Lean Codes Rarely Ever Occur From Faulty 02 Sensors!! P0171 P0174 

The general public believes: A trouble code IS A DIAGNOSIS. They believe a code tells you which part to replace. They also think a $40 code reader and a $13,000 shop scan tool are one in the same. They think "The mechanic hooks up his computer and this computer tells him which part to replace.

I work at a local auto parts store, people often come in and want their car scanned. After I scan a vehicle, I tell people that when a code appears, it is potentially A problem, but it may not be THE problem(s). It is just a place to start, and I recommend following up with a professional mechanic. Unfortunately, people like to load the parts cannon, and the auto parts stores know it. $$$$$$$$.

The last auto parts store I worked at, made it a point to express to customers that any specific part the code is naming, not to say in any way that it's the problem, we weren't allowed to advise the customer to purchase any part, all we could do is provide a print out of the code or codes from the vehicle and give it to them and tell them to take it to a mechanic and hope they know a reputable one that could do a proper diagnosis, and not throw parts at it, it felt like they had been sued for selling customers parts they ended not needing just based on what the code scanner said. They were very assertive about it, but I imagine other stores or individuals working in them, don't do that.

That's why it's important to pay a good mechanic that you want be a parts changer and end up spending more than the job is worth along with the aggravation that it will bring. Thanks Kenny for another great video.

Freeze Frame info can help determine when and under what conditions the fault occurred. I had a shop replace knock sensors on my truck. After that I got lean codes. I couldn't find a leak using the brake clean method until I repeated it the next morning when the engine was cold. When the engine warmed up, the intake expanded from the heat and sealed itself again. It wasn't tightened down properly. A freeze frame from scanner would have confirmed that the codes set when the engine was not up to temperature yet.

Please do not use chlorinated brake cleaner (I don't know which kind you had) for that leak test. If combusted, that can produce phosgene gas. Exposure to phosgene gas is a horrible way to die and usually fatal. I learned that rick with propane, but there are lots of flammable sprays that work. Water also works in the opposite way, by making it stumble.

On my old ranger those codes were from the IAC valve. Found it with a home made smoke machine. I fixed that about 10 years ago. Has not come back since and has always passed emmisions. Had to take a drive to complete the drive cycle and all monitors turned green. GREAT video.

Thanks Kenny. Great job, as usual! Keep up the great work you do.

I had a similar situation with my wife's 2012 Toyota RAV4. I checked the repair history and the Toyota dealer replaced the Downstream Oxygen Sensor because of the code P0138- Bank 1 sensor 2 high voltage (which means a lean condition). Same code by a independent mechanic shop which they also changed the Downstream Oxygen Sensor with a factory Toyota Oxygen Sensor. I looked up TSBs (Technical Service Bulletin) and found out that Toyota has a TSB for code P0138 only. They said to replace the Upstream Oxygen Sensor or Air Fuel Ratio Sensor because its stuck in the lean position. So I replaced the air fuel ratio sensor after doing a bunch of testing according to the TSB and the check engine light hadn't come back on since. Usually whenever you get a code for an oxygen sensor it means there is something wrong upstream of that oxygen sensor and not the sensor itself.

Good evening Mr Kenny, thanks for the video,oh and happy Monday, hope things went well. It's raining here in Tennessee as usual lol.

I use a small propane torch (unlit) to find vacuum leaks, it doesn't smell as bad and won't flash back like that stuff in the can if a ignition wire or coil is spark jumping

Good job...U did all u could do...Right on the mark Kenny

Man you are right about the spark plugs. I pulled one out after cleaning the TB and it was coal black from the dirt and grime. Like you said, it will burn off, but if you are changing plugs, clean your TB first, just a good practice, like part of the tune up, and your engine will run great.Good video, thanks

Good evening brother Kenny. Always enjoy watching my brother work because you are the man who 'keeps wrenching'. I have that same hose on my 2008 Ford Police Interceptor and I believe it runs from the "purge" valve to the intake manifold near the back of the 4.6 V8 in the CVPI. I'm just not sure what size fuel line I would need to make the repair like you did. I love the video.

Excellent video 👊🏻

Great insight thank you

those have a fuel filter in line on the left frame rail. they will run almost plugged but the first indication is lean codes on both banks. that hose is nla same one my truck needed. i used steel fuel line with a couple if short connector hoses for a nice clean look. yeah code readers ive learned to hate. better than nothing i guess

Hey, Kenny definitely learned something today. I have a car with a mass airflow malfunction, throwing a check engine light. I cleaned it with brake cleaner didn’t know you weren’t supposed to do that so I’ll give the electrical cleaner a try. Hopefully it works.

