P0171

My tech stream has not helped me much at all ...nothing to really reset wen I have a code or codes. It always wants to run a series of tests. That seem to be inconclusive..battling same code but cars getting proper gas mileage so more of nuisance.

 

Unless finances are critical, having Dr Prius for monitoring hybrid functions is a good idea for any Prius owner- I keep the adapter in the glove box and can check things when I am away from home.

I just looked at amazon for a seller that had the software on a cd/dvd (didn't want to deal with some unknown online download). Don't know of any differences in the cheap cables- the seller I used raised his price by over $20, so shop around. Ebay is also works but can take longer depending on where the seller is. I understand that there are usually fewer installation problems if you have a 32 bit windows operating system (I used Win7 pro 32 bit). Sometimes the 64 bit driver can be fiddly.

 

apparently their are issues w veci cables . the standard is iffy at best . or the adhering to the standard.. ive bought about 5 theyre cheap enough.. ones that do not work i return..

 

I am getting p0171 the last 100 miles . I am suspecting the same. In my current tank of gas as I had added duralube catalytic converter cleaner.

Just 100 miles ago I had p0113 and p103, but after cleaning dirty MAF and replacing air filter, I don't have those 2 codes. Just p0171

 

Upstream 02 possibly

 

That's on my list to check. First I will replace MAF sensor and see if that resolved this p0171. Just 100 miles ago I replaced the CAT and downstream O2 sensor. Had not replaced upstream O2 sensor.

 

I would say just clean the MAF first they don't really go bad that often unless you mess it up with the spray tube when you're trying to clean it there are parts that are inside of the plastic that you have to look carefully at the MAF and get the tube in there to clean it correctly You can also use a q-tip you'll be surprised at the dirt and blackness that comes off on your q-tip than just put it back in see what you got I have rarely replaced MAFs on the Toyota's just a cleaning generally does the trick.

 

I've seen a couple posts lately where somebody's MAF sensor inhaled a little leaf bit that got past the air filter (probably shaken off the air filter while someone was changing it) and led to a pretty stubborn P0171.

 

Are you sure the MAF is plugged in correctly (or the connector isn't damaged?).

What does the MAF sensor read under different conditions? What are short term and long term fuel trim numbers at idle and at cruise? What is upstream AF sensor voltage readings?

Here are som MAF readings from a known good car.

Posted via the PriusChat mobile app.

 

Today

Today was the 2nd attempt at cleaning. This time I made sure MAF wire that's inside is sprayed adequately as well as the amber bulb. Left it for 15 mins to dry before putting back in. Reset code by unplugging the battery. Driven 20 miles. So far no p0171. First time around after cleaning it took 50 miles for p0171 to show up.
(MAF is correctly connected to the connector)
One other variable was "bad" gas (I had put a catalytic cleaner in gas tanj) which may have clogged fuel injector. Now gas tank is almost empty. So tomorrow will fill it with just gas.

 

Cleaned MAF sensor. Reset code by disconnecting battery. After 40 miles, got p0171
Replaced MAF sensor with new Denso Sensor . Reset code by disconnecting battery. After 40 miles of driving got p0171 again

Since I replaced my CAT last week, I am asking the shop to check if there's an exhaust leak that's causing p0171. Car runs fine no jerky acceleration, etc. MPG is a little lower at 40mpg

After that my next step is to put replace upstream O2 sensor.

Any ideas / suggestions? No I do not have techstream or other tools to monitor data

 

No exhaust leaks were seen. CAT has been welded properly. Maybe next I need to check for vacuum leak or replace upstream O2 sensor.

 

<shrug> It's your money, you can spend it as you will.
You can fire the parts cannon if you want.

Here's a thread that reviews several scantool apps and devices.
https://priuschat.com/index.php?posts/3290690


I know that there's a whole bunch of confusing data coming from the scantool, but if you can understand it then that can point you in the correct direction.


Posted via the PriusChat mobile app.

 

Took the car to auto repair to do the diagnostics. They did a smoke test. He says there is no leak except he saw smoke near the valve cover gasket. This was replaced just 6 months ago. This Prius takes 1 quart oil between oil changes.
He is suggesting replacing the valve cover gasket!

MAF sensor he says is working fine

He does not think it's related to fuel pressure or fuel pump or dirty fuel injector or O2 sensor as he thinks those will set different codes

Mpg has dropped to 36mpg from what used to be >42mpg. Drives just fine.

Can't tell what's wrong. Since the mechanic it's ok to drive, I'll monitor next few 100 miles to see if code gets set again and how mpg is.

Any recommendation for fuel injector cleaner that works well with high mileage Prius? Any other ideas for resolving p0171

 

It COULD be a vacuum leak, but that would show up as high positive fuel trim numbers only at idle. At cruise and on acceleration fuel trims would be closer to 0.

What does the freeze frame data from the last P0171 code show?

Fuel that has high ethanol content would cause high fuel trims under all conditions, and likely P0171. Restricted injectors would cause the same thing - possibly misfire codes if one was bad enough.

Low fuel pressure would cause high fuel trims and P0171 - likely reduced performance under high load if it's bad enough.

A biased (bad) upstream A/F sensor can cause - high fuel trims and P0171 (or other codes).

What test was done to confirm that the MAF is reading correctly? I have known good MAF data under different conditions - but you would have to have a scantool to be able to check this.

Short form is data from the ECM should point a mechanic towards the next test that will prove or disprove a particular part or system is good or not.

Posted via the PriusChat mobile app.

 

Thanks for listing the possible reasons
I don't know what scan tool was used. I asked for all scan data and they declined.
I may still have a bit of "duralube cat cleaner" in my tank. Wondering if that had anything to do with getting the code ?

How easy is to check fuel pressure ? Is there a Schrader valve in 2007 Prius ? Now if fuel pressure is low , I guess I have to replace the fuel pump assembly. Are there good aftermarket ones?

What's the effective method to clean fuel injectors assuming there is a clog ?

I don't think there is any misfire now. There was when MAF and air filter was very dirty. Then I had performance issues, also very slow & jerky acceleration, misfiring. Now engine seems to run smooth.

 

No schraeder port on a Prius. You would need a gauge set that has the correct adapters to fit inline between the fuel rail and the supply line.

Really, you have to decide if you want to get a capable scantool (there's reviews at the top of the Technical Discussion forum) and educate yourself, or if you want to find a better shop.

Posted via the PriusChat mobile app.

 

Driven 120 miles after I took it to mechanic. No p0171 and mpg is 45mpg.

The mechanic who did the smoke test also had said he had to tighten the bolt in the intake, the part right under the MAF and he had said it MAY make a difference. I believe that's why I was getting p0171. I cannot tell how that bolt became loose because all I did was clean and then replace the MAF. But I guess somehow when I took the MAF out and put it back that bolt became loose. Because first I only got p0103 and p113. Only after I replaced air filter and cleaned MAF I started getting p0171

He tried to upsell replacing valve cover gasket which I had replaced 6 months ago and I don't think I need this.

 

It is not an up-sell if it is leaking, it needs to be replaced. If you do the job it needs to be done properly so it doesn't leak.