Post Reply 
 
Thread Rating:
  • 0 Votes - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
"Check Engine" Light On - P0171 - How bad is this?
Author Message
RebelScientist Offline
Member
***

Posts: 25
Joined: Feb 2008
Reputation: 0
Post: #1
"Check Engine" Light On - P0171 - How bad is this?
Hi Mike, Hi everyone. I've had EFIE running .2 v on Car for about a week and the CEL came onn. The car is Toyota Corrolla 98 with 4 wire 02 sensor. engine I4 so one pre cat. O2 sensor.

the code that it shows is P0171- which means "System Too Lean (Bank no. 1 ) " also code p0125 is up (Insufficient Coolant Temperature For Closed Loop Fuel Control )

The car runs fine. I haven't notticed any millage gains but the noise and viberation is lower. The fuel assist device is HHO Gas

my question is: How bad is this? if my car shows millage improvements, can I Ignore these codes? also, I need VA Emissions done by March, so would this effect the OBDII emission Inspection? thanks.
02-20-2008 02:55 PM
Find all posts by this user Quote this message in a reply
mike Offline
Senior Member
****

Posts: 2,020
Joined: Jul 2007
Reputation: 7
Post: #2
RE: "Check Engine" Light On - P0171 - How bad is this?
Your fuel mileage will be considerably worse if the computer is running in open loop. It will guess in the direction of too rich, always, when it thinks it doesn't have enough information.

Did you have the light on before you started your hho modifications? You might just need to replace the temperature sensor.

Also try lowering the EFIE to .100 to so, and work your way up from there.

You definitely want to get rid of those codes.

[Image: signature.gif]
Visit Our Documents Page
02-20-2008 03:12 PM
Visit this user's website Find all posts by this user Quote this message in a reply
RebelScientist Offline
Member
***

Posts: 25
Joined: Feb 2008
Reputation: 0
Post: #3
RE: "Check Engine" Light On - P0171 - How bad is this?
I dont think its running in open loop. the engine noise is different when efie is set on low and when set on high. when set to low voltage, the car sounds like when it didn't had efie OR when 02 sensor is disconectted(rich mixture). when set to high volts (.2) the car sounds alot silent (leaner).

the light turned on after the efie was connected.

if I turn off my EFIE device, the O2 sensor runs normal right? so if I leave it off for 2-3 cycles, the light should go away, unless its somethingelse.

are u sure about EFIE not alerting ECM about change in fuel consumption? I think that my ECM is freaking out because the fuel consumption has gone down so its sending these codes.
02-20-2008 08:28 PM
Find all posts by this user Quote this message in a reply
mike Offline
Senior Member
****

Posts: 2,020
Joined: Jul 2007
Reputation: 7
Post: #4
RE: "Check Engine" Light On - P0171 - How bad is this?
You are correct, if you turn the EFIE off, the sensor is connected directly to the computer, with no added voltage. So if the EFIE is causing the CEL, then it will go off again if the EFIE is off, assuming your computer doesn't require a reset.
In answer to your last question; What will make the computer think your sensor is on the fritz is if it gets data that's impossible from a functioning sensor. As long as it's getting readings that go low enough, and then gets switching to higher voltages (the range of these voltages is below .45 volts and above .45 volts), then the computer will be happy with the sensor, and will use it's data.

You might want to get some readings of your EFIE's test ports to ground as per How to Read Your EFIE, and see if your readings there are as expected.

Are you absolutely, 100% sure that you have the oxygen sensor signal wire, and that the EFIE green wire is connected to the sensor, and the white wire is connected to the computer?

[Image: signature.gif]
Visit Our Documents Page
02-20-2008 09:56 PM
Visit this user's website Find all posts by this user Quote this message in a reply
RebelScientist Offline
Member
***

Posts: 25
Joined: Feb 2008
Reputation: 0
Post: #5
RE: "Check Engine" Light On - P0171 - How bad is this?
Okay. I am sure about my connections and that the EFIE is working. I asume this by the sound my car makes under acceleration. My engine is built so that the exhaust Manifold is facing the driver and not the radiator. When its burning rich (which happenes when mY fuel effeiceint device is working or when O2 sensor is disconnected), I can hear a wet exahust sound through my exhaust system. when it burns normal, or lean, The sound is rather dry(if I can hear any).

when my EFIE is on and fuel efficient device (HHO) is connected, and EFIE is set to .15v, I hear wet sound. When its closer or on .20v, its starts to go away.
This tells me that my O2 and my EFIE is working. Computer is leaning out fuel.

But then I get these codes. I am not so worried about the p0125 but a little about p0171. why is my computer sending these codes? :question:maybe because computer is aware of fuel delivery change somehow?:question: and that a slight change in .45v (14.7:1) ratio is noticed and reported.

I have turned of the efie and the car is running back to orignal. just waiting to get that CEL to go down and then I'll take it for emissions.

