CEL CODE P0171

New here and need help. Just bought 99 Toy PreRunner,155 k,3.4,auto. Got CEL, P0171 and replaced about everything I could. Both 02 sensors, plugs, wires, fuel filter, stock air filter, cleaned MAF, checked all vacuum lines. Reset by battery disconnect. Good for about 5 miles and light returns. Truck runs great, but I have to let it warm up a little in the morning otherwise it will hesitate and hardly pick up any speed. Need help not BS.

 

Thanks, never even thought about that. Will check this weekend.

 

Changed engine coolant temp sensor this morning, still have all original problems. I am lost as what to try next.

 

Did you clear the trouble codes?

If the repairs got the problem the computer would clear itself but it will take a number of drive cycles to do it. If it didn't the TC will just come back.

 

No did not clear the code. Did drive about 10 miles after repair and 20 miles today, but did notice today there was no hesitation after start up and driving without extended warm up.
Are you saying to disconnect battery cable to clear the code?

 

yeah,.......disconnect the battery for a half hour and then drive and see if cel comes back on.

 

Or get yourself one of these: An essential item in your automotive tool box it reads, interprets and resets TC's on all OBD-II vehicles made since 1995 or so. Price to buy is about 1/2 what most shops will charge for the same service so it starts paying for itself immediately.

The only TC's it doesn't interpret correctly are mfr specific ones but if you Google it along with the mfr. you'll find a dictionary. A great feature for those of us in bend-over states is that it tells you if/when your computer is ready for emissions inspection.

I think ScanGuage II (if you have one) does it too but I'm not sure, especially about the interpreting of codes part.

 

Ok here is the lastest, did the battery disconnect and it lasted about 3 miles and the light came back on. Truck was running great at least. I love the truck but i am losing faith about being a Toyota owner again, (Had one back in1990, no problems). The last post said to buy a scan gauge to clear the code, if this will work i am willing to take a chance. But am afraid i might need the money for another suggested part even though the last one did fix the hesitation. So my question is now what?

 

I agree the battery pull thing would reset the light just as good as a scan gauge but I disagree it wouldn't be useful.

About now, you might be assuming the TC is the same one: it may have changed. Or the ONLY one: there could easily be two or more 'cause the thing that's broke is making multiple parameters go out of tolerance. If you knew the whole story would be easier to troubleshoot.

And don't lose faith in Toyota 'cause of this...cars' emission controls have gotten a lot more complicated with federal and state mandated rules to highlight relatively minor failures of things we used to drive broke all the time.

 

Its definitely vacuum leak either near PCV valve or that Evap hose that goes to throttle body.
judging from your description its a hair like crack. so
Remove evap hose completely and check for cracks
Remove PCV hose, PCV valve and grommet check all ..

 

Thanks all, I did replace the PCV already and I will recheck all vacuum lines. An old shade tree told me to start the engine and use propane gas around all the lines because if theres a leak the engine will rev. Sounds reasonable, and I will revisit my local Autozone for a re-scan to see if the same code comes up. What do you guy`s think about the propane? Or is there another way other than visual?

 

Please dont use propane, its too cold for attending funerals.

Starter fluid is your choice. It tends not to explode on ignition.
However, I still would check evap hose and one going to PCV. Also check that air tube (between MAF and throtle). It has to be very small crack somewhere or something is not seated right. What did you work on it before that happened?.

 

MAF sensor could be dirty but leaks downstream of the MAF also could be cause

 

The fault code that you have posted seems to suggest an issue on one side of the engine only. I would think that the MAF and anything before the intake manifold should be okay. You already replaced the o2 sensors. I would be looking real hard at the intake gasket on that side of the motor. Another thing that it could be is a bad fuel injector. It happened to my boss on his 3.4 4runner at around 150K. Not sure what fault codes he had. How hard is it to swap the injectors side to side? If it's easy to do, you might try it and see if the fault code moves to the other side of the motor.

 

Answer to the above posts:
I bought the truck about 2 months ago. I got a few miles down the road as a proud owner and the check light came on. I thought nothing about it and I knew I would have to spend a few bucks to get it into shape. So here is a list of what I replaced and done.
1) Replace both upstream and downstream o2 sensors.
2) Replaced fuel filter.
3) Plugs and wires.
4) Replaced ECT sensor.
5) Replaced PCV valve.
6) Cleaned MAF (twice)
7) Use only Chevron 91 oct.
8) 1 can of Seafoam.
9) Has new airfilter (paper)
10) Checked all vacuum lines, (today I will run and check with starting fluid)
11) Prayed that damn light would stay off after evey fix.

 

Could be the MAF's just shot shot and a new one is in order...don't know how expensive it is. You may not like to hear it but sometimes you just gotta take it in and let the shop look at it as they have the diagnostics to help keep the swap-it-and-see costs down.

But then, many times that's all they're left with too...

Good luck. With winter coming up I know I want to make sure my truck's running smooth too.