Celica Forums General Discussion Engine and Performance Need advice with diagnostics code P0171

I have a completely stock 2000 Celica GT. The CEL recently came on with error code P0171, which means the front O2 sensor is indicating a lean mixture. Coincindentaly, this happended about two days after I got it back from the dealership to have a brand new transmission and clutch installed (which feels great now...but that's another story).

I cleaned the MAFS, throttle body, and visually inspected any vacuum hoses I could without taking anything apart (Cleaning the MAFS really smoothed the idle and quickened accelerator response). I reset the ECU, but the CEL came back shortly.

I then took it back to the dealer who did the transmission work, who said that it is running lean, but only at idle, and that the O2 sensors and MAFS are fine. They think it's an "intake leak", which I assume could include vacuum hoses, intake manifold, etc.

Any suggestions would be great before I give it back to the dealer to inspect for a day or more.

They said they would need me to leave it a day to diagnose exactly where the leak might be. They had already spent half the day with my car just to tell me this.

Hey Matt, how muc did you pay to have ur clutch and tranny replaced?

Well, I got them to "throw-in" an oil change, coolant flush, new spark plugs, and a new rear main engine oil seal with the new (not rebuilt) tranny and clutch for $3400. I definitely paid dealer prices, but I wanted someone to complain to when something goes wrong. The tranny has a 1-year, unlimited miles warranty.

Nice...Im getting my shit done as we speak...
im paying 3850 for the 60k mile service, a new tranny and cluth replacement...and brake job...

its good to hear what someone else paid for it...

it drives nice tho?

The tranny and clutch are great...very smooth. You forget how nice it felt new over time. Of course, I apparently had a countershaft bearing failing, so it was a little rougher than it should have been for quite some time before it finally blew apart...leaving me with a lot of missing teeth.

Haggard -

You might want to have them do the rear oil seal if it's not too late. It's a cheap part they have to take off anyway, and it would be 500 bucks later if it fails.

shit, my synchros had issues for a while...and they eventually allowed my tranny to destroy itself...oh well...im glad to hear it drives well tho...it was f'd up when i bought it, so i dunno what a good trany costs...ha ha ha...shit happens...

whats that? i think they may be doing it already...

The seal they used is part# 90311-76001. Honestly, I'm not sure where exactly it sits, but another mechanic friend told me to have them do this.

alright, cool man, thanks for the advice...

I'm hoping someone has some insight on my original post (above) regarding my engine running lean. Any advice would be appreciated.

i have the same problem but it's my O2 senor that got shorted out...

i have a lot of electrical problems in my car.

The dealership says the O2 sensors are OK. The wiring looks OK - no visible shorting.

Long story short

OBD Code P0171 & Monitor Icon C
Celica GTS 2000 94000 miles
Mods: Injen CAI & TRD exhaust

CEL came on a few months ago. My car was running like crap. I noticed I was getting less miles to the tank etc. Took in to the dealer said it was my ECU and injectors according to the TSB. They checked my MAFs and said it was fine. Bought new injectors and ECU car runs much better but damn light came back on Took it back in today they checked it for free and they said my o2 sensor was falling out quick to 0 volts. They blamed my air/fuel ratio gauge saying because it is trying to work its screwing with my o2 sensor. Told me they could not do anything till I remove the gauge and bring it back to check if the o2 sensor is bad!

I think that is bs but I dont know what to do to get ride of the CEL and get the miles I use to get to the tank.

I have done/bought new:

Cleaned MAFs
NEW ECU
NEW Injectors
NEW Spark Plugs

Should I buy a new o2 sensor?
Should I get rid of my air/fuel ratio gauge?
Which o2 sensor should I get front back?

I have the INNOVIA 3100 Digital OBDII Code Reader which tells me two things when I hook it up. P0171(running lean bank 1) and the letter C blinks on the screen which stands for Catalyst Monitor.

Any help suggestions or love would be welcomed! Its been a long day dealing with those jerks at the dealer

This is funny. I install my AEM CAI in my garage and everyone elses CAI or SRI screws their celica's up.

-Get the O2 Sensor
-Get rid of your Air/Fuel gauge, your car is not a race car.
-Get both Front and Back 0@ sensors

To get rid of a CEL, take off negative battery cable for 15mins or so and let the thing reboot.

I need some help i have a 2003 celica gt to make things short my CEL came on about a month ago got code P0171(system running to lean) i already changed the o2 sensors upstream and downstream i changed the MAF sensor. But my CEL is still on. Does anyone know what it could be

This is a common symptom of an air leak after the MAF sensor. I believe the GT sometimes ends up with a leaky manifold but check all the pipes first they are much easier to fix.

The P0171 CEL code says "System is too lean" but actually it finds too much air in the mixture and trims fuel at full rich until it runs out of trim and still thinks system is too lean. Inspect your spark plugs to see if system is too lean ( white and dry) or too rich (black and damp).

The P0171 could be a bad MAF or leaks anywhere between the input through the output manifold or exhaust pipe before Oxygen sensor 1 and 2.

After you change the MAF did you reset the ECU for it to remap the fuel trim?

Remove the battery terminal and try to remap the fuel trim. Drive the car around a few days for the ECU to remap fuel trim.

