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P0138 - O2 Sensor Bank 1 Sensor 2


bhmayor

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All,

I have a 2015 FPIU which is giving me a P0138 code and I was told it means that the O2 Sensor (Bank 1, Sensor 2) is bad on the utility.

I noticed that there is a huge range (from $45 to $340) of price for these sensors. Can any give me any insights as to what brands are worthy on the lower cost end of the scale?

Whence I ran into this issue on my 1999 Ford Explorer, I was told that replacing the gas cap might fix it (and so it did). Are there any other recommended things to check before replacing the O2 sensor on the 2015? Will replacing the air filter help me any?

If the sensor really does need to be replaced, where is the Bank 1 Sensor 2 located?

Thanks!
 

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imp

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All,

I have a 2015 FPIU which is giving me a P0138 code and I was told it means that the O2 Sensor (Bank 1, Sensor 2) is bad on the utility.

I noticed that there is a huge range (from $45 to $340) of price for these sensors. Can any give me any insights as to what brands are worthy on the lower cost end of the scale?

Whence I ran into this issue on my 1999 Ford Explorer, I was told that replacing the gas cap might fix it (and so it did). Are there any other recommended things to check before replacing the O2 sensor on the 2015? Will replacing the air filter help me any?

If the sensor really does need to be replaced, where is the Bank 1 Sensor 2 located?

Thanks!
@bhmayor

4 sensors are located 1 each at either end of the 2 Cat Converters, either side of the engine. Right Hand side is called "passenger" or "Bank 1"; LH is "Driver Side", or Bank 2. The sensors closest to the engine are numbered "1"; the ones beyond the Cats are "2".

Therefore, sensor 1-1 is right side close to engine, 1-2 is right side just past the Cat. 2-1 and 2-2 follow suit on the Driver's side.

Capice? imp
 


Turdle

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If it is possible, I would swap the 2 rear o2 sensors with each other, clear the code and go for a drive in hopes of resetting the code to the other side. This would show a bad o2 sensor. If the code stays, the cat converter is bad. You'll get to know your explorer a bit in the process.
 
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KayGee

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@bhmayor

4 sensors are located 1 each at either end of the 2 Cat Converters, either side of the engine. Right Hand side is called "passenger" or "Bank 1"; LH is "Driver Side", or Bank 2. The sensors closest to the engine are numbered "1"; the ones beyond the Cats are "2".

Therefore, sensor 1-1 is right side close to engine, 1-2 is right side just past the Cat. 2-1 and 2-2 follow suit on the Driver's side.

Capice? imp
Since the 5g explorer uses a transverse mounted engine, there isn't really a driver or passenger side to the engine. You may want to explain it in terms of engine orientation (from front or rear of engine) as I am sure someone is bound to get confused.

On explorer, bank 1 is near firewall and bank 2 is near radiator.

As for the op, you shouldn't be paying $300 for an O2 sensor. They are $35-70 from rockauto. Depending on your mileage, you may want to change all of them. You can swap them around, to see if you can isolate the problem, just be careful that you don't damage them when doing so. Once you factor in the time to do that and retest, you may find it easier to just replace them.
 
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bhmayor

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@bhmayor

4 sensors are located 1 each at either end of the 2 Cat Converters, either side of the engine. Right Hand side is called "passenger" or "Bank 1"; LH is "Driver Side", or Bank 2. The sensors closest to the engine are numbered "1"; the ones beyond the Cats are "2".

Therefore, sensor 1-1 is right side close to engine, 1-2 is right side just past the Cat. 2-1 and 2-2 follow suit on the Driver's side.

Capice? imp
Thank you for your posting it is both clear and entirely understandable to a Computer Scientist like myself. I was a bit surprised when I first got my truck to realize it did not use a gas cap when I first filled it up. I learned with my 1999 Explorer (some time back) that when the O2 light came on it was prudent to assure my gas cap was on tight and had no inner rotted rubber in it!

I try to understand and fix what I can on my FPIU, and your short treatise on the O2 sensors was wonderfully clear and useful. In short, Yes I do capice! :)

One other question I have is that I understand it is prudent to use some sort of special wrench thing (see below) and they all seem to be 7/8" and the specs for the O2 sensor say it is 22mm. I am more predisposed to get the exactly correct tool, but can anyone advise if it makes much of a difference? If anyone would strip something with wrong tool I am a prime candidate for that! :)

To quote someone from another forum (I lost their email or I'd give them full credit): 7/8" is 0.875" and 22mm is 0.866142" which means the 22mm would give a slightly tighter fit. What say you? I think I could go to a snap-on truck or that and get the exact 22mm tool, but is it worth the cost difference? Or is there a cheapy tool I can get (as I'll likely not use it again for a long time) that still is 22mm precisely and not 7/8" in size?

3/8 in. Offset Oxygen Sensor Wrench
 


bhmayor

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If it is possible, I would swap the 2 rear o2 sensors with each other, clear the code and go for a drive in hopes of resetting the code to the other side. This would show a bad o2 sensor. If the code stays, the cat converter is bad. You'll get to know your explorer a bit in the process.
This does sound like a good idea and once I identify the correct tool I will do this. No simpler manner by which to identify if the sensor is bad I think!
 


bhmayor

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Since the 5g explorer uses a transverse mounted engine, there isn't really a driver or passenger side to the engine. You may want to explain it in terms of engine orientation (from front or rear of engine) as I am sure someone is bound to get confused.

