P0171 Solved, FINALLY!!

So I've been plagued with a P0171 code (lean bank 1).
Trying to be a mechanic, I read the code and started googling. Part after part, nothing.
O2 sensor
Plugs
2 Coils
MAF
Fuel injectors
Fuel Filter
Fuel pressure regulator

Finally took it to a shop and had them live data read it. Low fuel pressure. Bad fuel pump. $500 to swap out.

So I ordered a denso pump from rock auto. Took the bed off, and swapped them out. Truck is running good now. No code.

So glad that I figured out the code as I am going to be selling the tacoma, and didn't want to list it with a CEL. Just bummed that I threw away all that money when I could of just dropped it off for a $55 scan fee, $80 part, and an afternoon of wrenching.

Maybe someone will search P0171 and see this and not follow in my foot steps.

 

Good on you for adding to the collective knowledge. Often folks will fix their issue and forget to report back with the solution. If I ever see this code, I'll know what to check! Thanks!

 

Usually that is how things are when we try to trouble shoot...happy you were able to track down the worn out part.
So was the DENSO part number this.... 9500103?
That's the one with the strainer... I believe.

 

Thank you for the update/summary post with easy search keywords.

Too often the poster never checks back in and there ends up being a long thread where the last page of replies are, "was this figured out?" or any variation there of.

 

Yep, part number 9500103. Pump and strainer. I've never changed just the pump before, usually I get the whole assembly. They didn't have a Denso assembly though, so just swapped pump and strainer. Pretty easy, two hose clamps and you're done. Was a little worried when I opened the box though b/c there were about 15 little grommets, spacers, washers, etc... But those are for different applications.

I also usually drop the tank when I do a fuel pump, but figured I'd try taking the bed off since the tacoma bed is lighter then most. Worked out pretty well. Hardest part was getting the wiring free for the taillights since there are 15 snaps holding them to the bed.

 

Don't feel too bad as many shops would not have initially diagnosed it as low fuel pressure, either. Was the truck lacking for power? Misfiring? The coils and fuel injectors might have been a bit hasty without a misfire code.

My new buddy is the Launch CRecorder. $90. Led me to diagnose the cause of my P0171 as a bad air fuel ratio sensor (after the obligatory MAF, fuel filter, spark plugs didn't do the trick). The voltage on my AFS was stuck at .66v no matter what I did to introduce a lean or rich condition that should have had its voltage fluctuating to some degree. 100 mile test drive last night and no CEL! Yahoo. Especially since I need to smog it this month.

 

Awesome, you just saved me time/money and troubleshooting. I was just getting ready to start replacing a buncha parts. Cleaned my MAF and the light came on 4o miles later.. thanks for posting!

 

Good to know My truck is throwing PO171 too, cleaned the MAF and got a CEL 25 miles later.

 

Couldn't you have done a fuel pressure test to see if it was your fuel pump without having to replace all of that?

 

Coulda, woulda, shoulda I guess. At the time, the fuel pump didn't seem like the issue. Plus I've never had one just have low pressure for an extended period of time. From my experience it has either just stopped working immediately (no start), or lost pressure rapidly then quit. Truck ran fine with the code. 80mph on interstate just fine.

P0171 read out turned up lots of hits. Fuel pump rarely showed up. I googled my eyes out, trying everything in sequence of most common cause to least.
It was almost guaranteed that it was the O2 sensor. After that, I just followed the list. I should of took it in after the O2 sensor, instead of throwing money at parts. If I would of had the low fuel pressure knowledge off the bat, I would of done the pump first.

 

That's pretty much what I'm going through right now lol. I was getting the same code as well as p0174. I replaced my air filter housing (was cut up) and replaced the MAF sensor. Got rid of the CEL for maybe 2 minutes. Then it came back on and pulled a code for the o2 sensor. I'm saving to get it so I can finally have the CEL off. Had it on for a year (since I got the truck)

 

Which O2 sensor?

 

1st one

 

Thanks so much Josh for info. I bought a 2002 Tacoma a month ago and nothing but P0171 code, ugh.

Replaced,

Both O2 sensors
Plugs
MAF
Fuel Filter

and nothing. I'm taking to Toyota dealer today and for $70 they run a diagnostics check.

Could be the fuel pump? Hope so. lol...


I'm getting awful gas mileage right now.

Stan

 

You can read live data with this:

$22 Foseal Wifi OBD2 Scanner, Car Code Reader Check Engine Light Diagnostic Scan Tool for iOS and Android

https://www.amazon.com/Foseal-Scanner-Adapter-Diagnostic-Android/dp/B00W0SDLRY

It connects through its own wifi to your phone / tablet. Androids use the torque app and iOS uses the car doctor app. I've been messing around with mine for when I do have to diagnose a problem so it's already familiar to me.

 

i had this code on my tacoma . cleaned the MAF sensor and replaced the MAF sensor gasket, and its gone, check gasket mine was cracked and air must of been sucked through the cracks around i,t had to buy from dealer

 

So I am getting P0171, but only after driving on the highway for 20-30 miles, and then it'll turn off after a week or so.

Spark plugs new
MAF is new

Does the only highway driving trigger mean anything significant?

I haven't noticed any loss of power, poor fuel economy, or anything else really.

 

Great post OP (like others said, contribute to the knowledge) but wait... There is a PID for obdII logging that shows fuel pressure? Or was it figured out by seeing a really high fuel addition trim just to hold idle?

 

@SpeedoJosh thank you for creating this thread! You just helped me solve months of problems after I upgraded my fuel pump and installed a supercharger! I was getting this code (along with bank 2) and no one was able to figure it out until I suggested testing the fuel pump. Turns out the shop that installed my SC kinked the hoses coming from the tank causing fuel delivery problems. Thanks brother!

 

Those sinister Japanese engineers. Wth couldn’t they provide a fuel pressure test port like most other manufacturers on earth? I’d love to know what my pressure is at without all the bs of playing musical banjo fittings. I know damn well if I attempt it, I won’t have what I need, be dropping stuff, throwing a nutty.