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Discussion Starter #1
I recently took my car to an electrician because I was having problems with my car. It showed codes P0135 and P0141 so both O2 sensors were replaced. About a week later I took it to a shop and they hooked up the scanner and it showed two codes this time P0136 and P0141. So I took it back to the other guy so he would fix it.

Later he called me and told me that apparently some lines were not getting the correct voltage. The next day he called me and told me he didnt know why it was showing those two codes. He said all the lines were now OK, all were getting the correct voltage and judging by the smell of the exhaust, the mixture was good. Because apparently he got another code that said the mixture was rich.

I dont know much about car electronics, but this is what he told me could be causing it. he said he checked the computer and apparently it shows it's getting no reading from some O2 sensors. Apparently the computer should be getting readings from 4 sensors and the car only has 2. So he tells me that Sensor 2 in Bank 1 does not exist phisically on the car and that is why it shows the 2 codes.(it doesnt get a reading from that sensor because it is not in the car) He says only sensor 1 bank 1 and sensor 2 bank 2 exist, but no bank 1 sensor 2 or bank2 sensor 1. I dont know if this make sense.

My questions are, how many sensors do our cars have? Why would he say the computer registers 4 sensors when there are only 2 can it be that the computer was changed and one from a car with 4 sensors was put in my car by the previous owner? Is changing the computers that way even possible? What can I do to verify if my car has the correct computer?
I've seen other fellows who have gotten the P0141 code so I believe that sensor does exist in our cars. Cause this guy is telling me that sensor does not exist at least in my car. He says there is only one before the cat and one after it.

Any help would be greatly appreciated.
 

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My knowledge on OBD2 computers is not as good as OBD1, but I think I can still shed a little light.

Yes there are only 2 O2 sensors on Foci just like the mechanic said.

First off, the basic CPU is probably the same for all vehicles from X manufacturer. This means that on models with fewer devices monitoring the engine, there will be ports open. Yes it is possible to put a computer designed for more O2 sensors in a car with fewer sensors- however, I doubt it would even start since there are apt to be many other issues than just the different number of O2 sensors.

Voltage low, voltage gone then reappearing: sounds like a connection issue. I'd have him check the bulkhead connector inside the driver's fenderwell. Ford did not put any connection grease on the pins to protect the connection from corrosion, and the connector is not completely weather proof. As far as I know nobody has ever had a problem with the bulkhead connector, so it's not for sure, but it does fit part of your issues. I'm assuming, of course, that your mechanic physically checked the wiring from the O2 sensors to the bulkhead connector. An O2 sensor creates it's own voltage of less than or equal to 1v through a chemical reaction to oxygen in the exhaust, and it doesn't take much resistance, corrosion, or loose connection to stop less than 1v.

I hope that helps, and please keep us posted if he figures it out.
 

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^^ agreed... id start with the basics before you get too deep in the problem.. try the wring from the o2 sensors to the cpu first....
 

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Discussion Starter #4 (Edited)
I'll tell him and i'll keep you posted on what he finds. Thanks for replying.

So it could be that my car doesn't have its original computer? Is there any way to find out, any numbers on tags or things like that?
 

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Oh sorry... I forgot about that part.

Yes there is a numbered code on the computer you can follow. It is highly unlikely that a computer from another car was used in your car. First off, I don't know of any 4 cyl vehicle in the Ford line that has 4 O2 sensors. If the computer was from a 6 or 8 cyl, then other problems would arise immediately.

I have no idea where to locate the ECU in this car. I do think that the best idea to repair the car is to take it to a Ford dealer and bite the bullet. Ford mechanics may bave access to TSB's that could help them pinpoint the root of the problem, and also have the ability to reprogram your computer if there is some issue with programming.

Basically, check the other stuff first hombre. It is unlikely that the problem is in the computer, and even less unlikely that the computer was swapped.
 

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Discussion Starter #6
Is the numbered code you are talking about the three leters followed by a number??? The code mentioned in this how to article...

http://www.focushacks.com/index.php?modid=32

I'll tell him to start with the easy stuff before getting into something more complicated. Let me know if that is the code so I can look for it in the car and let you know what it is to see if it is the original computer. Or let me know which code you need and where to find it so I can let you know what it is to know if it is the original computer so I can rule out that possibility.
 

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Yes, the sticker inside the door jamb should match the numbers on the computer. I still have no idea where to tell you to locate the computer on this car. Mine is an 05 and I'm not sure if my computer is in the same place as yours. That guy could've been a little more descriptive about where it was located.

It is possible that you could have a different Focus computer than the one you're supposed to have, but I'd think it would be unlikely. PCM problems are very rare, but people who don't understand newer cars often blame issues on the PCM.

Your car is an SVT.. and it makes me wonder if there is only one computer used in an SVT or if the computers were merely re-programmed. You really should throw that question at the guys in the SVT forum. I'm sure one of them has the answer. That might save you some time.

Best of luck [thumb]
 
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