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Kenny Z.
Kenny Z., Ford Senior Master Tech
Category: Ford
Satisfied Customers: 5525
Experience:  Auto Trans, Drivability and Electrical Specialist
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mercury sable: o2 sensor codes that keep set check engine light

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Have a mecury Sable Wagon 97 with 3.0 OHV. I have had a problem with O2 sensor codes that keep set check engine light. The codes are PO135, PO141,PO155,PO161. Started off with one code PO161. Replace that sensor bank 2 sensor 2 then code set again PO161 so I figured I had wrong sensor and swaped both after converter sensors then code set PO141. Swapped back and then code set again PO161. Thinking again that I had wrong sensor I replaced with a new one on bank 2 sensor 1 again code was set. Did not have it coded this time so I replaced bank 1 sensor 2 with a new one. Again the code set again this time all four codes as stated above. I had replaced bank 1 sensor 1 about a year ago with no problem. I had the engine replaced about 4 weeks ago. Have checked the wiring on connectors and really don't see any thing. I now have software and hardware to scan my car with my laptop. I reset the check engine light and it came back on after a short drive. Set codes PO155, PO161 again. HELP!!!

HiCustomer Thank you for asking your question on JustAnswer.


You need to have the powertrain control module reprogrammed.There is a tsb out for this concern from Ford.No amount of replacing ego sensors will fix it.This is a dealer only procedure as they will be the only ones with the correct calibration files.Next time you get a code ask here first before replacing parts unnecessarily,might save you some $$$

Have a great weekend!



Customer: replied 8 years ago.
what is the tsb so I can look it up. I have alldata with all the latest tsb.
Just click on the link that says CLICK HERE in my first post.
Customer: replied 8 years ago.

Ok thanks for the information> I will take it to ford and get a reprogram if that fixes it then. I will click accept so you get credit for this information. Thank you.

Your welcome
Customer: replied 8 years ago.

Ok had a buddy of mine who works for ford come over yesterday and flash PCM. Looked like that took care of problem but this afternoon check engine light came back on with the same codes again P0135,P0145,P0155,P0161. I have a data view of all the PIDs for the o2 sensors, I have ElmScan on my laptop thats how I got these PID's. Would you like me to send them to you so you can look over?


Dean Kellam

Sure,if you can find away to post them here using the tree link for photos or the link for pdfs and url's.That is pretty surprising it did not fix it,it would be the first one I have seen.What kind of scanner did he use for the reflash? Did he verify it loaded?
Customer: replied 8 years ago.
I have to ask him. It was a same laptop that was silver in color. I know it had wireless because he used my wireless to download data from ford. I believe it was the tsb.Here is a picture of the PIDs----------------------------graphic
I can't open the picture,you cannot paste it into the text area.You have to use the tree icon and load it that way.
Customer: replied 8 years ago.
The current flow pids for the heaters should be closer to .7 - .9 amps.Looks like we have an issue either with the Vpower or ground side of the circuit.To have all 4 sensors coding together we know it is not a sensor and most likely not a ground as the pcm grounds the heater circuits individually to turn them on.The Vpower circuit is shared by all 4 sensors.This is circuit 361 (red wire).This circuit is also used to power the the fuel injectors as well as some other engine control components.I would start by checking voltage at the sensor connectors on the red wire with the key on.The circuit could have high resistance after the splice for the heaters so I would recommend testing the circuit loaded,with a test lamp if possible.Let me know what you find.We are also showing ground driver faults in the pcm on 2 of the heater circuits,but lets start with the power side of the circuit since we have low current flow on all 4 sensors.
Customer: replied 8 years ago.
I could only get to bank 2 sensor 1 and on the red wire had 0 volts with key in the on position, also got to bank 1 sensor 1 had 12.5 VDC on the red wire with key in the on position. My neighbor has a lift in his garage that normal I use to get under my car but he was not home tonight will check the other two hopefully tommorow.

Ok, let me know what you find. Remember,if you are checking voltage with a meter,it is possible to read battery voltage but that does not reflect the circuits ability to carry current under load.Also here is the wiring diagram,notice at splice 100 circuit 361 branches off to the 4 sensors,If you are missing voltage I would suspect the problem to be on the sensor side of the splice.That splice should be in the harness coming off sensor 11.





