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Discussion Starter #1
Ok i had an o2 sensor code the other day for p2251 negative circuit ground something issue...has to do with the heater possibly, problem is I just replaced it, not with the 170 dollar motorcraft i did the 100 bosch, i thought bosch made the oem motorcraft or is it denso?
 

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Discussion Starter #2
The new one might have 1k on it, but it came on while idling in a parking lot so maybe the heater dropped below temp...i notice when i come to a stop now my afr doesnt settle to 14.7, itll sit around 15.3 or 15.7 and if i just blip the pedal it evens roght out at 14.7 or 14.4, right qhere it shpuld be.
 

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Discussion Starter #3
Ok some more symptoms....like i said its got a slightly lean afr and i noticed my boost-vac isnt settling at 10.00 like it literally just was. So im leaning towards maybe the o2 sensor backed out alil so its pullin air in there..but why would my vacuum be off....im wondering if its the o2 sensor again and its responding slow. Thats what it almost reminds me of. I did search my code on here before making a thread but it was mostly all old noob stuff from like 14 and 15...to much crap to wade through...lol....anyways, has there been alot of talk about people having similar issues with non motorcraft O2s?
 

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Did you use anti seize? Could you have possibly gotten any in the sensor sample holes?

P2251 means that the PCM has detected a negative current discrepancy in the wide band oxygen sensor for bank 1. Sensor 1 denotes the pre-cat sensor. The negative current control circuit is a ground circuit.

You really need to go over the physical wiring and inspect the connector.

J
 

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Discussion Starter #5
Nope didnt put any antiseize in the sensor holes, it came prelubed and i let it at that, didnt put anymore on it. Thats what i figured, the actual wiring, but i think its the actual heater in the o2 thats causing it to react slowly which is my afr is reacting real slow. And i was doing some reading and the bosch o2 sensors parameters and values are alil different then densos, which i believe is who makes the fomoco motorcraft part. But yes i agree i need to look at the wiring...i dunno why all the sudden this wiring back there would have an issue but hey Focus ST right?
 

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Discussion Starter #6
So i went out again, let it sit and idle was fine the whole time, pulled out drove a mile and threw code for 0053, which heater resistance. I pulled the intake pipe off pulled the plug off, there is no corrosion or anything anywhere whatsoever. The o2 sensor is tight, i dont fuqqen get this whatsoever. Im about to the point im gonna throw my hands up and sell it, this so fustrating, ive dealt with the lil misfires and dumbshit and taken anally good care of yhis thing, and im just dumbfounded, dunno where to turn. I can work on a car and even wire a stereo, and build a computer, but im not about to start cutting into a harness unless i know for sure thats what it is. And i still would rather have someone else do it cause i dunno what the hell im doing when it comes to a wiring schematic. Who owns a shop remotely even close to york county that is trust worthy
 

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Discussion Starter #7
@SSgtjrobertson ok ive been doing reading and reading and not so much from the forums but actual like tech documents, that you would read...to the best of my ability. Anyways, like i said i did check connectors and wiring, everything looks good, but i went online and continued to read about those codes and i found out these cars have an O2 sensor heater fuse, which i got a code for that negative circuit heater resistance and the other one also low ground circuit ...u know them better then me....but as i was reading im really starting to think its the actual sensor because i found somewhere that said if it was an issue in the wiring then the fusedlink should blow...its not blown or blowing, so that leads me to believe that maybe i just happened to get a bad sensor, or at least a bad heater in the sensor.
 

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383910


So if you look at the diagram above you will see the F32 supplies power to some Key items. This is why you must be absolutely sure that the wiring in good working order (which you have checked)

Yes sensors can be faulty and to @Duece McCracken point the wide band O2 sensor for a speed density system is crucial.

The sensor itself relays it's information to the PCM and the heating elements ground does as well. Impact, excessive vibration, or shock can impact the sensor's life span. Poor manufacturing standards or parts handling can also be a cause of failures. (Just because you were careful handling the sensor doesn't mean that everyone else was after it was manufactured)

Change the sensor out and double check all wiring.

Let me know if you need model specific diagrams as the one above may not match the PCM'S pin outs.

J
 
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Discussion Starter #9
What should the o2 sensor read on the terminal with a multimeter? Oh n youll love this...still workinh on this o2 sensor issue, but youll love this i was chrckin the fuse for the o2 heater and ive now had a complete warm up and drove 10 miles of varying speed and i have accumlated 1 misfire ans that wasnt for 20 mins aftwr drivinf....wtf is gkinf on
 

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Discussion Starter #10
Yea and it mustve changed coz in my supplement it says F35 is the o2 heater sensor in the 18s
 

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383912

That is what you were referring to correct? Funny do you see what else is on that fused link with the heater sensor....evap can purge valve....ummm....interesting.
 

