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Check Engine Light - It was my spark plug coil


I was on my way to work one morning and I dropped by a Royal Farms store to get coffee. I was all set to work and I started my car and pulled out of the parking space. I've noticed that the car is running rough and the Check Engine Light came on.

I remembered that there is an Advanced Auto Parts store nearby, probably about a mile and drove there slowly. I asked if they can check the code for my CEL and they did it for free. The code was P0305 and the associate said that it was a misfire on one of the cylinders. I called up my mechanic buddy and asked for an advice on what to do. My buddy said that it's either the spark plug or the coil. He told me to try replacing the spark plug first and if that doesn't work, try switching the coils and check if the code changes. I don't have any tools with me so I also asked if I can drive my car back to the house and he said yes as long as I don't drive fast.

I bought an NGK Iridium spark plug from Advanced before leaving. I just replaced the spark plugs less than a year ago so I still remember the brand. My home is about 10 miles away from Advanced Auto Parts and was able to get back safely.

I changed the spark plug on cylinder 5 and reinstalled the coil. I have an OBD-II reader so I was able to clear the code before starting the car. I then started the car but it was still running rough. A few minutes later, the CEL lit up again. I read the code and it's still P0305.

I then moved on to the next step of swapping the coils. I swapped the coil on the 5th cylinder with the one on the 2nd cylinder, cleared the code and restarted the car. The engine was still running rough and when I checked the code, I got a new one P0302. This indicates that the problem might be with the coil.

Looking to buy a replacement coil, I first went to NAPA Auto parts. They told me that they don't have anything in stock and said that they can have it by tomorrow. The price that they quoted me was $110 and I said that I'll think about it. In my mind, I knew that there was an AutoZone nearby and was planning to go there next.

At AutoZone, the associate was very helpful (his name is Jerry). He said that he doesn't have any in stock but he can also have it available by tomorrow. The price was also cheaper at AutoZone - $95. Jerry then said that he can check other AutoZone stores if they have it. He found one at a nearby store and he even called up the other store and told them that I will be picking it up. The store is about 15 miles away and Jerry told me to tell them that Jerry sent me there to pickup the part. I thanked Jerry for his help.

I got to the other AutoZone store and told them that I am picking up a spark plug coil and Jerry sent me. The manager got the part and showed it to me. I looked at it and it was the part I'm looking for and said that I'm taking it. At the cash register, the part came up as $95 and I already swiped my card. The manager said, wait a minute. Since Jerry sent me and Jerry is a nice guy, she will give me a discount. She took of 10% and the cost went down to $85.50. Whoa! I started from $110 at NAPA to $85.50... I'll take the $25 savings. Never had a day like this and I'm thankful for talking to Jerry at AutoZone.

I took some pictures of the spark plug coil replacement:

The faulty spark plug coil on the 2nd cylinder
Duralast coil from AutoZone
The new (shiny) spark plug coil
Removed the faulty one on the 2nd cylinder
Side by side (faulty and new)
New spark plug coil installed on the 2nd cylinder

I then cleared the code and restarted the car. The engine was running smoothly now. I drove the car around the block and the CEL didn't light up. I fixed the issue and it's good to have a mechanic friend who can always give you an advice on how to fix your car problems. Also, it's nice to meet people like Jerry who are always helpful to customers like me who are in need of help.

1 comment

automotive jack said...

There are a slew of other reasons why a check engine light may come on, too. Because it does not make sense for car manufacturers to have a dozen or so different warning lights, many times problems that do not have their own warning light get lumped under the check engine light category.

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