Great video.

Interesting way to test for a air leak Cheers mate.Also almost like Ivan at Pine Hollow Auto Diagnostics "no parts required".

I Comment as I watch. The proper time to test for a vacuum leak is on a stone-cold engine, an intake manifold can heat up and seal a leak in only a minute while SCAN PIDs are not yet working for FTs & O2s. Before I charge for a can of brake cleaner I am going to listen with my already paid-for mechanics stethoscope during the first-minute timeframe Once the engine has had a little time to heat up I will look at both LTFT & STFT to see if there is still a vacuum leak and perform the appropriate brake torque test. You have very good fuel control and -6 is not enough to throw a code based solely on the STFT. If you are not monitoring LTFT which is already richened up but bringing the overall FT into good control, does not actually mean the engine is in proper specs. I also do not believe in a shop bay test, I want a road test drive with the scanner monitoring appropriate FTs and O2s and MAF/MAP. If cleanable, get the reading before cleaning and again after cleaning somewhere down the road to see if I get a measurable difference on all my PIDs of value on the way back to the shop. In this case, I am going to stop twice to do two cleanings. What PIDs you have seen and what you show us should be the same, we have not seen the LTFTs or other important PIDs. Now you have found a hose problem and mentioned some cleaning, let's watch how YOU do your style..... FLATRATE style, do everything at the same time, and don't test after each repair/cleaning to see if the repair or each individual cleaning did anything to help measurements. RU-vidrs cannot claim FLATRATE, they spend far too much time BSing and not working FR speed. OK, now you admit to the LTFT bringing the vehicle into fuel control but not into spec or near zero. We can say that cleaning the MAF & TB is normal maintenance but when you do not document the corrections made by doing more than a single bit of maintenance, then it's hard to prove your point bit by bit and charge money for each bit and maybe in this case, the owner already cleaned the MAF??? A better visual inspection as taught by ASE training ought to have been done right away, you were already looking for a bad hose on the other side of the engine, ALL vacuum hoses ought to have been properly inspected and that one stuck out like a sore thumb, problem found, spray test did not work, replace visually old hose, PIDs checked and then standard cleaning of the TB & MAF and check PIDS for more improvement. When working on vehicles at a shop not owned by you, ALL work done needs to be annotated on the work order, and shop supplies appropriately charged for. In case the customer wants to complain about one little bit of work or comes back later to claim the usual, you touched it, you broke it. Thank you for all your videos that I am interested in based on the name of the title, which is to say, to some of your viewers or passerby folks, the name of the title is very important, in my case in 2023, for your channel, I watched 41% and annotated notes on all those videos that the title appeared to be a higher level of technician work. I do not do DIY or straight mechanical jobs, sorry but that is me, I am sure you have plenty of viewers for all your videos. I need to see more than one of the 4 S's, SCANNER, SCOPE, SERVICE INFO, SCHEMATICS to also give a higher rating and Subscribe to the Channel as well. I have seen some channels improve their output and say THANKS for this advice. Now I will see how the ratings go in 2024. My name for this video in my library: Ford F150 2002 5.4L TRITON SOHC P0171 P0174 Lean Codes Rarely Ever Occur From Faulty 02 Sensors I then put the repair here at the end of the title but you do not want to give that SPOILER as it might chase some viewers away. I then make a lot of notes with timestamps for future searchability with other pinpoint search keyword criteria to include some data of what is visible in a screenshot, maybe a scope waveform, location of a component, pic of the root cause of the malfunction, etc, such as your ROTTEN Purge Valve Vacuum Hose Location. In this shop, if you can answer, do you charge ONE HOUR for diagnosis and any remaining time within the first hour goes towards maintenance, or is the first hour only for DIAG and any work done, ALL extra time? Work on a component is not DIAG time?

Great info Kenny! I have a F150. The light periodically comes on. Parts store reader says exactly what you showed. They even suggested running cat-a-clean through a tank of gas. Said it could even be the sensors inside the catalytic converter. Worked for about 3 months. Engine light back on.

One of my cars was running Crappy in Closed Loop Mode, the Codes were saying Lean Condition on both Banks, yet it was producing more Black Smoke than a Diesel. It was being given as much Gas as the Injectors could provide. Two new O2 Sensors fixed the Problem

I use spray bottle of water. It will make it sputter and you can hear it. Less chance of a fire.

Too many parts replaced from plug in readers! Good self walked through video, hey ken your videos are great as I'm beside you ,show and tell ! Thank you! How's Mrs Wrenching doing?

