Check Engine Light Code P0171

[mr t]

Good evening everyone,

I would like to know if anyone else has encountered the above code.
It means that I am running too lean.

The light came on acouple of days ago while driving in Boulder, CO [5500ft].
My milage is 1160 and this is the first time that I have had a check engine light problem.

Around 850 miles I installed a ITG intake exhaust and an Arqray SS twin muffler.

My routine dealer visit was at 1023 miles. At that time they reset my ECU as per TSB dated 3/06 for stall problems of which I have never had to that point.

Now it looks like another trip to my dealer to see what they can do for my situation.

Does anyone know why this has happened and how to solve the problem so It doesn't happen again?

Will my dealed say it's because of the ITG intake, so it is not covered by the warranty?

There was one instance after my 1K service that the car did stutter at idle, corrected by a slight touch of the gas to keep it from stalling.

Thanks for your opinions.

Best regards,

mr t
Nederland, CO [ 8500ft ]

[MattG]

Just curious, did the CEL come on during WOT driving? If the ECU is running in open loop mode off of predefined maps, and if you significantly increase the airflow, it seems possible that you could be running leaner than usual. I think the dealer will almost certainly blame your intake and exhaust modifications and not agree to do anything more than reset the CEL.

[RopaS2]

Originally Posted by mr t

Good evening everyone,

I would like to know if anyone else has encountered the above code. It means that I am running too lean.

This is a Federally-mandated OBDII code, and it can be caused by a relatively wide variety of malfunctions.

I believe the most likely cause is a vacuum leak somewhere downstream of the airflow measuring device. Other possible causes are problems in the EGR system or a leak in the evaporative recovery system.

Will my dealed say it's because of the ITG intake, so it is not covered by the warranty?

They might, and I believe they would be on relatively firm ground in doing so.

[TimMullen]

From the Service Manual (everyone should go to the Lotus web site and download the manuals for $25.)

Lotus Service Notes Section EMP Page 20



Fuel Control System Too Lean Or Rich
P0171
P0172
P0171 System Too Lean
P0172 System Too Rich

Description
The oxygen sensor sends a signal to the ECU corresponding to the exhaust gas oxygen content enabling the ECU to maintain a 14.7:1 air/fuel ratio under normal driving conditions. The ECU can make fuel corrections of ± 17% to the calculated fuel demand. If the ECU determines a rich condition exists (oxygen sensor above 0.450mV), it will decrease the calculated fuel demand to maintain a 14.7:1 ratio. If the ECU determines a lean condition exists (oxygen sensor below 0.450mV), it will increase the calculated fuel demand to maintain a 14.7:1 ratio.

Enable Criteria

• Fuel Trim condition enabled
• Closed loop fuelling enabled
• Engine speed > 1100 rpm
• MAF > 6 g/sec
• Engine load < 70 %
• Altitude < 8000 ft (2438 m), Baro > 756 mbar
• Inlet air temperature > -10°C (14°F)

Disable Criteria
P0106, P0107, P0108 – Baro sensor faults
P0111, P0112, P0113 – Air Intake Sensor faults
P0131, P0132, P0133, P0134, P0135 – Oxygen sensor faults
P0300, P0301, P0302, P0303, P0304 – Misfire faults
P0441, P0442, P0443, P0447, P0448, P0450, P0451, P0455, P0456 – EVAP faults
Monitor: Continuous

Malfunction Criteria

P0171
This code is set when the calculated fuel demand has been increased to its maximum limit of 17% and the system still cannot maintain an air/fuel ratio of 14.7:1 under normal driving conditions.

Potential failure modes:

• Fuel Pressure too low
• Air leak in system
• Water in fuel
• Exhaust leak / crack before front oxygen sensor
• Injector fault
• Sensor connector and wiring for signs of corrosion or loose connections

P0172
This code is set when the calculated fuel demand has been decreased to its minimum limit of -17% and the system still cannot maintain an air/fuel ratio of 14.7:1 under normal driving conditions.