I am thinking of passing the .2v mark to myabe .25v or higher on EFIE, to see how it does, thus ignoring the CEL for the next two years....... as long as milage are increased.

what do u think?
02-21-2008 09:50 AM
Find all posts by this user Quote this message in a reply
mike Offline
Senior Member
****

Posts: 2,020
Joined: Jul 2007
Reputation: 7
Post: #6
RE: "Check Engine" Light On - P0171 - How bad is this?
I don't think that your mileage increases will remain while the engine thinks there's a problem with the oxygens sensor readout. It should stop using it's data, and this will be bad for gas mileage. However, this is what I guess will happen. I don't know for sure, because I don't know precisely what's going on with your engine.

If it were my car, I would try to get a resolution to the engine light AND get my mileage increase too.

Did you get a CEL when the EFIE was set a lower settings, such as .100? If not, I'd go back to .1 and work up from there until you get the highest setting possible without a CEL and see what your mileage is then.

Another possibility: Are you absolutely sure that you hooked up the EFIE with the green wire towards the sensor and the white wire towards the computer? If hooked up backwards, the computer might report that the mix was too lean. The EFIE, hooked up correctly will make the computer think the mix is richer, so that it will lean it.

[Image: signature.gif]
Visit Our Documents Page
02-21-2008 11:20 AM
Visit this user's website Find all posts by this user Quote this message in a reply
RebelScientist Offline
Member
***

Posts: 25
Joined: Feb 2008
Reputation: 0
Post: #7
RE: "Check Engine" Light On - P0171 - How bad is this?
hmmm.... I see what you are saying..... Okay thanks, I'll go take a look if the connections are in the right way. Thanks

is there a sensor somewhere else in the engine that could detect the use of less gas?
02-21-2008 10:35 PM
Find all posts by this user Quote this message in a reply
mike Offline
Senior Member
****

Posts: 2,020
Joined: Jul 2007
Reputation: 7
Post: #8
RE: "Check Engine" Light On - P0171 - How bad is this?
The computer uses an array of sensors, including the IAT (Intake Air Temperature), MAP (Mass Air Flow), MAP (Manifold Absolute Pressure), as well as the oxygen sensor to determine the correct amount of gas to inject. It's only way of determining the result of the calculations though (that I am aware of) is the oxygen sensor.

I suppose that if the various sensors didn't add up in an expected way, it might trigger an error code in some way.

But I wouldn't look for the exotic reasons just yet. Most problems are resolved by double checking that the connections are made, and are made to the right wires. Verify that your power really has 12 volts, and that your ground really is connected to the battery's ground terminal. And that you really are on the oxygen sensor's signal wire. Check for shorts. Things like that. Check the reference "How to Read Your EFIE" (see link above), and make those checks. Make sure all of the readings are as expected.

Let me know what your find out.

[Image: signature.gif]
Visit Our Documents Page
02-21-2008 11:41 PM
Visit this user's website Find all posts by this user Quote this message in a reply
RebelScientist Offline
Member
***

Posts: 25
Joined: Feb 2008
Reputation: 0
Post: #9
RE: "Check Engine" Light On - P0171 - How bad is this?
Hey Mike, Yesss.... One of the wires came loose. I connected it back to make it a close loop. and the CEL goes right away. Big Grin

I have rechecked all the wires and they seem to be connected in order.

what way do u guys use to connect two wires togather? the best way is soldiering but for some reason, the soldier metal is not sticking to my O2 Wires. I am using electrical tape but it doesn't hold for long. and I can't hammer the wires cause my O2 sensor is still mounted. Any other Ideas?

I'll resume testing my EFIE device and milage after I get emissions done.
02-25-2008 11:05 AM
Find all posts by this user Quote this message in a reply
mike Offline
Senior Member
****

Posts: 2,020
Joined: Jul 2007
Reputation: 7
Post: #10
RE: "Check Engine" Light On - P0171 - How bad is this?
Yes, I have an idea. The wires down by the sensor are sometimes made of a lower grade stainless steel, in order to stand up to the heat of the sensor. In that case, they don't solder very well. I've never tried it, but you might be able to still solder there, but will need a hotter iron. That may not work either. You have probably already cut into the wire, so will have to reconnect anyway. In this case I would get some good crimp connectors. You can get them from the auto parts store. Lastly, I would get some heat shrink tubing. Your auto parts store should also have it. I wouldn't use the Radio Shack version, as it's not very heavy duty. If your auto parts store doesn't have the size you need, get it from an electrical supply house. Electrical tape will just melt that close to the exhaust pipe.

See if you can pick up the wires up above, near the ECU. If you have a wiring diagram, you can find the correct color of wire. You should be able to find it where the wiring harness plugs into the ECU. The wire there will always be tin plated copper, stranded wire, which will solder up nicely for you.

[Image: signature.gif]
Visit Our Documents Page
02-25-2008 06:19 PM
Visit this user's website Find all posts by this user Quote this message in a reply
Post Reply 


Forum Jump:


User(s) browsing this thread: 1 Guest(s)