Automotive engines make use of a coil to produce a high voltage spike to fire a spark plug that fires up the air/fuel mix in the combustion chamber. If a fuel mix won’t spark in a cylinder, that triggers a misfire which will typically be seen by an engine’s PCM; setting off a fault code.
Moderate periodic misfires aren’t all that obvious, however, constant misfires will signal a rough running engine. In even worse cases, the PCM can shut down the ignition and fuel for a cylinder or a whole bank of cylinders which is typically called “limp mode” and will give off a flashing check engine light.
A failing coil is typically the main culprit as a reason for misfires, however, a number of things are also possible. Diagnosis will normally take about an hour or so at a shop.
The Cost of Ignition Coil Replacement
Here are some price quotes for the ignition coil replacement for some common cars utilizing a labor rate of $100 per hour:
For a 2008 Volkswagen Jetta with a 2.5-liter engine, the labor time for ignition coil replacement is half an hour. A factory replacement coil will cost around $4 and a Delphi part is $20. Overall project cost will be around $95 with OE parts and around $70 with aftermarket parts.
For a 2005 Kia Optima with a 2.4-liter engine, the labor time for ignition coil replacement is somewhere around half an hour. You should be ready to pay around $175 for a factory replacement coil and about $55 for an NGK part. Overall ignition coil price is $216 with OE parts and about $110 with aftermarket parts.
For a 2004 Honda CR-V with a 2.4-liter engine, the labor time for ignition coil replacement is also half an hour. A factory replacement coil will cost around $75 and a Denso part will be around $40. Pay a total of about $110 with OE parts and about $70 with aftermarket parts.
For a 2005 Saturn L with a 3.0-liter engine, the labor time for ignition coil (coil pack) replacement is closer to an hour for the front bank and 2 hours for the rear bank. A factory replacement coil pack will be around $130 and a standard part will be closer to $55. The total project cost with OE parts is around $220 for the front bank and about $315 for the rear bank. Utilizing aftermarket parts, the task would cost around $150 for the front bank and about $250 for the rear bank.
One question that shows up often when replacing a coil is whether it’s a good idea to change coils as a set or one by one. For the most part, there’s no reason to change a non-maintenance part before it has actually stopped working. Electrical parts tend to stop working unexpectedly, and not as a result of age and usage.
It’s also worth pointing out that there is a higher than normal failure rate on aftermarket coils; while the tech is relatively standard, making a coil that runs identically to an OE coil such that it can be driven perfectly by the PCM circuits is less simple. Whatever the reason, if parts are changed for the sake of upkeep or uniformity, in some cases keeping the old coils can offer an alternative in the not likely event of issues.
Different Types Of Ignition Coils
There are a bunch of different kinds of coil systems. The most common modern-day one utilizes an individual coil for each spark plug, that is fixed straight to the spark plug. This is called a “coil on plug” design.
Another design is pretty much similar because it has a coil for each spark plug. The difference is that instead of being replaceable separately, it is developed into a single system or a “coil pack”.
Some engines will utilize a coil for each set of spark plugs that are fixed to the coil by ignition wires. The oldest known design utilizes a single coil to fire many spark plugs; dispersing spark through a distributor and a handful of ignition wires.
What Else Is Suggested
Coils are typically changed when a misfire is discovered and the diagnosis shows that they aren’t producing sufficient spark to fire the air/fuel mix. This can result in a fouled spark plug.
Typically, spark plugs can be taken out and cleaned up which is a relatively easy process. However, spark plugs are also maintenance parts and reasonably affordable.
If they are close to their regular replacement time, changing them while servicing a coil is a reasonable and cost-effective thing to do, although it will mean an extra cost in parts and labor.
On a system that utilizes ignition wires to bring electrical current from coils to the spark plugs, it is pretty common to get rid of the wires either during the initial diagnosis or throughout the coil replacement process. Ignition wires can be pretty fragile, specifically if they are older and it is common and often, inevitable to damage them during the process.
Ignition wires are also part of the maintenance and fairly cost-effective. If they are in questionable shape and have to be changed, this is also a perfect time to change them.
In a worst-case scenario, you will have to quickly address a misfire and to be conservative and comprehensive with the repair work, a failing coil that results in a misfire can also damage the catalytic converter. A misfire sends out unburned fuel into the exhaust stream which is damaging to the coverings of the catalytic converter.
These typically cost more than $1,000 to have changed. The majority of the time, it takes a while for the damage to be visible. The engine constantly keeps track of the condition of the catalytic converter and will set a check engine light if it sees that the automobile emissions are not being properly handled.