I changed my spark plugs today. Thirty minutes afterwards, I get a check engine light and TRAC OFF message. The codes that I read are P0174, P0171 and P1170. What are those codes, and are they related to my spark plug change? Also, I used the OEM Denso plugs. Are they pre-gapped to the recommended value?

 

Start by taking a deep breath and clear your mind. Go back and check all the connections visually and physically. Don’t skip something because your sure you did it right the first time. Maybe something just didn’t click in right. I’ve had to zip tie some together. Good luck

 

You probably need to either clean or replace the Mass Airflow Sensor (MAF).

you should disconnect the negative battery clamp before cleaning the MAF sensor. You would have to disconnect the battery after cleaning the MAF anyway to reset the ECU to adjust to the clean MAF sensor.

 

Also look for a vacuum line leaking

 

@lexo98 You were right. I forgot to put back in a tiny hose. Very embarrassed.

On a related note, one of my spark plugs looked like this:

Should I be worried about anything? The others didn't look so crusty.

 

I’m sure there are a whole lot of us that have made bigger mistakes than that. Glad you got it figured out.

 

Are you running 93octane or the highest you have available? Do you use any fuel additives?

 

You had something going on in that one cylinder that the other cylinders didn't have. That one spark plug looked the way it did because the cylinder had either too much air or not enough fuel. You had (maybe still have) an oxygen sensor, Air-Fuel Ratio (AFR) sensor or MAF sensor that needed (or needs) attention.

There is nothing wrong with your spark plugs and they didn't need replacing - they'll last 250k miles with no degradation in performance of fuel mileage. That spark plug can be easily cleaned up and it will be as good as new.

If you still have the same problem going on you'll have the same codes thrown again...and your brand new spark plug in that same cylinder will look the same as the one in your image. Your ECU was not happy with the inputs it was getting from one or more of those sensors.

 

After looking at the base of the plug where the threads are above your fingers, is that wetness? Did you spray WD-40 in the spark plug hole before trying to remove? Or by any chance was the plug very easy to remove? Have you ever replaced your PCV (Positive Crankcase Ventilation)? Do you ever notice sluggish acceleration? Lots of questions but you got me Wondering whats going on.. 😃

 

Standard question everyone never ask. What year and Mileage? Also..... what do the other plugs look like?

 

Only ~55k miles I believe. He said the other spark plugs don't look like the one he posted an image of. A bad fuel injector could be the culprit...

 

Clogged injector or wasnt tightened down all the way along with his PCV being old and clogged..but you would think they all would look similar. I say use some good fuel system cleaner (Lucas Fuel System Cleaner is what i use) along with some shell/chevron 93 or 91 octane and then give the ole girl an "Italian Tune Up!!!". The reason is; is that for most people (like myself) life gets mundane and repetitious to which the responsibility moves in and the excitment and thrill move out taking the fun and "**** it!!" Attitude with it. This in return makes us drive more responsibly by just giving the throttle enough gas to get up to speed and thats it. This causes carbon and combustion residual's to collect in places it shouldn't, one of these is the spark plug. So go drive your car like it was a rental and bang that redline through the gears....when doing this look in your rear view mirror and you will see black clouds that will make Ricky Bobby proud👍🏻. Alot of little random quirks or hiccups cars have can be solved with some full throttle punches.

 

Not if one fuel injector was the culprit. That engine, with only ~55k miles, is not going to have a clogged PCV. It's barely even broken-in. My guess is that someone had been messing around under the hood...

 

At least it's something problematic on that cylinder. Possible Coil acting up defective? But then I would think it would check engine code. That's a weird plug. Fouled and gummed. I definitely would check that cylinder again in 1k miles, and or mark and move that coil. Then look at both cylinders to compare to see what happens.

A bad injector could do that too. Something did it? I can't think of any reason someone prior would go in just 1 cylinder and muck up, and/or how they could produce that? I have seen something close to that on the Lincoln LS where water would get down in one plug cylinder due to the front window rain seal run down in just one cylinder, cause the rubber boot to mess up firing the coil then give a throttle body ecu code due to a short. Had that same pinkish color with black carbon just like that plug.

Also the PCV would not just effect just one cylinder only? Would it?

 

I would say the rear 2 cylinders or 2 rear cylinders on the driver's side get the most oil from the pcv system....