here's the saga. had a check engine light, went to auto parts store and had codes read. it was downstream o2 sensor fault..so I replaced them both. light did reset but it returned later. check codes again. this time upstream sensor fault and low volts. replaced upstream sensor again. reset ck eng light and it returned again with the same 2 faults as before. service manual says to check for 12v at the o2 sensor plug. only have 7 or so. this says that the ecm is shot. I find it hard to belive this could be true. anyone had the same problems??..if the ecm is bad where is the best/cheapest place to get one??

tip: check your exhaust system for leaks and/or cracks. I had my downstream O2 sensor act up on me. it was actually reading just fine. i had a small hole in my flex pipe (corrigated section directly after cat on exhuast manifold. it acts as a down-pipe off the manifold(p.s. I have a 2000 federal emissions... check to make sure if yours is federal or california emissions system... it'll cause you hours of frustration if you don't know.)). it turned into a complete break after a period of time. this caused my fuel economy to immediately decrease and my exhaust got MUCH MUCH louder. this is a good thing (the loud exhaust) if you ask me, but i was setting off car alams while i was parking my car at my apartment complex at night. kinda funny, but my neighbors and cops hated me. anyway... this is what your computer thinks as this series of events occur...

1.) downstream o2 sensor notices a small amount of excess oxygen in the exhuast system.

2.) this means that the engine is running lean and the computer needs to inject more fuel to cancel out this excess oxygen.

3.) the injectors put more fuel into the engine until the excess oxygen is cancelled out and everything looks normal.

4.) the computer now notices that the amount of fuel is greater than the recommened amount, given the amount of air being tracked by the Mass Airflow Sensor (MAF) [located right before the 45 degree bend before the throttle body{it looks like a black tube with wires comming off of it}] and the Intake Air Temperature Sensor (IAT) [located in the air filter housing].

5.) having said that, the optimum Air-to-Fuel ratio (A/F Ratio) is 14.7 parts air to 1 part fuel (14.7:1). when your injectors are spraying fuel to cancel out the previously mentioned excess oxygen, you are probably running a A/F Ration closer to 20:1 or possibly even 30:1, depending on the size of the hole(s). I was running at about 27:1-32:1 when i had my flex pipe break off.

if you have any questions on this, please do not hesitate to ask me... i understand that it can get confusing by just looking at text. In short, look at your flex pipe and your exhuast manifold. if either of these are cracked or broken, it's not too time consuming, but it can get pretty expensive. when i replaced my stuff, i used new, stock parts and it was about 500 bucks. the dealership will ask for about 300 for the manifold, and you can get the flex pipe online ("BOSAL" is the manufacturer) for about 100-120 bucks. don't worry about the gasket. if you get high-temp RTV and put a good coat on both mating surfaces, you'll be just fine. I acutally had my exhaust manifold gasket blow out before... i removed it, put some RTV on it instead, and i've NEVER had a problem with it... and that's the hottest part of the system. I actually use it for all my gaskets now... my girl's valve cover gasket, all my exhaust surfaces, even on a few other prats around my engine and car.. the stuff works wonders. anyway, let me knwo if there is anything that I can do to help... i'll do what i can or atleast let you knwo where you can go if i don't know the answer... good luck!

Andrew
aczeller@gmail.com

as far as I can tell, the exhaust system is ok. I replaced the ecm (ebay). still get the upstream sensor fault and low volts...this is really p me off. guess next step is to fork up for an oem sensor. currently running bosch, replaced it 2x. the downstream sensor is ok so far..how much is the oem sensor??

