So my CEL is lit and I get these Codes P0171, and P0174, running lean...

Before starting this thread I searched many for clues. Based on those I have done the following with codes still tripping:

• New fuel filter
• New PCV valve
• New gas cap
• Cleaned MAF sensor
• Clean air filter
• In fuel injector.fuel system cleaner (Berryman) in the tank.
• All Motorcraft parts, no knock offs

The truck runs perfect, idles smooth, power is spot on. Only 60K miles and Is in perfect shape other than the dam CEL I have spent a week trying to clear.

My K&N ritual is solid, I have 2, when I clean one I let it dry for a couple of days, then oil LIGHTLY, then in the box it goes for until 6K of miles rolls. Next cheap step is to throw in a paper filter but with $100. already in K&N's I hate this move.

I know many talk of O2 sensors. Out of sheer desperation, I was about to just replace all 4 but after inspecting their locations, the front bank 1 connector looks inaccessible with out dropping the exhaust from the manifold, which I don't want to get into.

Any insight on this will be greatly appreciated.

Thanks,
Bill

 

Seems you are on the right track. I was told to replace mine (by the shop) when I received those codes.

http://www.obd-codes.com/p0171

 

It's not the 02's, save your money on that one.

Those codes are an air leak AFTER the MAF. Check any and all hoses that have vacuum. Brake booster hose can do it too. Check by the battery on the firewall there is a T and a line that goes to the resivour (sp?), could be there or even the res it self could be cracked.

Take a look at the intake tube from the air cleaner to the throttle body, make sure it is tight and no tears or cracks in it.

Also if it has a composite plenum, it could be cracked or bad intake gaskets.

Just throwing a few suggestions out, hope you find it.

Good luck

 

Thanks!

I checked all the tubing I could and it all looks good.

Guess I have to wave the flag and let the shop try to pin point it.

 

Take it to a muffler shop and have them replace the front two 02's. If it was unmetered air after the MAF it would idle rough and or hesitate. The rear two 02's are fine or you would get P0420, P0430 codes.

 

Good advice,

thanks Bob.

 

Lean codes and 0420/0430 codes are seldom caused by bad O2 sensors. The sensors are REPORTING on a problem.

 

about 18 months ago I had the same P0174, P0174 codes and in knowing every thing else was in perfect condition I replaced the forward 02's and cleared the codes and the codes never came back. The 02 sensor's can and do suddenly go out..EzraF has replaced and cleaned every thing up to the 02's. They are the next inline. If they do not fix the CEL then I would look at the injectors.

 

Correct! For the CM to report the 420/430 DTC's. The sensors must all be tested and shown to be reliable before the Catalyst Monitor can be called by the Executive. So, another (different) DTC would prioritize. Perhaps a low O2 DTC, such as 133, 153, -something like that.

For the 171/174 DTC's, the Fuel Monitor runs all the time that the engine is running. Although the monitor is running, in Open Loop no adjustments are made to the fueling trims. When the Entry Conditions are met the fuel monitor checks that the fuel trims have not exceeded their limits, which CAN indicate a deterioration in the HO2S sensors, or perhaps an intake or fuel pressure fault. So an O2 fault IS possible, -it just doesn't happen allot. Usually and 80 or 90% of the time, it's the PCV system. And almost always pin holes in the line or elbow back by the firewall. Don't get me wrong, it could be something else. Like the IAT grommet or just a loose intake tube, IAC bypass, MAF o-ring, etc...

It's a sure bet the O2's are bad when you receive both lean and rich DTC's at the same bank lol. - It's happens!

You'll know it's the fuel pressure reg if the engine has a hard time starting. - Either cold start or @ operating temp. But, most scenarios follow rich DTC's, over pressuring the rail, weak injectors, -miss firing is a common cause for rich DTC's. What does that have to do with lean DTC's ? Well, running rich can smoke the O2's fairly quick. -Making they're operation unreliable. So if a problem existed in the past, -it may be a cause of what's going on now.

 

This is the route I'm going now. Ordered the 2 front o2 sensors (Mototrcraft) off Amazon, which saved me $60. off my local parts store.

I'm gonna suck it up and do it myself, figured digging into the passenger side was better than paying my shop $375. to do it.

Thanks for all the info everybody.

 

I agree. Specially with both banks testing positive for lean, - and at the same time. If the OP would post EXACT idle rpms @ operating temp in park, it would be much easier to diagnose. But hey, sounds like he has plan set in mind. Maybe we'll get to see how that pans out for him jgger.

 

^^^Probably 2 shiney new O2's and a SEL.

OP post what the fix is, just curious.

 

Checked all the lines and connections after the MAF and everything looked good, short of a smoke test, I could not find any breaches.

Idles in park around 700-750 RPM's and idles smooth at normal operating temp. Power has never been better after cleaning the MAF.

Bought the front O2 sensors(Motorcraft) cheap off Amazon, but have not switched um yet. The passenger side sensor looks like its gonna be a real pain to get too.

Many thanks for all the valuable input. I'm hell bent on fixing this nuisance.

 

What the heck is a SEL ?

 

CEL? SES? (Check engine light - service engine soon light)