars for 10-20 years. As of Year 2024, stick coil is still the mainstream.   

New cars sold around Year2015 are increasingly equipped with COP coil. Which estimate may take over and become the mainstream in Year 2025 onwards. 




Unique Selling Point

1. Highly Reliable

2. High Performance

3. Fuel Saving


DENSO Aftermarket Ignition Coil Types




Advantages of DENSO Ignition Coil

Comparison Against Competitors (Picture)

Let us take a look at the design and production advantage of DENSO Ignition Coil against competitors.





Failure Symptoms for Ignition Coil

1. Difficult Start Up

2. Acceleration Not Smooth

3. Unstable Idle

4. “Check Engine” Light is on


Failure Symptom for Ignition Coil

Investigation A (Behaviours of the vehicle)

When a monitor lamp turns on frequently, poor startability, rotational fluctuation of engine speed is big, poor acceleration, frequent knocking and so on, there is possibility of the ignition coil failure.

Investigation B (Measurement of the resistance and secondary output voltage)

STEP 1: Data accumulation of the new ignition coil
Measure the resistance and secondary output voltage of new ignition coils (more than n=5 are desirable) and calculate the mean as Rave (note 1), Vave (note 2).

STEP 2: Measure the data of the ignition coil that has a possibility of failure.
Measure the resistance(Rx)

Note 1 and secondary output voltage(Vx)

Note 2 of new ignition coil that has a possibility of failure.                                                                

STEP 3: Judgement
Calculate the data of Rx/Rave and Vx/Vave. When there is at least one data is in the range of 0.9-1.1, there is high possibility of the ignition coil failure.

Note 1
Measure the resistance between  IGt and GND.

Note 2 
There is no measurement condition specified, but it is necessary to measure STEP1, STEP2 on the equal condition.
Example: Room temperature, no load, power supply voltage 14V, frequency 10Hz and energization time 1.5ms


In event of coil failure, is it necessary to replace by set of Four?
If a failed coil is found in one cylinder, there may be other failed coils (including those that are about to fail).

Mixing a faulty coil with a newly replaced normal coil in a four-cylinder is not desirable because it increases the load on the normal coil and can cause premature failure. It also adversely affects other components (for example, plugs).

Therefore, DENSO would suggest to the car owner that if the product is used in such a condition, the repair cost will increase. As a result of the increase in the number of repair times or the type of parts that break down, the car owner will spend more, hence changing all 4 coils at the same time highly recommended. 




Risk of Imitation

Poor quality of materials in the imitation parts will make coil deteriorate faster than DENSO Ignition Coil. This might lead to crack in housing and the epoxy.

These two failure leads to low output of engine and also damage to the fuel delivery system.

By using DENSO Genuine Ignition Coil, you can be assured of best quality.