A while back my daughter's car had check engine light. A scan indicated p0820, or Cat below theshold. The gasket between the cat and the pipe was leaking, and a scan of the oxygen sensor indicated a complete dropout at idle after being fully warmed up. A new exhaust gasket and a new oxygen sensor fixed the issue. The oxygen sensor had a broken wire on the plug which could not be seen in the car. The cat was fine.

Very nicely explained video. Have you thought about wearing a go pro so you can use both hands? Or getting a clamp for your phone. Appreciate the effort in your videos

My old truck had just a front oxygen sensor and one day the mileage dropped about 5 mpg. Nothing else changed, it ran exactly the same. After much searching I found the GROUND wire had broken off. I connected it to the engine real good and back came the mileage.

Yep, had this exact problem on my 2004 Mustang GT 4.6L it wouldn't run without holding the pedal to the floor. Found that same hose in the same condition, replaced it and cleaned the MAF sensor. Problem solved!

9:07 Is that regular fuel hose , which is about $3 per foot... Or fuel injection hose, which has more threads and built for higher pressures $10 per foot?

I like parts store mechanic.

Auto parts stores are for cash & carry sales only. AutoZone in New Jersey allowed themselves to become full fledged repair shops in front of stores using the no parking fire zone as their repair space. Way beyond batteries and wiper blades up to and including cv axcels. And not just a one time isolated incident.

👍👍

To its credit they said “check wiring” 0 parts

When you went to spray the MAF sensor you didn't notice how dirty the K & N air filter was. That wouldn't cause a lean code but should have been pointed out.

Kenny have you watched Speedkar99's videos, many of his videos are over 10 years old now, but I know he had a running gag with using his brother's toothbrush on his car repair videos!!😂

Has this F150 had any fix done for the recalled cruise control switch😬 If it hasn't the truck should be kept outside away from any garage or home, due to risk of fire. The fires from the faulty switch can happen even if the truck has been turned off multiple days. The F150 is one of many Ford, Mercury, Lincoln and Mazda vehicles that have been recalled for these faulty cruise control deactivation switches.

I always watch the o2 's switch from high to low . Then look at fuel trim. Then smoke it. I have seen intake manifolds leak on both sides from front to back on GM,s.

Did you consider just replacing hose, clear codes and run it a bit?

Had the same code on my Lincoln mk8 recurring. Was rear intake manifold leak not oxy sensor.

I have a better scanner now but before I did, I'd go to the parts store to read the codes if the light came on. Of course they'd ask if I wanted to buy the part right there and I never did. I always went home to check it because 1 I usually wasn't the first to have that issue and usually not rare but even if it wasn't a real known thing, it would steer me toward things I should check to make sure. Sometimes it was that simple, more often than not it was something related causing that code. And, I have never seen an o2 senser cause a lean code.

Fouling O2 sensors increasingly make your car run richer from what I've seen

Remember! Most throttle bodies are designed to flow air fully closed! The PCM is looking at the Mass Sensor reading, the MAP sensor reading and comparing that reading to calc the air/ fuel flow. However, the PCM assumes that the designed min air flow when the throttle body is closed is ALWAYS there! If the throttle body is dirty with soot build up, that min air flow is not there, so fuel trim is off. People and mechanics waste time installing MASS and MAP sensors that are perfectly good. The issue is usually a dirty throttle body! For example, a throttle body on a 2010 Mazda 5, there is 200cfm of air that the PCM expects to there at cold start up. That air is NOT there due to the dirty throttle body, but the PCM thinks it is! Car will have a rough idle, cold start will be balky. Mazda throttle bodies are dirty for that period as the crankcase ventilation is returned in front of the throttle body gumming up the works! On other vehicles the crankcase ventilation is put AFTER the throttle body so the TB hardly ever gets dirty as it’s mostly just clean air. Typical codes for a dirty throttle body can be “out of range” in description. But the parts store says it’s this part of that part and nope it’s just dirty TB. When it’s too lean or too rich, I usually check the TB first, and the air filter, clean if needed.

Pretty much a case of kill the messenger. E.G., the sensor says there is a problem with your engine, so you replace the sensor?

