P0171 code

Dilemma....can’t get my truck inspected because of the emissions. I’m trying to stay away from repair shops for $$$ reasons and I believe most are ripoffs.
I changed the bank 1 Catalytic Converter and o2 sensors because the codes read they were the problem. Now the p0171 code is registering. Inspection shop wants $120. for diagnostics. I’ve read it may very well be the MAF so I’m going to try cleaning it. No visible vacuum leaks. What’s the difference with the chemical make up of cleaners? I’ve read where isopropyl alcohol in a spray bottle will do the job as well as carb cleaner or MAF cleaner. Thoughts and experience anyone? Thank you.

 

I always just use CRC Mass Airflow sensor cleaner, just make sure you don't touch the wires.

 

Avoid the carb spray. MAF are delicate and expensive. Isopropyl probably fine but I'd stick with MAF cleaner. Besides that, it's probably not the issue. The MAF is common to both banks and the code is for bank 1 only. Can't hurt to try but use recommended cleaners. Might as well clean throttle bore and valve while you have it apart. Again, recommended cleaners. I don't know if these are coated but carb spray may damage coating. Do some homework first. If it's lean you may have o2 bad sensor, bad connection, bad ground, restricted injector. New sensors doesn't necessarily mean good sensors. Best test is put them on an oscilloscope and look at wave form, that test is clear cut but requires access to a scope, knowing which wires to back probe (or clamp depending on the scope), and what the waveform should look like. The code is telling you there's a problem upstream but it can also be a voltage to sensor problem or the sensor data to ecm is false due to wiring. That could be wiring anywhere in the circuit or at any of the connections related to the circuit.

Reading your description, you replaced sensors and converter but problem still exists. My thought is wiring or lean injector. Spark plug inspection might indicate lean cylinder(s) if that is the case. Try some fuel system cleaner after inspecting plugs. Sea Foam poured into the fuel tank.

Inspect power and ground connections, chassis grounds, battery connections, clean them. Inspect the o2 connections, look at the pins in terminals, try some contact cleaner (can't hurt). Inspect wiring as much as you can see.

Vacuum leaks can be detected with a light spray around intake and vacuum fittings with carb cleaner. A change in rpm indicate a potential leak but I've seen where a heavy spray can give a false positive. A leak is sometimes accompanied by fast idle but a small leak may not be noticed if the ecm can compensate by closing IAC a little.

These are simple low cost things you can try before paying the shop. Further diagnostics may require measuring voltage at sensors, cylinder balance tests, live data tests with a scanner, possibly measuring resistance on wiring from ecm to o2.

Sometimes is easier just to pay but you can eliminate a few possibilities pretty cheaply. Good luck.

 

On my 05 tundra i was getting the check engine light on and the dealer said it was bank 1 and bank 2 but they weren't sure. After 3 years of trying to get the light off to get it inspected i took it in and said fix it. Well they didn't change a thing. The mechanic decided to clean the throttle body and the light never came back on. I had the truck 13 years.

 

Thank you Phil, Rob, and Jeff for your input. I’ll pick up some of the prescribed MAF cleaner and try that along with cleaning the intake and checking the easy stuff first. I’ll be back for sure. Lol Thank you again and Happy New Year.

 

Hey Bill58,

Also check/change your air filter. Or if you have changed your filter recently. I fought the p0171 code for a while until i realized that it also ways seemed to pop after changing my air filter. Even though the filter was listed for my Truck it gave the code. I also have a 2002 Sequoia and swapping filter into that same engine was fine( no errors).

 

Sometimes aftermarket 02 sensors don't work. Try OEM if nothing else works

 

Thank you Bob & Gerald, I did replace the air filter because it was needed. The plugs were long overdue so I replaced them and while I was at it I replaced the PCV. Any vacuum line that looked shabby I replaced. No idea when the fuel filter was changed so I replaced it.
Question I have is do I need to reset the check engine light with a code reader or does removing the negative battery terminal suffice? From past experience I’ve noticed removing the battery terminal only relieves the problem temporarily, then bang, check engine light comes on again.

 

Disconnect the battery and pump the brake 5 times should draw all the volts from the system. That should reset the coad. If you have a Auto Zone close by they will reset it free

 

Thank you Gerald. I’ve never heard of that process before. I’ll try it. I just ordered a Foxwell nt301 code reader and it should be on Wednesday. Figured it would come in handy.

 

I am so perplexed. After replacing the four sensors and the bank 1 Catalytic Converter, the CEL still pops on after resetting so I changed the Plugs, PCV, Air Filter, Fuel Filter, replaced some of the vacuum lines after inspecting them, cleaned the MAF, added sea foam to gas tank. I put a code reader on it yesterday and codes P0171 and P0174 still showing. WTF, I’m getting no hesitation, truck has good power. Should I try a new or used MAF to see if that’s the problem or do you think one of the sensors are bad? Really not too familiar with what the live O2 sensors should read. Time is running out on the inspection extension they gave me. Will be suspended in a couple of weeks.

 

If there’s still a problem somewhere in the system how’s that going to solve it?
I reset it before and took it to the inspection station while the light was off and they said it still hadn’t cleared. I’ll try what you mention. Thank you.

 

O2 and MAF sensors can give incorrect readings if they're not the ones that the computer is programmed to read. When it comes to sensors, always make sure you replace them with OEM and/or genuine parts and not some other brand.

CRC Electronic Cleaner works just as well as MAF cleaner on the MAF sensor. It's pretty inexpensive too.