On explorer, bank 1 is near firewall and bank 2 is near radiator.

As for the op, you shouldn't be paying $300 for an O2 sensor. They are $35-50 from rockauto. Depending on your mileage, you may want to change all of them. You can swap them around, to see if you can isolate the problem, just be careful that you don't damage them when doing so. Once you factor in the time to do that and retest, you may find it easier to just replace them.
With all due respect (of which I am sure a lot is due to you for your knowledge), this confuses me a lot more than the other simple and clear explanation.

What is a 5G explorer? My explorer has no mobile phone equipment built into it except my phone which is on a cup holder stand and its LTE, not 5G. I have no idea what this means?

What does transverse mounted me? My engine is mounted normally not like an old VW or something, so I am not sure what to make of this. My car has a driver's side and passenger's side, and I can tell this when I get behind the wheel to drive it! And, for me, it is easy to understand where the driver's side and passenger's side is, but the firewall? Good lord, I had no idea my truck even had a router in it!

Yes, I am confused...but by your response not the original post. I am quite sure this is due to my ignorance, not the accuracy of your post so please do not be insulted, that is surely not my intention.

I am not a mechanic, I do not play one on TV, nor have I stayed at Holiday Inn lately. I am a simple Computer Scientist who could have a deep conversation about many deeply technical topics (Physics, Quantum Computing, Network Security, Cosmology, etc...), yet changing my battery or tail light bulb is about the tippy top of what I have learned about cars thus far generally. If I can learn to troubleshoot or fix something myself and I don't have to buy a 3 digit dollar amount tool that I'll use only once, I am open to doing so and learning more!

Thank you for responding and trying to be assured I was looking at things properly, I do surely appreciate it. Just its way over my head!

I also noticed that some other parts places have $35 - $50 O2 sensors upon further research. I also noticed I'd have to identify if they are male or female. Thank you for pointing this out to me.
 
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Turdle

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5G = 5th generation.
1991-1994 gen 1
1995-2001 gen 2
2002-2005 gen 3
2006-2010 gen 4
2011-2019 gen 5


tranverse mount means the engine is oriented sideways in the engine bay.
Due to this:


Bank 1 will be the bank of cylinders toward firewall ( wall between engine and internal cabin), the front 3 cylinders are bank 2.
 
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bhmayor

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5G = 5th generation.
1991-1994 gen 1
1995-2001 gen 2
2002-2005 gen 3
2006-2010 gen 4
2011-2019 gen 5


tranverse mount means the engine is oriented sideways in the engine bay.
Due to this:


Bank 1 will be the bank of cylinders toward firewall ( wall between engine and internal cabin), the front 3 cylinders are bank 2.
I will go and look at my engine later today, I never even noticed anything like that though I am quite sure you are right about a "transverse mount".
 


imp

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5G = 5th generation.
1991-1994 gen 1
1995-2001 gen 2
2002-2005 gen 3
2006-2010 gen 4
2011-2019 gen 5


tranverse mount means the engine is oriented sideways in the engine bay.
Due to this:


Bank 1 will be the bank of cylinders toward firewall ( wall between engine and internal cabin), the front 3 cylinders are bank 2.
@Turdle

Good that you mentioned this! I had completely forgotten Explorer had gone to FWD. Thanks! imp
 


bhmayor

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@Turdle

Good that you mentioned this! I had completely forgotten Explorer had gone to FWD. Thanks! imp
FWD - Four Wheel Drive? What does having Four Wheel Drive have to do with an O2 Sensor being bad?

Additionally, I was watching a video the other day on YouTube (see the link below) that was speaking about testing the heating portion of the O2 Sensor using a multimeter and checking resistance. Is anyone aware of what the pin out is for the O2 Sensor on a 2015 FPIU is and what the resistance ought to be for a functional unit?


I am also looking to getting a better code reader than I have so it can tell me things about faults with the sensors and the like when the vehicle is running. I am looking at an AUTEL AL539B and need to realize if it has most of the tests that this guy is reading with his high end Snap-On device.

https://www.autel.com/autelcms/u/cms/www/201904/11013731oydo.pdf
 
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Turdle

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Nowhere have I ever seen FWD used to refer to 4WD

until now.
 
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bhmayor

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peterk9

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What does FWD mean then?
Front Wheel Drive. The 5th generation Explorer is FWD biased with AWD capability when required.

Peter
 
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Justinwht

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What does FWD mean then?
Its contextual.
4WD lterally means the engine can connect to both the real wheel axel and front wheel axels (1). That would include the decades old manually twisting the handle on each front wheel; engaging a stick shift on hump; turning a dash knob (all above considered part-time 4WD where the handle and stick would be manual and dash knob would be automatic ); all four wheels connected all the time (AWD).

