P0171 what to try..

After owning my truck for over 2 years it finally decided to throw me a cel yesterday, ran it on my scanguage and it came back the p0171 (lean condition bank1). Went through the search and some say clean maf, replace o2 sensor, check hoses for vacuum leaks etc.
My plan is to re-clean the maf again, did it about a year ago. I think the sensor may be the factory one, if so it has almost 220k on it. Gonna order one just in case. I looked at all my hoses there all plugged in and no leaks i can find.

Is there anything else I can check in my driveway that I missed? I cleared it and it came back within 30 miles. runs fine like usual just have the annoying light.

Thanks guys

 

it appears that you have checked the obvious... have you taken the air tube off the throttle body to MAF and really looked at it close. They have a tendancy to crack at the expansion bellows. Difficult to see with it on the truck. If there is a crack and you need to replace it in certain years of first gens Toyota has a differernt air tube that requires a few more hoses to make it work with your truck. Hopefully the parts tech recognizes this and orders them too. Nothing more frustrating than only getting half the parts.

dont clear the code... you will erase the information that either you or the tech is going to need to diagnose this condition.

This is fixable in the driveway with the proper scanner, some tools and time, unfortuatly your scanguage isnt going to help. You are going to need a OBDII scanner that displys live data, specifically short and long terms fuel trims.

 

I would recommend replacing your MAF with that many miles. I've talked with a few 5VZ owners that said doing this restored a fair amount of power

 

I have a scanner as well. I think i may have discovered the issue, i found a vacuum hose that goes from the upper intake to the charcoal canister that was split at the metal port above the intake. Im gonna get some new hose tomm and replace it. Hopefully that clears up the problem.

 

I bought a 2001 Ext. cab V6 Manual Transmission with 180k recently and had this problem as well. It would die when coasting to idle, rough idle. Started diagnosing it and found: 1. Airbox tube was cracked, apparently the previous owner tried repairing it with epoxy. Airbox replaced and cleaned MAF sensor, fixed the dying and rough idle issue, purred like a kitten. Thought it was fixed but it would throw the p0171 code after about 20 miles of driving. Checked for vacuum leaks, checked 02 sensors, and replaced the PCV valve with still no luck. Every 18-20 miles, it would throw the code back despite the motor running perfectly.

Replaced the fuel filter and added a can of sea foam last night and now have 60 miles on it with no code. It starts easier, doesn't hesitate, and even idles smoother than my 2016 Double cab now. It makes sense to me, lean condition means too much air not enough fuel. The computer is trying to compensate for starving it of fuel, so it throws the code.

 

I replaced the vacuum hose and so far after 2 days of driving no light. Guess it doesnt take much of a air leak to toss a lean code. It was prob a 1/8 inch split right on the flared part of the metal tube was it. Hopefully its fixed now.

 

An 1/8in crack is plenty to cause that.

 

Thought I had it fixed... but its back. Paid a local independent tech to plug their computer in and diagnose it so I could quit throwing parts at it. They told me it was the water temp. sensor that was bad. It made sense to me, but I had a feeling about it. Replaced the sensor, cleared the code, and just like clockwork, 30 miles later the check engine light comes on. Scan gauge says it's another P0171.

We have valve cover gaskets and timing belt parts coming in next week, perhaps when I take all of that apart I'll accidentally fix it or find the obvious problem.
Engine runs excellent, no hesitation, rough idle, etc...

Anyone else have any ideas? I'm about to lose my mind.

 

I had ordered me a new o2 sensor because both my o2 sensors are factory Toyota. 219k miles on them. I fixed my p0171 with a new vacuum hose but since I had the new sensor I threw it in (upstream). Oddly 30 miles after I get a p0420. Cleared it and 30 more it comes back. I pulled the live data and sure enough the rear o2 is switching voltage just like the upstream. The cat was replaced less than 10k miles ago. No clue if it’s cause one sensor is new and other is 20 years old or what. Kinda aggravated

 

Anyone else ran into this problem after changing out only 1 o2 sensor? I suppose it could be because the cat is a cheaper aftermarket one. But seems odd it tossed the p0420 right after replacing the front o2?

 

Following, as I have been trying to figure out the same flippin code.

 

What sensor did you put in? If it wasnt a Denso sensor, then that's your problem. These trucks only run right on Denso sensors, and there are a lot of fake ones on places like ebay.

 

P0171 or p0420?

Unfortunately I've battled both, p0171 is usually vacuum leak related and p0420 is usually a bad cat. Except in OPs case since it happened right after he installed a new sensor, it's either a bad aftermarket sensor or a leak before the sensor

 

I had the same code. Replaced the vacuum switching valve and that fixed it right away.

 

Denso from rockauto. The sensor I pulled out was oem. The aftercat sensor is oem still as well. I replaced the before cat o2. It’s functioning as it should. The oem after cat one is the one that came in the truck. It has almost 220k. I don’t know if it went wacky or what. There’s no exhaust leaks at all.

 

P0171
I had the shop do a smoke test, and nothing.

I am thinking it might be the brake booster. Every once in a while I get a hard to brake feeling when I have to slam (or try to slam) on the brakes. Also, when holding down the brake pedal, it has a slight hissing sound. Not always though.

 

I’ve heard in rare cases the fuel pump and or fuel filter can toss the 0171. Mine turned out to be a simple fix thankfully

 

Ugh, my 06 Corolla had a recurring P0171 code. What a pain. I finally got annoyed and tired of dumping money into a 1500 dollar car. After replacing my maf and 02 sensors took it to a shop. They told me a bad 02 sensor. Never figured out what was wrong with it.

 

I was thinking fuel filter as another possible cause. It was replaced about a year ago.

 

Just a little update I went back out and used a light this time. I thought I could see a tiny opening around the new o2 gasket. The nuts holding on the sensor are pretty rusty they had somehow loosened up a bit. I removed the sensor and put a tiny amount of rtv red around the gasket and tightened the nuts tight as I could. One began to strip sadly. But there both tight. I’ll clear it tomm and see what that does. If anything