P0301 Error Code

Good point, my 50 year old truck has hydraulic lifters, no need to adjust valve clearance in all that time. I’m guessing that the switch from overhead valves to overhead cam configuration is what is causing the mechanical lifter method to remain common. And it’s not that big of a problem in my own experience. Both my VW Rabbit and Corolla have mechanical lifters, easy job to measure the clearances, admittedly a bit of a challenge to adjust them, esp locating the correct shim, but nothing that an adamant diy’er couldn’t do on a Saturday afternoon if they wanted.

For some reason Honda owners do that job more often than Toyota owners. Maybe it is just easier to do on Hondas. Ever wonder why Honda’s seem to be the preferred subject of cat theft? Wonder if the two are related somehow?

I will say it was easy to set the clearance. A set screw and lock nut rather than Toyota’s bucket tappet and shims.

There was NO way my S2000s cat would be stolen…car was too low. To low even for most jacks!

Honda SUVs and Prius get cat-nicked because they cats are so exposed and easy to chop off with a saws-all.

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My neighbor’s Honda SUV had its cat nicked. Started making loud noises on start-up, neighbor puzzled, I looked underneath, sure enough very easy access to missing cat. I wonder if Honda designed it that way as an aid to Honda owners, to make the cat easy to replace; i.e. fewer labor hours billed for the job? And the idea, while good for the owners in theory, later backfired. The cat on my Corolla more difficult to access.

A couple weeks ago here in San Jose somebody working along-side a small river found a cache of stolen stuff inside a hidden vault, dug into the bank. Many cats, along with lots of stolen construction tools found. Construction sites nearby. Tent-city, homeless area. $100 K stolen items.

George, based on what we see here, many folks can’t even be bothered to check their oil! With most automakers tripping over themselves trying to demonstrate that their brand is “cheaper to maintain”, forcing people to bring their cars in periodically for expensive valve adjustments is just silly.


Not suggesting Honda wants to make their cars easier to service b/c they think the customer is going to do that work. But easy to service means it makes the job take less time, therefore less expensive, which saves the Honda customer some $$$ over the years. “Total Cost to Own” is a parameter many car buyers use when deciding which car to buy.

Thank you for all the information. Very much appreciated.

so, I was able to take out all the newly inserted spark plugs and noticed the first one has a lot of black soot on the first cylinder plug (pardon my lingo as I have minimum knowledge of cars). I had replaced all the 4 spark plugs but looks like the first one is taking a beating compared to the others with just under 40 miles after replacing them.

Any ideas what would cause this ? The error code still is p0301 after swapping the ignition coils.



I’m still of the opinion a compression check should be run. You can throw parts at it for the next month but if the compression is down then it’s all pointless.
You refer to soot on the plug tip. Lowered compression can soot up a plug.

There is simply no way on God’s Green Earth to audibly check valve lash. The only thing that will let you know is if one is excessively loose due to excessive tapping. Valves that are tight (say .002 or whatever) are a heartbeat away or already there when it comes to valve/seat damage.

Shim and bucket is more reliable but what can happen there is that in the event of excessive looseness a shim can get tossed out and damage occur to the cylinder head, cam follower, and/or cam lobe. I’ve seen some cam saddle caps, cam followers, and even part of a cam lobe broken off due to a valve shim getting chunked out.

Even back in the days of the 280 Z cars those would toss the floating rocker arms out when the lash was excessive and the RPMs went up. Call the tow truck.

Honda even issued a TSB about tight valve lash but the bulletin is shy. It refers to seat recession but not stem stretch and it narrows the focus to a few years/models when it should apply to all of them.

It’s possible the soot on the no 1 spark plug is now causing the misfire after the coils were swapped, easily proved by swapping plugs, but my guess is there’s a problem with one of these

  • no. 1 fuel injector
  • pcm’s signal to no 1 fuel injector
  • pcm’s signal to no 1 coil
  • no. 1 cylinder has low compression

What order those are tested to determine the actual cause depends on how easy each is to do. I think if I had that problem on my Corolla I’d do the compression test first, testing compression on all four cylinders. (As OK suggests above). Not b/c I expect the problem is compression necessarily, but b/c that test is pretty easy to do, especially after the plugs have been removed already. Swapping injector 1 with another seems like a step in the right direction too. Take a careful look at the electrical connections to the fuel injector and coil as well, might spot a hidden problem.