P219A 2013 Chevy Silverado 1500 P219A Chevy 5.3 Replaced injectors (Acdelco) Replaced upstream oxygen sensors (Denso) Replaced plugs and wires (Acdelco) Cleaned throttle body (Relearned Throttle body - scan tool) Replaced purge valve (Acdelco) Cleaned Mass air flow sensor Replaced air filter Running 5QT Full Synthetic 1QT Rislone Treatment Running range afm disabler obd2 Live data looks goods, MAF,MAP,No Misfires Fuel trims usually look good, oil pressure is good

Kenny why didn't you check to see if the purge was sticking open a bit

I have never seen a sensor read dead 0 on the downstream sensor. I haven't spent a majority of my years looking at sensor readings but 0...I have never seen. Most scanners I've used change values very fast but you snap-on doesn't. Is that 0 reading on the bank 2 sensor 2 normal? At 7:27 it starts to change but not much. But now at 7:35 the bank 1 sensor 2 goes from like 5 to 707 and yet that bank 2 sensor 2 stays at 0 ( millivolts). Now at 7:59 it starts to go up and at 8:36 it's at 618 after you sprayed that hose with brake clean.

I had a 2002 f150 with a lean code and it wasn’t a vacuum leak checked everything and it was a broken wire coming from the computer.

Name of the hose u replaced

Sad that people go to auto stores like this. Recently, I self diagnosed my truck, without taking the time to do it properly as I do know how to do. I ended up with a 1. New Battery 2. New rebuilt alternator 3. Belt & tensioner pulley 4. New starter. ALL FOR LESS THAN A REPLACEMENT STARTER WOULD COST AT A REPAIR SHOP.

Hey man off topic but I'm dying for some help...I need the best long reach ratchet that has the lowest amount of drag and swing....I need to tighten up an old egr tube flare nut and it is so tight I barely have any swing room...my cheap harbor freight ratchets just don't have the tight arc swing

Please get your glasses adjusted

What is a good scan tool for the home mechanic? I'm not a professional mechanic!

Use carb cleaner instead, it doesn't create gasses that are as nasty.

I’ve commented on this before parts store always says you got bad sensor never true the sensor is telling you something wrong that all it does is a monitor

The amount of people that condemn oxygen sensors for pretty much all driveability concerns is astounding. I think it is a holdover from the early days of single wire oxygen sensors on feedback carburetors where oxygen sensor fouling was a lot more common and the computers that monitored them really didn’t monitor them very well. Anymore, USUALLY, if there is an oxygen sensor malfunction it will set an oxygen sensor DTC. The other one that gets oxygen sensors incorrectly replaced is the P0420 and P0430 catalyst efficiency codes. In almost all cases those codes require new catalytic converters. In rarer cases there is a pinhole in the exhaust near the catalyst monitoring sensors. On a GM vehicle, the ECM won’t even run the diagnostic for a 420 or 430 if there are any oxygen sensor codes.

Enjoyed watching your video - thanks for sharing. You mention in your video about the 9:20 mark that rubber fuel line is ok to use for a vacuum application. Please be aware that while a rubber hose may be rated for a fuel line pressure application it may not necessarily be suitable for a vacuum application. Some rubber fuel line hose may work initially but may eventually be sucked closed internally under a high vacuum application if it is not designed to be used in a vacuum application.

I worked in parts supply for years and customers would want to know what the problem was and I always acted dumb even if I knew what the problem was as most of these customers would be fishing for free info then to go away and buy a cheap part somewhere else and mess the job up and then come back and blame you, The parts supply business was a lovely job until theses free loaders came out of the woodwork and spoiled it for everyone.

Kenny. Dont tell people to take their vehicles to the parts store period. Thats to the first mistake. Second mistake is the customer asking for a Diagnostic. 3rd...the customer believes the parts guy who is 20 yrs old. Reads the print out and tells the customer. This is the code. Sells customer the wrong parts. 4th. Customer returns again asking for a diagnostic test again. Same counter guy sells him a different part. The customer needs to ask. Are you a mechanic and how have you determined i need this part to fix my issue? The correct response is no. Im not a mechanic. These are the codes that are existing in your vehicle. Take it to a shop and have it diagnose properly.

Almost no one opts for DIAGNOSTICS until AFTER they spent MORE in parts cannon ammo.... They deserve it, for guessing. K&N filters can definitely cause this too....garbage.

I've been a Ford fan for years, but not a fan of the triton engines

why is there no need to properly clean a t-body i have others say the same thing i always remove and clean where it has proper air flow the build up in the t-body isn't good in my opinion

lol "grab your wife's tooth brush"

smoke machine money well spend two cents worth of advice

2.12.24. ⚠️Pay attention to what Kenney®️is speaking about, people❗️

No parts cannon needed, just plain old deduction and common sense...

You provide good information but don't give commentary over a running motor please?