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A ghost living in my car!?

Hey guys, this is my first post and I am not that good with cars, so be easy on me.

Last year, I bought a 2003 Ford Focsu SVT with 120K miles on it. It is a very fun car to drive! but it had been giving me all sorts of trouble. Six months after I got it, the check engine light came on, and when I went to the mechanic, he told me that the front O2 sensor had gone bad. So, I replaced it, and it ran okay for a while. But then another code poped up, this time it was the intake manifold control module, and the rear O2 sensor. I didn’t have enough money at the time, so I didn’t do anything. After about a week, the car started leaking some sort of fluid from the clutch pedal inside the car! So I figured I have to take it to my mechanic, even if it meant squeezing myself into fixing it. He took a look at it and gave me an estimate of about 1300 to fix it. He explained that they had to replace the control module, the O2 sensor, the clutch master cylinder and the oil pan, as it was leaking some oil. Luckily, I had bought warranty on the motor, the tranny, and a bunch of other things, when I bought the car. I called them up, and they said that they will only cover the oil pan. So, I fixed that and asked my mechanic on the other things, on what can I not fix at that time!? and he told me that I have to fix the master cylinder, but the O2 sensor and the control module, they can wait a little bit. So, I fixed the important two, and went ahead and fixed the rear O2 sense it only cost about a 100 to fix. Unlike the module, which he wanted about 700 to fix! So the check engine light remained for the control module only.

Strangely, after about two weeks or so, the check engine light turned off by itself. I did not do anything, and I did not fix it! After that, the car ran great for a while, the check engine light stayed off, and it did not feel any different from the day I bought it. Then, suddenly the check engine light came back again, so I decided to put an end to this once and for all, and fix it. It got fixed and the car was as good as it could be!

Two months after that, about two and a half after I fixed the rear O2 sensor and the other things, the check engine light came back again! This time I took it straight to the dealership from where I bought it, and told him about everything. He promised me to fix it and I left the car with him for two days. After which, he called me and told me that they needed to replace the alternator, as it was getting bad very fast, and that the rear O2 sensor had gone bad again. But this time, he told me that he will get his mechanic to check it very thoroughly.

They replaced the alternator from the warranty that I had, no problems here. But his mechanic told me that he checked the O2 sensor and it is working perfectly! he checked all the wiring going from it to the PCM, and everything looks good! and he checked a whole bunch of things. His conclusion was that it has to be the PCM, so he ordered one for me, and they replaced it using my warranty. Then they took the car to ford and did the calibration and everything, and got me a set of extra keys. After all of this, the owner of the dealership wanted to make sure that he got it fixed, so he told me to let his mechanic take it for a while. He drove about 15 miles in it and told me that it is perfect! nothing seems to be wrong with it.

I was very excited and thought that this was all over! but surely enough, as soon as I turned the ignition after I got it, the check engine light came back on! This time it still reads faulty O2 sensor (heated or something) and now, an anti-theft code of some sort! I left it again with the dealership and his mechanic looked into it more and more, till the point that he told me, and I quote " man, there gotta be a ghost in your car!"

I am very sorry for this very long post! It is just very FRUSTRATING!! and I really don’t know what to do with it

Thank you very much!!

The anti-theft code might be related to the new key - did they program it properly before they gave it to you? The O2 sensor can be a lot of things, including a bad sensor, a bad wire, an ECU fault, or it could be that your fuel/air mix is bad, which is tripping the sensor. Or you might be burning oil, or not completely burning the gas, and that’s fouling the sensor. It’s really hard to tell from here, but I’m sure someone else will chime in with something more useful.

I concur w/@shadowfax, the anti-theft thing is probably related to the new keys. The dealer should be able to help you out on that one.

Yes, this seems very frustrating. I’d complain too. You don’t mention if the car has any symptoms other than the check engine light. Are there drivability problems, hesitation, exhaust smoke, rough idling? Or is it just the CEL coming on that is causing you all this grief?

O2 sensors usually don’t go bad time after time. That is probably the best clue you have. Either the ECU’s diagnostics are incorrectly reporting the O2 sensor is bad – when it is in fact good. Or something else is wrong. A bad PCV valve might cause this kind of problem. A stuck open EGR might also. A bad fuel pressure regulator is possible. A faulty fuel injector. And a bad head gasket could cause a fouled O2 sensor.

When the car says the O2 sensor is bad, ask your mechanic if they can veryify is in fact bad. If it is bad, ask your mechanic if it is worthwhile to check the PCV, the EGR, the fuel injectors, the pressure regulator, and the head gasket (usually they’d do something called a “leak-down” test).

They need to run a hot diagnostic on the o2 sensors. This means looking at the pre and post o2 sensors in real time when the engine is running and hot. The o2 curves will clarify whether you have a bad catalytic or a bad source of other contamination. Oil or excessive egr gas or excessive fuel will cause poor readings across the sensor pair. O2 sensors do not foul quickly unless there is a serious input of bad stuff like oil. Coolant does not effect them too much as the glycol burns off cleanly and the water is of no importance.

I have been through similar frustrations, first was a chrysler van that the pump that was used for emission testing was periodically failing, tg for warranty, Windstar read codes , but ended up being o rings in the plenum gasket, vs lean fuel mixture bank 1, the dealer was the fix as to superior code reading stuff I was told. Sometimes the dealer can do better than others IMHO

Thanks guys for all of your great inputs. For the anti-theft, I did it at the Ford dealership, so I would think that they knew what they were doing, being Ford certified mechanics and all. But it very much could be!! I have had troubles in the past with the dealership mechanics.

On the other hand, the other mechanic (who works at the dealership from where I bought the car, which is a privately owned small business dealership) he checked the O2 sensor by-itself and told me that there is nothing wrong with the sensor itself. Then, he followed the wiring of it to the PCM or the main computer or whatever it is, and he said that the wires look good and there is no short circuits or loose wires or un-insulated ones.

The car runs great, I haven’t seen any changes in drivability, or gas consumption, as it is still getting the same MPG. I don’t think that it is burning oil, as it doesn’t give a slightly blue whitish smoke when I suddenly accelerate. I don’t know if my mechanic checked the things that @GeorgeSanJose said, and I don’t know if he did the hot diagnostic test that @euryale1 talked about. But I don’t think that he did, even though he told me that he did everything he could think of , that is slightly related to a bad O2 sensor.

And also I changed the PCM, as he thought that it was causing the faulty code. The code went away when the mechanic tested it for a while and drove about 15 miles in it. But as soon as I got into the car, the code poped up again.

Thanks again for your input!