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I took the car to the local car mechanic since I did not have the tools to do the compression test (in hindsight, I should have just bought the tools). I explained to them about changing all the spark plugs, replacing the coil and showing them the black soot around the spark plug 1.
They asked me if I reset the CEL after changing the spark plugs…I was like no, and shouldn’t you test for compression before resetting it.Although, I felt dumb for not knowing that we could reset the CEL light…all topics I read indicated the CEL light should not be reset and I could not even figure out a way to reset it on 2007 camry.
Anyways, short story they hooked it up to a computer and told me them did a reset and drove the car around for sometime but the CEL light did not come on. I drove may 30 miles since then and still no CEL light…shouldn’t it come back on if still an issue ? I am confused and worried now thinking maybe the problem is just masked by turning of the CEL but maybe need to go to a different mechanic to do a compression test or just but the tools and try it out.

The problem is being masked by the new spark plug, you need to find out why the plug got that way because until you do it will happen again.

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Just wait and see if it comes back on . As long as it is not flashing you can still drive for a short time . You may be OK and at least the shop did not get their next boat payment from you for no reason.

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You should erase the faults after repair, road test to see if they return. If you don’t erase the fault codes, it will take two drive cycles for the check engine light switch off, the faults will remain in the “stored” column for a period of time.

The spark plug may have become soiled while operating with the failing coil.

Good comments above. If problem remains the check engine light will eventually return.

Maybe some explanation would be helpful. When a cylinder “fires” properly, the fuel and air ( in the correct ratio of appx 14 parts air to 1 part fuel by mass) are introduced, then compressed by the proper ratio (around 10 to 1), the spark plug produces a spark, and finally the mixture ignites in a pretty severe explosion. Since all that action is mostly invisible to the computer, the way the computer determines whether the sequence is happening correctly or not, it measures the acceleration of the crankshaft immediately a spark plug fires. Using the crankshaft sensor. It’s looking for a significant increase in the speed of the crankshaft after the spark. If it fails to see that, it becomes suspicious there might be a problem, but to avoid annoying the driver about what might just be a glitch, it may not turn on the CEL right away. Instead it keeps checking to see if the problem continues. Every car’s computer algorithm is different, so it may take several weeks of daily driving for the CEL to turn on again.

Re: “could not even figure out a way to reset CEL on 2007 camry.”

There probably isn’t a way to do this on your car. It’s done w/a scan tool with that capability. DIY’ers who want to repair and maintain their own car usually purchase an aftermarket scan tool, $100 or so. Often disconnecting the battery will reset the CEL, but comes w/a big downside. Erases all the diagnostic codes. So when you take the car to a shop the techs there don’t have the benefit of the codes, more diagnosis time increases the fee. Battery disconnection can also cause other problems, like losing the idle parameters, or cause radio problems. So you were right not to do disconnect the battery to turn off the CEL light. If you want to do that, purchase a scan tool that has that function, or just let the shop do it for you.

I expect the reason your shop balked at doing the compression test, they think the problem is probably solved, and they want to save you some $$$. Shops deal with owners who have tried to do repairs themselves all the time, and know from experience often the owner doesn’t understand the diagnostic method well enough, and often misinterprets the results. Years ago I had a VW Rabbit w/fuel system problem, did what I believed to be the proper diagnosis & repair, but it simply wouldn’t start. Cranked fine, fuel ok, compression ok, spark ok, but wouldn’t catch and run. Had it towed to shop. The next day the shop called, said “why did you tow it here?, it started fine this morning, first crank attemp” … lol … turned out my fuel system diagnosis resulted in a lot of gasoline in the cylinders, and the engine was flooded. More time allowed the gasoline to dissipate.

Wrong George…

If the crankshaft sensor detects the crankshaft slowing down after the spark should have occurred, it indicates a misfire.


Tester above is of course technically correct. Reminds me of the time I did a presentation for a group of high tech executives. In explaining why one of their idea wouldn’t work, I made a minor arithmetic error. These folks jumped on this mistake like I had I had just claimed to see a dinosaur out the window! … lol. I pointed out the error was one part in 10,000, and this was ok when doing an approximate calculation.

Thank you everyone for your comments. This was very helpful…all good so far, I have >100 miles since the shop visit, nothing yet and will keep an eye out to see if the CEL comes back on.