RWD is common for rear wheel drive passenger car and front wheels free to spin. FWD is power to front wheels and real wheels free to spin.

(1) (a) Power to rear wheels are distributed to via the differential that provides different rotating speeds (with a complex set of gears) when turning a corner (inside wheel rotates slower).
(b) front wheel 4WD had a simple gear that turns each tire gear - there is no differential distribution of power. This can be demonstrated by engaging 4WD on a hard surface and you can feel the front wheels jumping - for this reason it should only be used on soft or sliding surfaces like snow, sand, dirt, or ice.
 


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One other question I have is that I understand it is prudent to use some sort of special wrench thingI ... more predisposed to get the exactly correct tool ...i there a cheapy tool I can get
The "special tool" is a deep socket with slit on one side to place around the sensor cable. I couldn't get enough torque to break it free (PB Blaster penetrating oil overnight didn't help) so used an open end wrench and hammer. I forget if it is SAE or metric, I have both, find the one with least play.

The downsteam (between catalytic converter and muffler) sensors - Bank 1, Sensor 2 and Bank 2, Sensor 2 (if you have it) are easy to get to with jack stands; #1 sensors are a whole different problem.
 


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You don't have to buy the special tool. You can rent it for free at Autozone, O'Reilys, etc. I did that. Easy peasy. As to the O2 sensor it's a matter of preference on what brand you like. Just don't get a universal fit. I usually get OEM so I don't have any issues. Sometimes you have to other items (ie. fender liner) to reach the sensor easily.
 


bhmayor

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You don't have to buy the special tool. You can rent it for free at Autozone, O'Reilys, etc. I did that. Easy peasy. As to the O2 sensor it's a matter of preference on what brand you like. Just don't get a universal fit. I usually get OEM so I don't have any issues. Sometimes you have to other items (ie. fender liner) to reach the sensor easily.
When I wrote this post I was a little bit irritated, so I have re-written it. :)

I stopped at O'Reilly's and indeed they offered to "rent" me the tool (basically I buy it and they know it is getting returned for a full refund and its not a new tool they sell me). An odd form of renting (they call it that too), but, whatever, it works for me to use a tool for free. So thank you for the idea to do this. I do not mind buying tools I'll use a lot, but likely not this one as I don't make a habit of working on cars (unless its my own and an easy fix) and I've never had to replace an O2 sensor before.

Which O2 Sensor do I replace? - This has been a rather vexing question as I have two different opinions from this forum and a 3rd from Oreilly! Oy veysmear! Can someone tell me where the darn thing is? It is preventing me from even ordering the part!!!

The first thing I need to know (and the Oreilly folks didn't have specifics for a Ford Police Interceptor Explorer that had dual exhausts, so they were baffled) is the "Bank 1, Sensor 2" the upstream or downstream unit? Knowing this one term is critical in ordering the right part. Can someone clarify this for me? With all the chatter about tranverse engines and this, and Oreilly telling me Bank 1/Bank 2 really means passenger side vs drivers side (no one in this forum said that), I am fully confused and need some disambiguation here!

The next question is which O2 sensor is it, PLEASE, I have very low knowledge of cars, can we use terms like "driver's side" or "passenger's side" instead of firewall and whatever? I just have no clue and cannot imagine in my head what that means at all, especially with no diagram to look at.

Thank you very much to anyone that can give me a very simple, uncomplicated, easy answer that I can understand.

Thanks
 
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peterk9

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Just for future reference, the 'firewall' is that part of the vehicle's body that separates the engine compartment from the passenger compartment.:)

Peter
 
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bhmayor

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Just for future reference, the 'firewall' is that part of the vehicle's body that separates the engine compartment from the passenger compartment.:)

Peter
Peter,

I really do appreciate what you and others are trying to do and explain a lot of really deep knowledge to me. But I am just entirely confused, more than before I even started. At first yesterday I was ready to give up, but I have edited this message as I tried a new attack vector to figuring this out...I called the Ford Dealership near me.

The first Ford Dealership I called was completely clueless and could not figure out the part number I needed even with the P0138 Code, being told I needed an O2 Sensor and was given my full VIN #, so I hung up and called another one.

The second Ford Dealership I called was able to tell me authoritatively that Bank 1, Sensor 2 was downstream passenger side. Very easy to understand, all I wanted to know. Moreover, they gave me the Ford part number BE5Z-9G444B. The parts guy was then able to tell me it was the "Sensor 1" vs "Sensor 2" that determined if it was up stream or downstream, and the Bank 1/Bank 2 that determined if it was driver side or passenger side. The parts guy also said that it would be advisable to swap the sensors unless I had access to an advanced scanner. Swapping the sensors would authoratatively tell me if it was the sensor as the issue would move from Bank 1, Sensor 2 over to Bank 2, Sensor 2. If that happened he said, then your sensor is toast.

Bank 1 - Passenger side
Bank 2 - Driver's side
Sensor 1 - Upstream (before the catalytic converter)
Sensor 2 - Downstream (after the catalytic converter)

I am putting this information here so that perhaps one day it will serve some utilitarian purpose to someone reading this thread of postings.

Thanks again to everyone.
 
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