I’m so glad to find this website!… I own a 98 Ford Expedition XLT… 4.6L engine… It has 54K miles on it… Last week, while driving on the freeway, my “Check Engine” light came on… Vehicle seems to be running fine… I haven’t been able to feel any difference in performance… The vehicle starts up o.k… It accelerates o.k, as well… The Ford dealership wants me to bring the vehicle in to perform a diagnostic test… They’re charging $100 just for the diagnostic…

I was able to find a cheaper auto shop that hooked up a scanner and retrieved the engine fault code… The only code that showed up was “P0141, HO2S12 heater circuit fault”… According to the “Haynes Repair Manual”, there’s a downstream O2 sensor heater circuit fault (Bank 1)…

I assume I’ll need to replace the downstream O2 sensor… How many sensors does a 98 Epedition have?… I’m told there might be two upstream and two downstream sensors… Other’s tell me that there’s only one upstream and one downstream sensor… What does “Bank 1” mean?… Is there a way to check an O2 sensor with an ohmmeter?…


Hope you can help me with my dilemma…

 

Perhaps someone will come along that KNOWS for sure, but I'd be willing to bet money that "bank 1" is the "left" or "driver's side" of the engine.

There are 4 "O2" sensors on the truck... each side of the V8 has one before the catalytic {pre}converter and one after it. I'm not sure it's possible for an average person to test an O2 sensor since they require a high temperature to operate... basically a thermistor.

I recommend that you try disconnecting the battery overnight. Then, when you reconnect the power, drive around for a while and see if the MIL comes on again. Also, be sure to check your fuel cap and make sure it's on tight and is making a good seal to the filler neck. If, after this process, the light comes on again, you can buy a new O2 sensor at your local parts store and change it yourself relatively easily. Be sure to get some anti-sieze for the new sensor while you're at the store.

 

That was good advice NoMo, and you are correct to say that #1 is the left bank, so HO2s12 = heated oxygen sensor on the left side behind the catalytic converter, now I had to do alittle research to make sure that this was also not a catalyst problem code and it is not, this code is stating that the Oxygen sensor is open or shorted after one minute of run time, you can try the battery disconnect, but I would also look for some burned wiring or chard wiring or a oxygen sensor harness that got unplugged somehow, maybe it was never put together tight enough to begin with, I'm not sure on the location of the harness in comparision to the exhaust pipe, if all looks good and you checked NoMo's suggestions, get the new HO2 and install it.
Hope this help, Electric1

 

I have been lead to understand that bank 1 is always on the same side as no. 1 cylinder. Wouldn't that make bank 1 on the right or passenger side?

 

 

I honestly don't know.

 

I see we need to do alittle teaching, here we go,

HO2S11= Heated Oxygen Sensor Left Bank front sensor
HO2S12= Heated Oxygen Sensor Left Bank rear sensor or behind
Catalytic Converter
HO2S21= Heated Oxygen Sensor Right Bank front Sensor
HO2S22= Heated OXygen Sensor Right Bank rear sensor or behind
Catalytic Converter.

Ford only uses Heated Oxygen sensors in todays newer vehicle pcm's.

otherwise it would be 02s11 and O2s21, but it is not.

I don't know how to tell you any different than the manufacture has specified which one is where, you can call it anyway you want, but if you want to get it right when you are the one paying the repair bill because a Tech. installs a part on the wrong side and you pay for it, bring it back to find that the Tech, didn't know the difference between right and not right, how are you going to react. I bet real nice, right? then let's get it right. Information is worth alot of money, I am giving you this for free, because I want to and have been there trying to find out and did.

Left side is #1 Bank
Right side is #2 Bank

now since OBD2 has come to play, manufactures have had to go to one terminology of wording, so how can one manufacture like Ford make the right side just becausethe spark firing starts on that side #1 bank when Chevrolet calls #1 on the left side and still calls it Bank #1.I am telling from experience that the left side is #1 Bank and the right side is #2 Bank. Get out the code books and start studying, you will find left = #1. It is the same way with transverse (sideways) engines. Front of vehicle = #1 Bank, Rear of Vehicle = #2 bank. Now if you want to know what all this stuff does, let me know.
Have a Great new Year... Electric1

 

[updated:LAST EDITED ON 31-Dec-01 AT 10:11 PM (EST)]Thanks for clearing that up.

HAPPY New Year!

 

Electric1- Here is a quote from a training manual by Jendham inc. "Throughout the handbook, you will find references to HO2S1 and HO2S2. HO2S1 is used to identify the upstream oxygen sensor, while HO2S2 is used to identify the downstream oxygen sensor. Sensors are identified by either engine cylinder Bank 1 or Bank 2. Bank 1 always contains engine cllinder number 1 (Cyl 1)." I also verified this information by 2 other sources. One source was from a Mitchell manual component locater. A picture of the engine wiring harness and all of its various sensors shows the connector for HO2S11 (Bank 1 sensor 1) being on the right rear of the engine compartment (passenger side exaust manifold). It shows HO2S21 (Bank 2 sensor 1) as being on the left side (drivers side exaust manifold). I also own a complete set of factory manuals for my personal vehicle. In the factory wiring diagram component locater it verifies the information and picture locations stated in both Jendhams book and Mitchells picture with there own picture of the wiring harness and the locations of the sensors. So from this I get Bank 1 on most Fords is the right side and Bank 1 on most GM and CHRY products is on the left side. If all this information is wrong please advise me as to how I can get accurate information. Since I diagnose drivability problems for a living I need to know if the manuals I have are all wrong. I welcome any input into where Bank 1 is since our information appears to differ. I would also like to apologize to any one I might have led astray IF the information I am posting is in error. Thanks.

 

Nitro94, I investigated in the wiring charts and component location, and you are correct as to what the books are saying, thank you, I am going to investigate the Snap-On scanner tomorrow, I will be pulling my own Exp. in tomorrow and pulling oxygen sensor harnesses apart to double verify information on the scanner, I appologize for any miss information, I feel real bad about this. Electric1