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06 150k Lexus GS just popped up those two lights. A bit more rough idling on start up. Went to Autoparts to get an OBD scan and got a code P0302. They said to replace the spark plug.
My worry is that it might not fix the problem. If not, what could cause this light to come on?
The issue can be a faulty igniter (coil-on-plug), fuel injector, or spark plug. The first thing I would do is move the igniter on the identified cylinder and see if the code changes to that cylinder. If it does, then you know it is the igniter that has to be replaced. OBD readers are not expensive, you should buy one. Also fix this ASAP because a misfire can destroy your catalytic converter pretty quickly. The spark plug is the least likely cause.
I think Ill change the spark plug first and see if the code goes away because the ignition coil is pretty expensive($100).I had changed out the sparks on my other vehicle when it had the check engine light and it worked. But if it is the coil, is a used one safe to use?
Also the amount of inaccurate information on the internet is staggering. I googled if it is safe to drive with a vsc/check engine light and they said it was safe. Lol. I did drive from like 50 miles with the check engine light on. Hopefully nothing is destroyed.
Thanks Dave!
Hey Dave I think I’ll replace the OEM coil packs along with the spark plugs. Do you think I should replace the one bad one or replace them all? I used a multimeter to test it and it had a 32 Ohm reading.
I was reading about a post in MR2 forum and the guy said replacing all his coils made his car buttery smooth lol.
You should use the brand and part number spark plug that is listed in your owner’s or shop manual. It is always a bad idea to try a different type of spark plug than the car maker specifies. (don’t use a copper plug when a dual-fine-wire Iridium plug is called for)
You can also do well by going to the Denso or NGK website and lookin up the proper plug for you engine.
Regarding coils; I know too many folks who have had bad experience (short life) with aftermarket coils.
Wow, diagnosing the misfire and check engine light was a huge nightmare lol.
First I replaced the sparks with OEM parts because they looked really worn out. Didn’t fix. Then I replaced the coil which had the P0302 code. Didn’t fix. Then I kept moving the coils around. Didn’t fix. Cleaned the throttle body. Didn’t fix. This took alot of time and labor because I kept having to remove the parts and putting it back together.
But I think I found the issue. I think my valve cover gasket need to be replaced. Some of the old spark plugs had oil on them when I pulled it out and there was an oil leak on the front engine. The engine was also really low on oil. If this doesn’t turn the check engine light off, I’m definitely going to throw in the towels.
All in all, diagnosing is a huge pain! But the signs were all there from the beginning(oil leaks) but I over looked it. These challenges has really forced me to learn how the car works though. And I’ve gotten much better at finding a problem with the car.
If when you moved coils around, the misfire code doesn’t move from one cylinder to another (presumably with the weak coil), your problem is not coils. That is why you swap the coil pack before you buy anything.
I strongly doubt that the misfire has anything to do with the valve cover leak. Oil is non-conductive and is very unlikely to have any effect on the coils. Why throw in the towel? You have just begun the diagnosis process. You should get a copy of the factory shop manual and look up your fault codes. The manual will have a full diagnosis path to follow.
Likely causes are: bad O2 sensor, dirty MAF sensor, clogged fuel injectors.There is a definite leak on the valve cover gasket. At first I thought it was just oil from where you refill but it looks like its coming exactly from the gasket seal. Then there is oil on some of the spark plugs. There’s also alot of oil in the exhaust manifold.
If the new valve and spark gaskets doesn’t fix, Ill look into the your suggestions. Since the intake mani is off I’ll have a chance to check the injectors with a multimeter. Also I shouldve known that it wasn’t the spark coils because I tested them all with a multimeter and nothing out of the ordinary.
I think if one takes better care of their engine, diagnosing wouldve alot easier! This isn’t my car as its someone elses car. But the dirt and grime made me overlook the root causes. This has made me really stay on top of cleaning the engine because I’m someone who will wash their car every other day in the summer but totally ignore the engine bay lol
I assume you mean that there is a lot of oil on the exhaust manifold, not in. You certainly want to repair the leaks in the valve cover, but they will not fix you misfire issue. I strongly suggest looking in the factory shop manual before replacing the valve cover gaskets because the manual will tell you if and where you need to use sealant. It is common for corners to need sealant to supplement the gasket. Also, you really should follow the torque specs when you re-tighten the valve cover nuts or bolts. Unless you are an experienced mechanic, tightening by feel can lead to broken fasteners, stripped threads, or future leaks.
You can have weak coils even if they test fine with a multimeter.
This isn’t my car, Dave. The owners let me drive while they are on vacation. It’s a luxury car with alot of life left so I thought I’d be nice and detail the car for them and fix minor issues here and there. There was a large rear bumper dent that was there for over a year that I managed to remove with a heat gun. Looks 90% better lol. But while I was driving it, the oil was very low. So I changed it. The passenger headlight was also going out due to a bad ballast. I replaced that also. Then, a few days later I got the check engine light. Which scared the beejeebus out of me. But the owner said that it had came on before. But this time its not going off. So I had replaced the sparks, messed around with the coils, etc. I want to fix the check engine light for them before they get home in a couple of days. But it seems I just don’t have what it takes in the timeframe I have and the tools that I have.
I have learned one thing though from all of this – better to understand how things work because the upside is so much greater.
The CEL will not turn itself off even if you fix the problem, but you can do it with an inexpensive OBD reader.
Dave
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