P0171 CEL in 5th Gen?

[MSinDC]

Hey guys,

My '14 threw this code - P0171 Bank 1 system too lean - a couple weeks ago about 5 miles after filling up at a gas station during a road trip (tank was about half empty when I filled it up). Not saying that it was bad gas, but the fact that the CEL came on that close from filling up made me suspicious.

After utilizing our site's fine search function, I've learned that this code is usually associated with either the A/F sensor or possibly the MAF sensor, but nowhere have I seen anyone mention the possibility of bad gas initiating this code. Also, it appears I'm the only 5th gen that has gotten this code (or at least posted about it). I only really saw one 4th gen that had thrown it (pretty much all were 3rd gens).

Anyway, initially thinking it was bad gas and not really having any option to stop I continued (mainly because the truck has never offered any signs of mechanical trouble). After about 3 days, the CEL went off by itself. Great, I thought, must have been bad gas (filled up with premium the subsequent tank), but the CEL came back on a couple of days later. To keep it somewhat short, the CEL has been coming on and off ever since the first incident, yet the truck has shown no signs of a problem.

Anyone have any thoughts? Next time it comes on I'll take it in (still under warranty), I just haven't been able to make it to the dealership yet. Just curious if any of you shadetree guys have any bright ideas as to what it could be.

Thanks,
Turner

 

[jicko]

Take a pic when the CEL come on, and bring the truck into for warranty.

 

[bloodninja]

CEL codes are stored in the vehicle's onboard system. You don't need the light to be on for the code to be pulled. Bring it in under warranty regardless and have them check it out.

 

[SR5Bart]

CEL codes are stored in the vehicle's onboard system. You don't need the light to be on for the code to be pulled. Bring it in under warranty regardless and have them check it out.

This^^^^

 

[MSinDC]

CEL codes are stored in the vehicle's onboard system. You don't need the light to be on for the code to be pulled. Bring it in under warranty regardless and have them check it out.

Thanks, any idea whether the codes are stored even after you clear it? I may or may not have cleared it because I couldn't deal with 2 orange lights and a blinking green light on a long night drive I had. Right now I'm just waiting for it to come back on to take it in b/c I thought I had lost the history when I cleared it.

 

[bloodninja]

Thanks, any idea whether the codes are stored even after you clear it? I may or may not have cleared it because I couldn't deal with 2 orange lights and a blinking green light on a long night drive I had. Right now I'm just waiting for it to come back on to take it in b/c I thought I had lost the history when I cleared it.

If you actually cleared the codes by means of an OBDII reader or the like, then yes, you will have reset the Emissions Readiness Monitors as well as any stored codes. If that's what you've done, then the dealership will have nothing to go on as far as pulling codes, but you still know what the code WAS, so you should have no problem letting the service department know what it WAS, so they can go from there.

 

[MSinDC]

If you actually cleared the codes by means of an OBDII reader or the like, then yes, you will have reset the Emissions Readiness Monitors as well as any stored codes. If that's what you've done, then the dealership will have nothing to go on as far as pulling codes, but you still know what the code WAS, so you should have no problem letting the service department know what it WAS, so they can go from there.

Yup that's what I figured. Thanks

 

[Lester Lugnut]

My 9.5 yr. old 2006 Avalon threw a set of P0172/P0175 codes right after turning 200,000 mile about a month ago. Problem is opposite of yours - too rich. Both banks.

I don't have a scanner that reads fuel trim, so I researched and found the problem to most likely be a bad MAF(mass air flow) sensor. On that engine the MAF sensor fits down inside the air flow circuit between the air filter and TB(throttle body). Likely similar on the 5th Gen 4Runner.

The MAF sensor on the Toyota's I've looked at have a couple of sets of platinum wires as part of the MAF circuit. These measure air and communicate back to a microprocessor with info that helps to control air/fuel ratio. If these platinum wires become dirty the MAF can over-read and skew things up. I had nothing to lose by attempting to clean the MAF.

Disconnect elect. connection - remove 2 small Phillips screws and out comes the MAF sensor.

Sprayed both areas on the MAF sensor that have platinum wires with CRC Mass Air Flow Sensor Cleaner. The prevailing wisdom tells one not to touch these wires, so I have always followed that advise. Let the MAF sensor air dry for about 30 min - reinstall and while I was at it changed air filter as well.
Cleared codes with my $50 Actron code reader and fired up engine.

Have put approx. 1100 miles on it since this work and no CHECK light.

A few days before the CHECK light came on I noticed bad mpg on a dash display that's part of the car. Right after that I also noticed sluggish acceleration when coming off a stop and then the CHECK light came on.

It would be my guess you may be getting better mpg because you're running lean. I'm not sure that a dirty MAF sensor could do the inverse and throw a lean code.

A member of this forum once posted the FSM(factory service manual) for a 2010 4 Runner. I went thru it and could not locate OBD-Codes. Here are the possibilities listed from an '05 Tacoma FSM for code P0171. I've read the causes for P0171/P0174 - P0172/P0175 in many manuals and see pretty much the same thing in all of them:

Air induction system
• Injector blockage
• Mass Air Flow (MAF) meter
• Engine Coolant Temperature (ECT) sensor
• Fuel pressure
• Gas leakage from exhaust system
• Open or short in A/F sensor (bank 1, 2 sensor 1) circuit
• A/F sensor (bank 1, 2 sensor 1)
• A/F sensor heater (bank 1, 2 sensor 1)
• A/F sensor heater relay
• A/F sensor heater and A/F sensor heater relay circuits
• PCV valve and hose
• PCV hose connections
• ECM


Something tells me your P0171 code will return. You'll then be able to get the dealer to look at it.

 

[MSinDC]

Just wanted to close the loop on this for future searches - CEL returned, so I took it to the dealer on Friday. They diagnosed it as a faulty fuel pump and replaced it.

Very strange since I never had any indication (other than the CEL) that anything was wrong with the truck.