as to my knowledge, the bosch sensors are OEM, or at least very close. I used to work at a BMW dealership, so i learned a few of the shortcuts the dealerships go through to get parts and the actual parts they use... it woudln't surprise me at all if the dealership takes a bosch sensor and puts it into their box... i.e.: BMW takes castrol synthetic oil and labels it as "BMW High-Performance Synthetic Oil". last time i checked, the sensors are about 75-80 bucks or 90-100 bucks, depending on your supplier. also note... my flex pipe had it's hole on the TOP (facing the engine block), so i never noticed it. i know it was there because that was the portion with the most corrosion when i inspected the part after i took it off... one more thing. if you like LOUD exhaust, take off your exhaust pipes all toghter untill you can get the sensor(s). it doens't hurt your gas milage any and you can have a little fun with it until you decide to put it back on. if you like the sound of it after you get your new sensors, you only really need to leave on your flex pipe. the rest has nothing to do with anything except keeping the noise down. ;D

i'll get my inspection mirror and check the top of the pipe
thanks

check this out too... it's a Technical Service Bullitin from the factory concerning the Exhuast manifold. according to this, the dealership shoudl ahve started replacing these, free of charge, as soon as people started to bring their Elantras in for ANY kind of service. however, if the technician "forgot" to do this task and sent the customer on their way, he wouldn't be wasting his time, dealing with warranty pay, which is notoriously lower than customer pay... it's a flat-rate thing. anyway, look at this TSB and let me know if it helps.

later

Attached File(s)
 05_01_001.pdf ( 175.52k ) Number of downloads: 171

thanks. I suspect that if this is cracked it would cause my 02 sensor problem??!!

if this crack has occured, indeed, it woudl cause your UPSTREAM O2 sensor to act funny.this crack is VERY close to the O2 sensor and is very difficult to detect. about the only way to verify that it is actually cracked and the light isn't playing tricks with your eyes, woudl be to remove the manifold and check it out... according to the picture, it's on the back of the manifold, facing the block.

tip: pick yourself up some high-temp RTV from your local auto parts store before you do this. if it is cracked, you can apply a heavy coating to the crack, reset your computer, and it shoudl hold up for a while. make sure it dries before you start your engine up (so it sets right). it's kind of "ghetto engineering" or "farm fixing" if you knwo what i mean, but it'll work until you can get a hold of another manifold.

another tip: this thing will come out MUCH easier from the bottom... it did for me anyway. the studs that are on the bottom to meet with the flex pipe will cause clearance issues if you try to pull it from the top.

also, you may have to remove your power steering pump and bracket to get to the last bolt on the manifold.

and one last thing (i promise) there are studs comming out of the head. these studs are steel but the head is aluminum. the nuts are also steel. there is a good chance that the nuts have rusted themselves tot eh studs, creating a bolt of sorts. i woudl highly recommend you let your engine cool first, then spray a good amount of pentrating oil or liquid wrench. it may not completly seperate the nuts and studs, but it'll reduce your chances of having to re-set the studs to your block. i was working at a BMW dealership at the time i had to replace mine and i had to borrow some special tool (i don't remember the name) to put my stud back in to the proper torque, without damaging the threads.

if you want any more tips, just let me know. good luck

today I removed the heat shield and found a big fat crack!!..calling dealership today to schedule replacement

good luck... they'll be able to take care of it within a couple hours, pending the fact that they have it. no big deal. it'd be an easy fix, but can get a little messy with carbon deposits all over. it'll be about $300 for the manifold (it was for mine anyway), and as far as labor... figure 200 and you shoudl be safe.

got it fixed yesterday. when I scheduled it I also called the parts counter and had them pull one for me and hold it..runs fine so far. didn't cost anything either. however I had the timing belt replaced (60k). cost 295.00. not too bad

Well atleast my check engine light saga is similar, they originally told me mine was the evap. container, so I replaced it for the some of $125, installed it myself. Its very easy... They wanted to charge me $500, so ya. Anyways, 8months go buy, the light comes back on, go get it checked out. The mechanic says its my air intake, the kid who had this car before me put a cheap cold air intake, I mean cheap... It just looks like a cold air intake... Well my o2 sensor that is suppose to plug into the box, well its just hanging there nothing to go into. Which brings me to the other part of the check engine light, my car is crazy loud, and my gas mileage is sucking. I have a gigantic crack in my flex pipe, the mechanic says they can do it for $202, plus tax. I'm going to go ahead with them, because replacing it, would be to much effort myself... But my problem is, I need to get a decent priced Intake Air Filter Housing, or just a better intake.... Any Suggestions?