Hi everyone,

Yes my Celica show the DTC: P0171 System Too Lean (Bank 1).

What i've done so far:

Replaced MAF by Denso DMA-0108
Replaced both heated O2 sensors, by Denso DOX-0273 and DOX-0274
Replaced fuel pump by Denso DFP-0103 and toyota spare part fuel filter and o'rings.
Replaced intake manifold gasket by toyota spare part

The light only turns on, when the car is idle, the car runs normal...

Short fuel trim shows 25%, several ECU resets, no leaks on vacuum line, several tests...


Any suggestion? Or should i give up...


Thank you!

Hello everybody
I don't know how to explain what's going on with my celica
it works just fine the only problem it's when I get gas and start the car it turns right off after 15 sec every time I get gas i have to turn the car and drive it
i have the p0171 code
I don't know what's wrong i just replaced the spark plug

After getting gas I have to drive it right a way( like Within a second) or turns off

P0171 is system too lean bank 1.

After getting gas and restart the car, it turns off after 15 sec?

If you restart again and it runs OK, then it's not the fuel system.

It could be a very dirty or defective Mass Airflow Sensor on top of the air intake hose, right behind the air filter. Swap in a known good air sensor to test if that is the problem. Most Toyota and Lexus use the same MAS from DENSO.


The MAS most times just needs to be cleaned with non-residue contact cleaner. Also it may look good and test good, but could be electrically damaged.

You already replaced lots of parts. Check the wiring around the MAS to make sure they are in good shape.

Could be an air leaks. Check all air hoses around the air filter box. Make sure they are all plugged in and not broken and no leaks.

You may have to do a smoke test to find the leak. Idle engine at night, blow smoke into the air intake. Shine a bright light in the engine bay to find where smoke is leaking.

Good luck.

so....did u ever find out why u were getting the p0171 code? I'm having the same problems and cannot figure out what is throwing the code...

Fuel injectors. I just replaced mine yesterday for the first time after 394k miles. P0171 kept popping up last couple of weeks and engine bogging at 4500 rpm upon hard acceleration. So far no P0171 code.

I had a P0171 with a Lexus, could not find any leak. Cleaned the MAF, same problem. Swapped in a MAF from another Toyota. It solved the problem.

The MAF may be cleaned and tested OK but still malfunctions.

Swap in a known good MAF. Most Toyotas and Lexus use the same DENSO MAF.

The problem could also be a misinstalled or damaged air filter. check it and make sure everything fits and air tight.

thank u for the feedback. im gonna order a new maf right now from toyota. I already bought one, but it was used so it could still be the problem. im also gonna look into cleaning the fuel injectors and if need be replacing them. thanks again. I've already changed the air filter, cleaned the throttle, checked the hoses for leaks, changed the pcv valve, new intake gasket, new spark plugs and new o2. sensors. and that darnn code is still there. its frustrating because my acceleration could be better and it idles rough when I start the car. and I dont know if there's extra air coming from the intake. I hope that im just being paranoid....anybody else have problems with the intake manifold?

Also try new ignition coil set. Use Denso. Bad Coil could be causing rough idle and hesitation. EBay sells a set for about $70

The P0171 code is engine runs lean. Bad ignition wires and coils would pull misfiring codes.

Buy all electronic parts directly from DENSOAUTOPARTS.COM, authentic, lower prices, reliable and last long. There are so many fake DENSO parts sold in eBay it makes me sick. Most auto parts sold in eBay are craps.

Cheap generic ignition coils sold in eBay usually die after 20K miles. Original DENSO coils last over 300K miles. I still have a few original DENSO coils in my car after 320K miles so far..

Bought a BOSCH coil and a AC DELCO coil. They lasted over 30K miles so far.

Possible any of the air hoses from the air box may not be plugged in properly at both ends. Make sure they are all plugged in at the right ports

There could be cracks or leaks on the air intake hose. Run engine, spray soapy water on the hoses and look for bubbles or sucking holes.

Another possible cause of P0171 is clogged or dirty fuel injectors in older cars.

Try a couple bottles of injector cleaner in the fuel tank. Thay may help. Or ask the shops if they can clean out injectors with reasonable costs.

Or DIY spraying GUNK cleaner into the injector's inlet through a hose. Energize the injector valve with a 9-12 V source. Spray cleaner through then blow compressed air through it. Repeat a couple times to clear out any deposit: .



or buy a new set of DENSO fuel injectors $135 with alleged life-time warranty:

https://www.ebay.com/itm/Genuine-NE...004-2005-Toyota-Celica-1-8L/283545341434

I checked DENSOAUTOPARTS.COM. It does not list any fuel injectors. Don't know where an dhow these sellers have new original DENSO injectors.

It may be much later than the last message, but I believe it will help many like me.
For all those who have a problem with the P 0171 on Celica models like me and have tried to change the MAF, replace the O2 sensors and everything else, watch this video to fix the P 171 error

It will save you time and maybe money if you haven't replaced everything before.

People have reported lots of problems with fake DENSO fuel injectors sold in eBay and Amazon.

May be better to clean out your original injectors, or look in ROCKAUTO.COM. There are a few brands that may be reliable and cost 1/5 dealers' prices.