Potential failure modes:

• Fuel Pressure too high
• Leaking fuel injector
• Restriction in the exhaust system or air intake / filter
• Erratic throttle position sensor

Notes:
The MIL will be illuminated if the fault is present for 2 consecutive trips.
Further information on the sensor may be found inToyota 1ZZ-FE, 2ZZ-GE manual RM733E (B120T0327J) pages DI-67 to DI-72.


I'd be looking for any loose connections frim installing the air intake and/or leaks.

[evomind]

isnt 14.7 running rather rich??

[Illusive]

Originally Posted by mr t

Good evening everyone,

I would like to know if anyone else has encountered the above code.
It means that I am running too lean.

The light came on acouple of days ago while driving in Boulder, CO [5500ft].
My milage is 1160 and this is the first time that I have had a check engine light problem.

Around 850 miles I installed a ITG intake exhaust and an Arqray SS twin muffler.

My routine dealer visit was at 1023 miles. At that time they reset my ECU as per TSB dated 3/06 for stall problems of which I have never had to that point.

Now it looks like another trip to my dealer to see what they can do for my situation.

Does anyone know why this has happened and how to solve the problem so It doesn't happen again?

Will my dealed say it's because of the ITG intake, so it is not covered by the warranty?

There was one instance after my 1K service that the car did stutter at idle, corrected by a slight touch of the gas to keep it from stalling.

Thanks for your opinions.

Best regards,

mr t
Nederland, CO [ 8500ft ]

Originally Posted by Illusive

looks like the maf isn't positioned properly in the intake tract, and causing the evap cel.

I'll go a bit more into detail on what I meant. I didn't mean the maf was installed incorrectly, but the mounting flange isn't welded properly onto the intake pipe.

The celica community went through these same problems with the first generation intakes that were made.

AEM ended up having to have each mounting flange for the maf's to be mounted via machine, rather than by hand, this helped reduce the variance from intake to intake and stopped nearly all the CEL's their intakes were causing.

Simply put, if its off center(the maf or mounting flange), or the rotated a bit so that it doesn't get correct air flow across it, or the section of the pipe is too turbulent the maf wont read airflow correctly. Not everyone who purchases this intake or any other intakes will have the same problem, only when the flange is just a hare off its mark will cause the CEL.

There is a fix however, I can't take credit for it, but you can remove the fins in the stock intake tract, designed to provide proper airflow across the maf and incorporate that into the intake. This will eliminate your cell.

Worst case I'd contact ITG, and request a new Intake, since yours is causing the CEL, and it seems others are not.

[Illusive]

Originally Posted by evomind

isnt 14.7 running rather rich??

thats actually rather lean, if thats the air/fuel read out pre-cat.

13.0-13.5 is generally as far as most tuners go for n/a power under wot full load conditions.

off throttle/ low load can get up to 15.0's and still be okay for fuel economy.

It also depends on how much ignition your running too and what your knock levels are like.

[MattG]

Interesting info, Illusive! Nice to have the Celica community's experience with this motor to help us out here.

[qball]

I assume the fins go between the filter and the MAF sensor?

[Illusive]

Originally Posted by qball

I assume the fins go between the filter and the MAF sensor?

yes

best spot is about an inch before the maf.

[Beanie]

Someone in a thread about making your own intake claimed that there are no fins in the Elise intake tube. http://www.elisetalk.com/forums/showthread.php?t=12470

Lean condition could be any number of things, but I suspect the intake, too, since it's aftermarket and probably smaller diameter than stock (to make it run leaner on purpose for more power). Like Illusive said, if something is off by just a little bit in the MAF mount, that could do it. The MAF could be too low in the tube or crooked.

Another thing to check for is an air leak. First place to look is the intake, since it was probably self-installed. Exhaust leak is also on the list, but if you had one of those you'd proabably hear it.