Check Engine Light question...

[SG Wannabe]

I just got my oil changed on Tuesday, and the car is a 97 at around 84k miles...So I'm driving to college and all of a sudden I look down and the check engine light is lit. I pulled over, turned off the engine and started it up again, and it was still there. After I got to school I popped the hood and nothing seemed out of the ordinary. Any ideas what the problem may be?

[jaguax]

You NEEEED to use the search function.

But check engine light has to do with emissions. You need new oxygen sensors most likely. Autozone will do a free diagnostic in 5 minutes telling you exactly what the problem is, but I can almost guarantee that it's oxygen sensors. And please don't be pulling off of the road for a check engine light unless the engine is actually running abnormally. heh

[SG Wannabe]

Hahaha it wasn't on the HWY thankfully. I just pulled into a gas station :P

Any idea how much the sensor costs?

[e36bmdub]

bout 80$ a peice...you could go ahead and replace all of them however i'd try to find which one went bad

[1996Ken328IS]

Umm no. CEL is when the computer detects something abnormal in the operation of the engine. This does include emissions but also many of the components of the motor. You can buy a peke scan tool and get the codes yourself, or hit autozone up and they will read them for free. There is also a trick using the gas peadal that will get the CEL to flash the codes to you, but you will have to look that one up. This is likely unrelated to the oil change.

[SG Wannabe]

Alright...I'll take it in to Autozone on the way back from class. Thanks.

[jaguax]

Umm no. CEL is when the computer detects something abnormal in the operation of the engine. This does include emissions but also many of the components of the motor. You can buy a peke scan tool and get the codes yourself, or hit autozone up and they will read them for free. There is also a trick using the gas peadal that will get the CEL to flash the codes to you, but you will have to look that one up. This is likely unrelated to the oil change.

If his engine is not running abnormally, then it is pretty much guaranteed to be an O2 sensor. Sure the check engine light (at least in my Maxima) will signal if the engine is knocking bad or one piston or more is not firing, but you will definitely FEEL that because it would be running really rough. Other than that I believe the CEL is solely for emissions, vacuum leaks, MAF malfunction, little replaceable things like that. It's not something worth pulling over for unless you actually feel/smell something abnormal. If it's running no differently than before I would jump straight to O2 sensors, but like I said, Autozone will check that for you, free of charge. In your mileage range it is most definitely the sensors.

[OldCarGuy]

It could be many, many other things beside the Oxy sensor. Anything from a loose gas cap to air pumps or knock sensors, etc. Just pull the codes and see. The gas pedal trick only works on OBD-1 cars. Since yours is OBD-II and has 4 Oxy sensors, it can be pretty expensive to start throwing parts into it while guessing at the problem.

[BmotorMsportW]

If his engine is not running abnormally, then it is pretty much guaranteed to be an O2 sensor. Sure the check engine light (at least in my Maxima) will signal if the engine is knocking bad or one piston or more is not firing, but you will definitely FEEL that because it would be running really rough. Other than that I believe the CEL is solely for emissions, vacuum leaks, MAF malfunction, little replaceable things like that. It's not something worth pulling over for unless you actually feel/smell something abnormal. If it's running no differently than before I would jump straight to O2 sensors, but like I said, Autozone will check that for you, free of charge. In your mileage range it is most definitely the sensors.

Since when is a misfire not emissions related? dumping pure unburnt gas isnt bad? O2 sensor though possible is most likely not it. On the e36 a more common cause is the secondary air pump. the vacuum line which hooks to the valve will generally crack and begin to leak causing malfunction of the pump. just yelling out 02 sensor is such a bland diagnosis, there is an infinite amount of possibilties. Just because autozone can read the codes doesnt mean they can pin point the problem. An 02 sensor code does not always indicate a bad O2. Scan tools only lead the technician in the right direction to begin diagnosing

[1996Ken328IS]

Since when is a misfire not emissions related? dumping pure unburnt gas isnt bad? O2 sensor though possible is most likely not it. On the e36 a more common cause is the secondary air pump. the vacuum line which hooks to the valve will generally crack and begin to leak causing malfunction of the pump. just yelling out 02 sensor is such a bland diagnosis, there is an infinite amount of possibilties. Just because autozone can read the codes doesnt mean they can pin point the problem. An 02 sensor code does not always indicate a bad O2. Scan tools only lead the technician in the right direction to begin diagnosing

Let me get this crooked. When my cam shaft position sensor went out, that was emissions related? Are you suggesting that instead of haveing someone read the code and give you a place to start, it is better just to throw a bunch of parts at the car? Is the loose gas cap that causes a "mass fuel leak" error emissions related? I have a peke tool. It has a whole book of possible codes, are all of those just clever ways of saying "replace your o2 sensor". Please set me straight.:help

[BmotorMsportW]

I was trying to say reading codes is for a place to start. I am completely against throwing parts, it is a waste of money. cam shaft positioning sensor can cause emissions related problems. If DME loses cam signal it goes into limp home mode causing poor fuel efficiency and power loss, including increased hydrocarbon output. 02 sensors are just one of many many possibilities to the CEL problem

[1996Ken328IS]

Ahh. Looks like I was misunderstanding you. We are in agreement on the engine codes.

[SG Wannabe]

Just got back from Autozone...

"The PCM has determined that a large leak exists in the evaporative emmision control system."

Also, while pulling into my driveway, I noticed some small drip when I got out. Looked/smelled like fuel >_<

Also while at the shop the other day, they said my valve cover had a small leak, but nothing serious...it'd be $250 to get that fixed.

I called BMW and asked them about the check engine light and they said it'd be $110 to just look at the car. :(

[BmotorMsportW]

would you say the fuel leak is in the front, middle, or rear of the vehicle?

[SG Wannabe]

Not sure haven't gotten a chance to check. I just noticed it behind my car after I pulled into the garage.

[BmotorMsportW]

by the way, that fuel leak is your problem, evap system controls the fuel vapors in the fuel system and pressurizes itself as a self check to make sure the system stays sealed...good thing you didnt spend 400 dollars putting all new 02's in your car...

[SG Wannabe]

Do you know around how much that would set me back to fix? Any good places to fix besides stealership?

[BmotorMsportW]

any tech with a decent head on his shoulders should be able to find an evap leak if fuel is literally dripping as you said.

[SG Wannabe]

Alright I just checked, and it's leaking from the center of the car. The fluid is clear, very water like, it was a little bit dirty...odorless.

[M3ANMUG]

God damn I hate this...The dealership will charge me $300 to scan my CEL, and no place around has a special BMW scanner...and I can't get the damn gas pedal trick to work.

[Fadec40]

Alright I just checked, and it's leaking from the center of the car. The fluid is clear, very water like, it was a little bit dirty...odorless.

Center of the car is most likely the fuel filter area or a fuel line from the tank.

[SG Wannabe]

Any idea how much that repair bill will run me?

[OldCarGuy]

God damn I hate this...The dealership will charge me $300 to scan my CEL, and no place around has a special BMW scanner...and I can't get the damn gas pedal trick to work.

You can buy the scan tool new from Peake Research for $159, less for a used one on eBay