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Discussion Starter #12
Which i also just replaved that purge valve line before the o2 cause i had got a p0456 code...that all seems very fishy. So just curious if i would have to run a new ground for the o2 for the harness couldnt i just tie into the existing ground at the plug and add another ground to it? Or nada dont work like that...sorry if thats a dumb question.
 

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Do NOT modify the O2 sensor circuit!

The ground is a PCM controlled circuit. Splicing is an absolute last resort. No need of adding additional resistance into the wire.

Give me a moment and I'll check the 2018 diagrams for you. I just stepped in the door.
 

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Discussion Starter #14
No thats fine i wasnt going to touch ground...dont worry im not one to cut wires first then ask questions...hahaha. no i was just kinda curious for knowledge purposes.
 

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****s and giggles @SSgtjrobertson, ok when your looking at the schematic maybe you can answer a question for me when looking at the main harness plug underneath the fuse box cap under thw hood, there is a larger blue wire, the farthest pin to the outside near the fender towards the front. That one thicker blue wire was kinda jiggly in there, i pushed down tight into it, and kinda gave a lil tug on the harness it self towards the plug because ford had it pulled so tight it looked like some of the wires were about to pull out of their corresponding pins, so i pushed that done tight to makw sure everything was seated properly in the plug. So im still dealing witb the o2 sensor issue although it hasnt thrown a plug my afrs are just kinda dlow to react and im pretty sure its a bad heater, ive got a motorxraft xoming on monday. But i bought an autozpne one this comes with a warranty so i figured tomorrow ill swap it out just becoz thw last time i did it ran good for at least 2 week so as long as it holds up for 2 days then itll have the ford one put in. But what i was gonna say is i jiggled that wire before closing the store and then ran to the dispensary to pick sone new carts. So i sat and let it have 5 mins to warm up and then proceeded with a good 1 hr drive in total with full wots and cruises and everything. Hasnt thrown a code again. AND GET THIS, this is FUQQIN WIERD, in that whole hour i got 2 misfires thats it, woth warm up and everything, then i even shut it down for 5 mins ran in a store left drove anpther 10 mins zero misfires....dude wtf is happening. This is so wierd.
 
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****s and giggles @SSgtjrobertson, ok when your looking at the schematic maybe you can answer a question for me when looking at the main harness plug underneath the fuse box cap under thw hood, there is a larger blue wire, the farthest pin to the outside near the fender towards the front. That one thicker blue wire was kinda jiggly in there, i pushed down tight into it, and kinda gave a lil tug on the harness it self towards the plug because ford had it pulled so tight it looked like some of the wires were about to pull out of their corresponding pins, so i pushed that done tight to makw sure everything was seated properly in the plug. So im still dealing witb the o2 sensor issue although it hasnt thrown a plug my afrs are just kinda dlow to react and im pretty sure its a bad heater, ive got a motorxraft xoming on monday. But i bought an autozpne one this comes with a warranty so i figured tomorrow ill swap it out just becoz thw last time i did it ran good for at least 2 week so as long as it holds up for 2 days then itll have the ford one put in. But what i was gonna say is i jiggled that wire before closing the store and then ran to the dispensary to pick sone new carts. So i sat and let it have 5 mins to warm up and then proceeded with a good 1 hr drive in total with full wots and cruises and everything. Hasnt thrown a code again. AND GET THIS, this is FUQQIN WIERD, in that whole hour i got 2 misfires thats it, woth warm up and everything, then i even shut it down for 5 mins ran in a store left drove anpther 10 mins zero misfires....dude wtf is happening. This is so wierd.
1. Are you using speech to text? Because if not, good lord! I can't tell if you're in a hurry or if you're having a stroke.

2. Paragraphs, start using them or I will find you and beat you unconscious with your own shoes. (And don't pull what the last guy did either!, Switching to flip flops didn't save him. It added about an hour to the entire process.) LMAO!😂

We need to really make sure that all the grounds are good and the battery is in working order. I will do a write up about the O2 strategies a soon. I think that sensor may be damaged as well.

Let's make absolutely sure that it's good to do and move on from there.

J
 

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Discussion Starter #18
No dont tell anyone...but im usually driving....not saying anymore. Hahaha
 
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Give you give me ypur address ill let you beat me with my own shoes if you fix this issue for me.. deal? Shoe beatinf for wiring fix? Hahaha :LOL::ROFLMAO::giggle:
 

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Discussion Starter #20
Ok bear with me...cause this is about to get wierd... but the 2018 schematic your showing is that saying 32 as in F32 is the fuse that runs the oxygen sensor heater?

Because if that is so, then theres an issue with my manual, my fuse box and the wiring and fuses, cause something doesnt match.
 
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