Questionmy question is 2 parts:
Scenerio: Check Engine light came on Hyundai Accent GS 2002 (59K miles). This is a 16V DOHC engine. At the same time the light came on, my exhaust started to cause a racket. I took car to dealership to run diagnostic. I received from them a summary, not the actual codes. They returned to me to tell me my Flex Pipe was broken and I had a bad Upper O2 Sensor. I asked if they could be related, they said no, it was just coincidence.
My questions:
1) Can a leaking broken flex pipe be the cause of the 02 sensor reading bad? I've been told maybe, but I don't want to spend lots of money to fix a problem that isn't necessarily there and get taken advantage of.
2) If I get mechanic to fix flex pipe, and it does not help CEL or 02 sensor situation, can I replace the sensor myself with little mechanical knowledge?
3) If I replace the sensor myself, how hard is it to do, and where is the Upper 02 sensor located?
My goal is to be as cost efficient as possible, while solving my problem. I don't want to fork out the quoted $550 to fix the problem if I don't have to.
AnswerHi Jett,
Ok, first problem I see is that you returned your vehicle to the dealership. In my book that is a huge 'No-No'. The dealership is, uh, nice for buying cars but after the sale, all they want to do is reside in your pocket, right where your money is and they figure the longer they hang-out there, the more they'll get.
As far as your questions are concerned:
The crack in the flexible down-pipe most assuredly caused the O2 sensor to fail or read incorrectly. A crack or a break in the tubing between the manifold and the converter will not only allow hot exhaust gases out, but it also allows cool, engine compartment air into the pipe where the O2 sensor sits.
Ok, let me give you a quick background on O2 sensors. These devices don't detect Oxygen as their name implies. An O2 sensor determines the exact temperature of the gases in the exhaust. Cooler exhaust temps mean that the fuel mixture is RICH, getting TOO much fuel, so the computer reduces the injector pulse-width to lean the mixture creating higher exhaust temps. So an O2 sensor is really just a highly calibrated temperature sensor.
Now back to the theory. If cooler outside air is getting into the exhaust system near the O2 sensor, it will give false readings to the ECM, which will in turn alter fuel mixtures and ignition timing and possibly even transmission shift points based on the inaccurate readings causing the engine to operate erratically.
Since the other sensors would be disputing the O2 sensor readings with the ECM, the ECM would have final decision which sensor(s) to believe. Typically, the ECM will first acknowledge the MAP (Manifold Absolute Pressure - tests vacuum) sensor and the CPS (Crank/Camshaft Position Sensor - determines where exactly the crankshaft is inside the engine) to determine if the engine is running. Once the coolant temperature sensor registers that the actual engine temp is above a pre-determined point (usually 155 degrees F) the ECM goes from closed-loop operation (only reading particular sensors) to Open-loop where it reads and adjusts settings based on what ALL of the sensors have to say.
The problem is, when your ECM engages Open-loop mode, it immediately determines that the O2 is inaccurate and it puts the engine in what is called 'limp-home-mode'. In LHM, fuel economy suffers and erratic operation could result.
OK, onto question number 2. You may not be able to find that piece of pipe anywhere else other than the dealership, unfortunately. However, you could probably purchase that piece from them and have someone else install it. I believe the piece you refer to is flanged on both ends meaning it should be a simple bolt-on application. I would definitely try and locate that piece elsewhere first though. Most aftermarket muffler (this would be the ONLY time I'd send someone to one of these shops) shops will have a replacement piece at a much lower cost than the dealer item. Ok, it may not be as good if it is not OEM, but the initial OEM part didn't make the 60K mark, so how much worst could an aftermarket item be.
Question 3. The upper sensor is located at the top of or on the exhaust manifold which is bolted to the cylinder head of the engine. If it is accessible, you could probably take it out and replace it using a wrench, but if it is buried, as they usually are, you'll need a special O2 sensor socket to R&R it.
Cost effective repairs START at the shop you take your car to. Find a local, reputable ASE certified technician/garage in your area and take your vehicle to them. You'll probably spend less and get more.
My advice on finding a new technician is: Steer clear of 'chain' stores like Firestone, Sears, Pep Boys, Monro Muffler/Brake, Midas, etc. as they usually only employ ONE ASE Certified Tech just so they can say they do and chances are, that guy is the asst. manager or manager and is not in the store to diagnose/repair vehicles anyway. Find a service location in the link below or get some names out of the yellow-pages and do a drive-by. Garages that employ ASE Certified Technicians will be marked with the 'Blue-Seal' insignia. If unsure about whether a place employs Certified Techs, just ask to see their credentials. ALL ASE Certified Technicians will be PROUD to show and display their certificate(s).
Thanks for the question, I hope this information was helpful to you.
Fred
www.knucklebusters.us
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