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Discussion Starter #1
This is the third time that I remove the ground on the battery to erase
the fault egine light.
I have this miniscaner that works grate it gives me an error P0171.
I tried the gas cap but stil the same.
On the Toyota manual it says system too lean.
Anyone of you came across this problem.
peter11742
 

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Discussion Starter #3
Thanks for the reply.
I have a question for you what is the MAP sensor and where is located.
petrer11742
 

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P0171

Under the engine air filter you will see a small probe coming in from the front side. This is a mass air flow (and temperature) sensor. It (and the throttle butterfly further down) can both be cleaned, exercising the appropriate cautions.

It is not unusual for Prius to need its butterfly cleaned of soot.

If Prius also has a manifold air pressure sensor, it is not known to me. Hoping that DanMan has another comment on that.

DAS
 

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Discussion Starter #5
Thanks tochatihu
I looked the MAP probe is clean like new.
I looked the throttle is very clean.
I used compressed air and I saw nothing comming as a debris.
I looked all the vacuum hoses they are in perfect condition.
I think I must make some measurment to see if I can spot somthing wrong.
The car has 73000 miles most highway.
peter11742
 

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Re: P0171

tochatihu said:
If Prius also has a manifold air pressure sensor, it is not known to me. Hoping that DanMan has another comment on that.

DAS
Repair manual for 2004 mentions it in a Part and System Name List at the beginning of the SFI section, but only as a glossery entry. Not mentioned anywhere else.
Lots of stuff on the evap vacuum stuff though, including pressure sensors. Also the way the 200-2003 handles exhaust emissions control, a leak may be from there causing false O2 readings.
 

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Discussion Starter #7
Thanks DanMan32
I have the 2001 service manual and it says at the end of tree pages check list the the error P0171 is fuel starvation.
I will change the fuel filter.
I updated the miniscaner's software to version 7 and I can see the o2
sensor the air mas the injectors the spark plugs and the throttel position among other things.
I run out of luck at this time.
 

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Fuel filter?

Both the fuel filter and pump are integral to the fuel tank assembly, which is an expensive part. Is there a way to confirm fuel supply to the injectors (other than the milliseconds open time that you are seeing with the miniscanner)?

In TSB EG011-03, the replacement of the FT assembly is sometimes required, but before that, the fuel pump relay. Is it also possible in this case that this relay could be at fault?

I am not certain that it could be, because the typical DTC leading to this DTC is P3191.

This TSB and the others are posted in the files section of the Yahoo! toyota-prius-sat1 group. One must join that to read the files.

DAS
 

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Just a guess...

If it turns out that the problem is fuel pump-related, I think there was a recall on older Prius's a couple of years ago where the fuel tank and pump were replaced under warranty. I seem to recall having that done on our 2002, but my memory is a little fuzzy on this. I don't think there were any error codes on our car; and I believe that the replacement was done during one of the routine maintenance procedures.

You might want to see if this recall was done on your car.
 

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Discussion Starter #10
Thanks for the reply Phoenix
I looked all my records but I did not find anything with the fuel pump or the fuel tank.
The car works ok except it get's the engine light and the code P0171.
The code is starvation of fuel and is the worse to fix.
The car is year 2001.
 

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Discussion Starter #11
I have a question for all.
I saw a product that is made by chevron, techron 6740-12.
This suppose to clean the injectors and the intake valves.
Is it good for the prius or I will create more trouble.
Thanks
peter11742
 

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going to the cleaners

On various Prius groups I have read favorable reports about Techron, but never used it myself.

At least some Toyota shops use BG products for cleaning the air and fuel induction systems. This I did have done once, at 60k mles.

The only area of Prius that certainly needs periodic cleaning is the throttle butterfly and its environs, which does get sooty.

The injectors and intake valves may well require less of this type of maintenance than comparable gas-only vehicles. Other than the butterfly thing, this is not an area that I get very excited about.

Peter, if you have good reason to believe that the fuel filter is clogged, some suitable cleaning solvent into the tank might be worth trying before a complete fuel tank assembly.

DAS
 

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Discussion Starter #13
Thanks tochatihu.
I will try for a while the Techron and take it from there.
As far the throtlle is any way mechanically to see that behaves good.
I tried open and close from the side spring and always works.
peter11742
 

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is it the pedal?

peter11742 said:
Thanks tochatihu.
...
As far the throtlle is any way mechanically to see that behaves good.
...
peter11742
Not really, the best is to swap in a different one. As it happens, I have rebuilt these before, but now in the process of turning the 'business' over to another fellow. Business has been slow!

P1120 is DTC for bad accel pedal function, but apparently that code does not always appear.

One could always try 'pumping' the pedal an absurd number of times (like 30) when the car is off. The problem is noisy potentiometers, like a scratchy volume control in a radio. The real way to fix is to cut it open and really clean them up.

Seems that you have several other issues here to consider, before focusing exclusively on the accel pedal. Please keep us informed.

DAS
 

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Discussion Starter #15
Thanks tochatihu.
The accelerator pedal was replaced on this car under warranty.
You remind me the old days with my 1985 audi 5000 s.
I never had an idea that I have to open the buttrfly pot on the prius.
From 1 to 10 how difficult is to take it in pieces and clean it and having good mechanical ability and tools how long it takes in hours.
I have no warranty and the parts are expensive.
I may try to do it if you tell me that will eliviate my p0171 problem.
The p0171 problem is the same as the audi's where was cuting out of power due to clogged fuel pump.
Your information is always wellcome you have trementus knowledge on
prius problems and you are good help.
Any idea what is the cost of the butterfly mechanism I am going to get familiar so when my 2004 prius will give me troubles I will be ready.
peter11742
 

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the butterfly effect

Accel pedal was replaced? From that, I imagine that your VIN ends with a number lower than 45000.

Cleaning the throttle butterfly is not difficult. Instructions are available in the 'more technical' internet groups. Disassembly is not required, but one can do a better job by unbolting the entire assembly from the intake manifold. Aside from the tubings and electrical connectors, there are two (engine) coolant lines to disconnect. Those can be plugged with bolts wrapped with electrical tape.

It is not common for the throttle control assembly to need replacement, but there have been a few. I would guess price in the $200-400 range.

DAS
 

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Discussion Starter #17
Thanks tochatihu
You advise is valuable.
I will wait for the dechron to work for a while and I will keep an eye on the problem.
peter11742
 

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Just remember, the Techron is a fuel additive, so it won't do anything to the air path before the injectors. Well, some will get before the injectors in the manifold, since because of the akinson/miller cycle, some fueled air gets pushed back into the manifold.
 

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Iron butterfly (steel, actually)

I take DanMan's statement as suggesting that a little cleanup around the butterfly might still be to your advantage, even with the fuel system cleaner in use.

DAS
 

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Discussion Starter #20
Thank you both.
I am not so sure what you mean around the butterfly.
I am thinking around the perimeter of the butterfly that is the only place that I see not clean the rest is very clean looking.
what detergent agent you use I prefaire a good brand and your procedure if you have one.
Thanks
Peter11742
 
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