#1, your flex pipe... after it's replaced, the light should stay off. if it doesn't stay off and it throws the same code, you either have a faulty O2 sensor (highly unlikely), or you could have a crack in your exhaust manifold (covered under a TSB/recall). if it throws a different emissions code, it could be the UPSTREAM O2 sensor (the flex pipe is throwing a DOWNSTREAM O2 sensor code... let me know if you want more explanation). if it is the upstream O2, it could still be a crack in the manifold. it's on the back of the manifold, facing the block.

#2, your intake... there is no O2 sensor on your intake. it is either your MAF sensor (black cylinder with straightening vanes in it), or your IAT (intake air temp sensor). the IAT looks like a little plastic piece, about the size of your thumb, with 2 wires running out of it. the only way that i can see this being a problem is if:

A.) one or both wires has become broken within the insulation (like mine) and the sensor is no longer communicating with the ECU. this causes the ECU to run with the default IAT (-40 F) and the engine to run extremely rich (rich is better than lean). that could be the cause for your poor milage.

B.) your sensor is faulty. this causes irradic/faulty readings and creates the same issues as previously noted.

If your MAF sensor is bad, all you have to do is replace it with a new one and clear the code.

there is no problem with running a cold air intake if it is set up correctly. check your wires, connections and sensors per the specs on HMA Service.

Hope that Helps.

Later,
Andy

Andy,

I have having a similar problem with my 1997 Elantra. I had the Cat changed along with the O2 sensor after the cat, since it gave me low eff error on the cat and P0141 Oxygen Sensor Heater Circuit Malfunction (Bank 1 Sensor 2) code.

The mechanic asked me the change the O2 sensor. I think he has replaced it with a Bosch Sensor. but once i reset the code and drive it for about 10 miles, the check engine light come back on. I have tried resetting the check engine light several times and the same issue.

Please help

Ravin

the tech made you replace the sensor because that's just more money for him. the bosch sensor is the OEM replacement for most dealerships, and is the most readily available, so no worries about that.

the first thing that i would check is to make sure that it is the same code that is being thrown. is it still P0141? if so, then check all of the bolted connections, as well as the flex pipe. the cat shouldn't have done anything, unless it was clogged, so that may have been another mechanic scam.

if it is the same code, but all the connections are tight, and have gaskets or RTV in them, check to make sure that your header does not have a crack in it. i am not sure if 97's had the recall or not, but i know that 2000's did.

check the code to make sure that it is the same one. with a '97, there is a good chance that it may be a different problem all together... after all, it is an 11 year old car.

Later,
Andy

In any case, does this O2 sensor gives off any error codes such as P0335, P0563, and P1166? When my car airbag light and engine light illuminated and lowbeam out, I look under the hood and notice that the (02/2007) dealer installed upper radiator hose was leaking antifreeze into these sensor. I re-tightened the clamp (04/2008) and the leak stops. I don't know why the dealer did not detect this for there is a noticeable amount of hardened antifreeze under the hose and unto the engine block. Since 02/07 I have come 3 more times to the same dealership for scheduled maintenance and they failed to notice it. My last visit was this January 2008 and I am due for another one and I am thinking not to come back to that same dealership.

Andy,

Thanks for the response. The car still throws the same code P0141.

I was also referring to the Haynes Car book and in that it mentions that the downstream sensor only tracks the effeciency of the Cat. and since it comes after driving it for around 10 mins, I was suspecting the heater circuit within the O2 sensor.

In addition, the other culprits could also be the connection from the ECM to the Sensor, cause thats when the ECM actually startes communicating with the sensor. (i.e. after the sensor attains 600F).

Additionally, the mileage has increased quite a bit after all this change

Please advice if I am missing anything

Ravin