Make sure and check all of the intake components after the MAF to make sure there aren't any cracks. Even a little leak can cause 071/074 codes. They're a HUGE pain to track down. I've done it on other vehicles so I definitely know what you're going thru.

You can try the carb cleaner around intake parts trick, but the likelihood of finding a tiny leak that way is very slim. There are YouTube videos on how to make your own smoke machine. That is a pretty reliable way of finding them, but you have to generate enough smoke to be seen. Sometimes a leak is so small that the smoke is too thin to be seen. Also, sometimes a leak won't crop up after the vehicle is driven for a while, rendering any of these tests kind of useless.

Good luck, if putting in all OEM/genuine sensors didn't fix the issue then you're in for a slog. Here are a few things I've had to change to seal up a vehicle: intake manifold gasket, intake manifold plugs/caps, all vacuum lines (large and small), fuel injector o-rings, air distributor o-rings, dipstick o-rings, CCV system (this is a big culprit on some vehicles), intake boots, throttle body gasket, secondary air pump gasket, spark plugs, etc.

 

Jason, thank you for your input. I’m very discouraged. I could live with the CEL on if it wasn’t for the inspection aspect . I disconnected the battery and pumped the brakes 5 times to clear the codes let’s see if that works. Even if it does I’m not sure it will pass the emissions. Typically after shutting off the CEL it last a day or two. Time will tell.

 

In R.I. auto parts stores aren’t permitted to clear codes, they can only read them to tell you what “possibly” may be wrong.

 

Well the disconnecting the battery and pumping the brakes lasted about 14 miles. CEL is back on. Back to the drawing board. Errrrr
Codes now read P0172 too lean bank 1
and P0174 too lean bank 2
Thoughts anyone?

 

Hey Bill,

Just read through your forum and sympathize with your P0171... My 2000 has the same code for the last 6 months. Having had a 01 Taco before this, I'm really familiar with the MAF sensor codes. My Taco usually pulled a P0420 due to the fact I had an oiled K&N CAI installed that contaminated the sensor often, easy enough fix once I figured it out. Unfortunately for me, the 171 code I keep getting on the Tundra is not as easy. In my case, I am aware of an exhaust manifold leak which apparently is common on these trucks. My best guess is that this leak is actually inducing air somehow, and causing the 02 sensor to read lean... Just a theory, but it's an excuse for me to get some JBA headers on. FYI, I've already been through the MAF, PCV, Vacuum hose, plug, throttle body, etc conundrum to no avail.

Good Luck!

 

Hi Dan, thanks for the post. Talk about aggravating. I may finally have resolved it. I’m on mile 50 now after resetting the system with a code reader. I’m hoping to bring it to the inspection station by the end of the week as long as the CEL stays off. One thing I have learned is that disconnecting the negative battery terminal doesn’t really reset the system, it’s only a temporary CEL fix, at least from my experience. I hope to post positive results by the end of the week. Thank you everyone for sharing your CEL resolution experiences.

 

What did you end up doing to keep it off this long so far?

 

Phil, I don’t want to put the cart before the horse. I’m hoping this is the real deal this time. I previously posted a list of replacement parts that I installed, I’m now wondering if they were all necessary replacements. Some of course were regular maintenance like air filter, plugs, PCV, fuel filter. I could be wrong and will find out by the end of the week but I believe after replacing the o2 sensor/s I just needed to “properly” reset the system with the OBD code reader. I was told not to go the “disconnecting the negative battery terminal route” but didn’t listen. After several disconnecting attempts and constant CEL popping up again and again and again, I finally broke down and bought a $100. OBD and reset it. So far so good but I remain a skeptic until it passes emissions inspection.

 

Understandable haha I find your situation very interesting I got a check engine light for bank 1 stream 1 oxygen sensor heater circuit fault. Replaced the o2 sensor and pulled the negetive battery terminal and was good to go.

 

Phil, I was good to go as well, sometimes for 50 miles sometimes for 15 then bang, CEL appears. I wanted to shoot the light out. Lol

 

Time to celebrate! Lol
My truck passed inspection yesterday.
I can only speak from my own experience but I would recommend to all who’ve had an issue with p0171/p0174 codes to replace the less expensive parts first and then reset the CEL with a OBD CODE READER. I can’t emphasize that enough. I replaced part after part as small as some of them were and disconnected the negative battery terminal after doing so every time to reset the CEL and it would always come back on whether after 15 miles, 70 or miles driven. After resetting it with an OBD code reader and driving less than 50 miles it passed. I was thrilled to repay the $55 RI inspection fee. I’m not doubting other owners who’ve had success resetting the CEL the battery way it just didn’t work for me.

 

Congrats! Another opinion may be that all, or most of those parts needed replacing, and the engine/computer took some time to work out the mojo. Glad you got it worked out and thanks for following through with your problem/solution.

 

I recently had a code for catalitist system operating below threshold i don't remember the number but i would lose power. So i we to rock auto and ordered new cats and just installed them last weekend. Haven't seen the light come back on ( knock on wood) i ussuaus had to reset it twice a week.

 

Fred,
The plugs, air filter, and PCV valve were definitely in need of replacement. After my experience I just think it’s best to reset via OBD code reader. I bought a new AUTEL MaxiLink ml619 for $76. on eBay.

 

Matt, good luck with your new cats. What method did you use to reset your CEL?

 

I have an obd fusion code reader and it can do a performance test as well as show a dashboard. It Bluetooths to your phone.

 

Nice, makes diagnostics much easier that’s for sure.

 

That it does.