Customer: replied 8 years ago.
So you are saying use a test light instead of a meter?
Yes thats what I said in my post from this morning..."The circuit could have high resistance after the splice for the heaters so I would recommend testing the circuit loaded,with a test lamp if possible."Check the brightness of the test lamp at the battery then see if it is as bright while you are testing the circuits.
Customer: replied 8 years ago.
Sorry it has taken so long to get back my computer crashed and could not get back online. But here is what has been found I have no ground coming from the PCM module going to that circuit for the heaters on the o2 sensors. I guess the pcm is bad. I have a hot wire coming from the pcm to the heaters of the o2 sensors. I guess this is why I keep getting a fault on all 4 sensors.
Ok I thought that you said that you had zero volts at the heater hot wire.I would at least check the continuity of the ground from the sensors to the pcm before replacing it.
Customer: replied 8 years ago.
I have checked the continuiy of the ground to the sensors and its ok from the connector. Thats the reason I suspect the pcm. Now my question to you is I can not find a after martket one but I can get one from the dealer for 500.00. If I go to a salvage yard are the pcm for sables and taurus from 96 thur 99 the same and is it a difference between sedans and wagons? It a local yard here that charges a 1.00 do get in and pull your own part and I can get the pcm for 25.00. I just want to make sure I get one that matches the one in my car.
It has to be a 97 pcm and the engineering number has to match and it will need to be programmed at the dealer.Did you also verify the pcm grounds are all good also?
Customer: replied 8 years ago.

Ok the grounds to the pcm are good. Went today and pulled this pcm its the closest could find.( EEC-V ML2-30C 7F02 F7DF-12A650-EE 67MH30CB18-AC). The number on the original is (EEC-V ML2-30C F7DF-12A65-DF

67MH30CB17-AE 43223-658). The one I pulled is from a 97 I noticed when pulling different ones the the first four digits of the code changed with the year of the car. Like F7DF the 7 was always a 1997 car if it was F6DF it was a 1996 or a F8DF it was a 98 year. So I'm not sure if this one will work maybe you can give some info before I install it I had a couple of people who said they just pulled them and installed them and the car was fine. One guy said since this was a 97 it did not look for a VIN of the car and should work. What do you think?

The second digit of the prefix will indicate the year.I am not saying the car won't run but there are many factors in the calibration that will effect the way the pcm controls the powertrain,such as axle ratio,tire size,trans(ax4n or ax4s) maf calibration,injector flow,49 state or California emission package to name a few.If the vehicle has a pats key system then the pcm will need to be configured to the pats module (parameter reset) or the car won't start.You can try plugging it in but most likely the theft light is going to flash quickly and the vehicle is not going to start.This configuration will need to be done at the dealer even with the correct pcm.The vin does not have anything to do with it,it is the calibration data block that is in the pcm that is unique to the vehicle and there are many variations.The base programing of the pcm (rom) and hardware features are determined by pcm part #. The calibration data (ram) is what is programmed into the pcm depending on the calibration set up for that vehicle.That is why even with the correct pcm part# XXXXX calibration files need to be uploaded from the old pcm to the scanner and downloaded from the scanner to the replacement pcm as well as the pats configuration so the modules can talk to each other and allow the vehicle to start
Customer: replied 8 years ago.

What I ment to say earlier was not vin number but pats. Ok let me make sure that I understand what your saying. With this pcm as long as no pats system it should start and run? I need to upload the software from my old pcm to the one I just got? Just to make sure it has all tsb updates and the same software? If thats the case I can get my buddy to do that. The taurus I got this pcm from was just like my sable in that the engine type, tire size etc are the same. A least the tires looked like they may had maybe 1000 miles on them, I should have gotten them also but did not need the wheels. The wrecked car is from a local ford dealer so the emisions system should be the same . The only difference is it was a sedan and I own a wagon.

I can't guarantee it will start and run,I am not usually installing incorrect modules in vehicles,so to be honest I am not sure but I think it will if you get the pats figured out.If your buddy can do the software swap then he should be able to do the pats config also.The only scanner that I know of that can do that is the Ford IDS system.If he has that then you are good to go as far as programming goes.
Kenny Z. and other Ford Specialists are ready to help you
Customer: replied 8 years ago.
Ok thanks yea my buddy is a ford service tech, does a little side work. He came over before and flashed the orignal pcm with service update you recommended earlier in trying to figure out what was going on. So he should be able to hook me up again. Again thanks for you help and taliking me through these steps.
Your welcome and good luck