****** engine light causes

[pickn4him]

Hello. I am once again seeking the knowledge stores of the forum. I have an '04 Legacy Outback sedan with 127K miles (EJ25 engine). I know this may be covered somewhere, but could a cheaper quality 87 octane gas cause a check engine light? Mine came on one day and hasn't appeared again in the last few days. I try to advise my wife to use name brand regular or midgrade but that don't always happen. I have never replaced the O2 sensors so without investing in a code scanner and pinning it down, I'm not 100% sure.

 

I also had to replace a passenger side rear tire last week after my wife found a big shard of metal that cut a 2 inch gash in the belting. I wondered if that would cause a wheel speed sensor on the ABS or AWD part of the computer to be "confused" since the tires were about 15K miles old and then adding a new tire that had no tread wear to the set.

 

Thanks in advance!

[GeneralDisorder]

Get a code scanner - it's less than $50. Check ebay.

 

87 Octane shouldn't cause a problem with a non-turbo. All EJ engines have knock sensors and should run just fine on 87. That in itself should not cause a CEL.

 

GD

[NoahDL88]

Non turbo Subaru's are designed to work with 87 octane, at least the 4 cylinders are. Running a higher octane fuel makes the ignition system work harder as octane is an anti ignition rating rather than a rating of the power the fuel can create.

 

The common misconception is that since powerful cars require premium an econobox will run better on premium.

 

While I avoid arco and the like, I don't put anything but 87 in any of my vehicles except the one that requires 91.

 

 

Anyway, cliff notes, higher octane could cause a check engine light, but its not likely, most likely you're looking at a cat-converter related issue, evap system or ignition problem.

[idosubaru]

best bet is to read the code. advanced auto parts, autozone, and other national chains read the codes for free.

 

be sure to post back here exactly what the codes are, not what they're interpretation of the problem is.

 

at that age and mileage there's any number of common check engine light codes and almost all of them are easy fixes.

[Fairtax4me]

Without the actual code we can't tell you anything about the cause.

However... often times if the CEL comes on immediately after filling up, it's because the gas cap is loose. So be sure to check that and make sure it is tight. Then go get that code scanned and post it here and we can help with further diagnosis.

[pickn4him]

Okay, here's an update.

 

The check engine light stayed off for a week or two and never came back until this past weekend and stayed on.

So, I had the wifey go by Advance Auto today and have the code read and it was something about fuel tank pressure (she said). Someone with greater knowledge of the codes might know more specifically. The guy cleared the code and stated that it may be because of the hot weather but I thought the gas cap should be vented enough to take care of that, shouldn't it? Could it be because of the mandated ethanol gas??? Would it be worth buying a new gas cap if the problem comes back, or could it be a gremlin in the EPA hose spaghetti gas vapor recovery emission control garbage? I've not touched any of that stuff and it is a sore spot as you can tell.

But anyways, any one else had that problem????

[davebugs]

Often it's an EVAP code and often caused by just not having the gas cap on correctly. Next time you get gas you get it on correctly. The CEL magically goes out shortly there after.

 

Leaving you to scratch your head trying to determine what "cured" the car.

 

For future reference the reader provided a P9999 #. Get that. Don't let them translate for you. Then you can search on that SPECIFIC code here.

 

Yes - gas caps do go bad.

[Qman]

Every so often the little line that holds the cap will get caught between the cap and fill tube. This will cause a code. If it pops up again, check that. Make sure you clear that line when you get fuel.

[porcupine73]

Also I notice you said you replaced one tire. Make sure you measure all the tires circumference to be sure they are within 1/4". (Not that it would cause the MIL to illuminate, but it could cause damage over the long term if the circumferences are too different).

[idosubaru]

like he said, write the code down and post here the actual code number.

[Fairtax4me]

I thought the gas cap should be vented enough to take care of that, shouldn't it?

Actually no. Filler caps are no longer vented due to federal emissions requirements. Hydrocarbon emissions in the form of fuel tank vapors have to be captured and stored by the vehicles evaporative emissions system, so they can be burned during operation of the engine. Part of the EPAs Clean Air Act. IIRC it was part of the CAAA of 1977 that made evap systems mandatory for somewhere around 1980-ish model year and later vehicles.

[johnceggleston]

depending on the code, which we do not exactly know, it might be the fuel filler neck. lots of cars in the salt belt that have to replace them due to rust.