Engine light problem on 2005 Toyota Corolla

P0171 is lean condition. Maybe unmetered air getting in to intake, from a vacuum leak, a faulty MAF, and possibly a weak fuel pump not supplying enough fuel. If he can't diagnose it, which is even harder for me from behind a keyboard, (at the risk of flattering myself I know Corollas and the 1.8 1ZZ FE better than I know any other car. I have one) you need to take it to a Dealer. Have it fixed properly once and for all. Have a look here also: http://www.samarins.com/diagnose/p0171.html

By the way, there is no such thing as a "front Air Fuel Ratio sensor" the fuel trim is determined by the ECU using signals from the MAF.-- MAP.-- o2 sensors-- all in concert. A vacuum leak from a large source such as PCV throws everything off. Even a bad camshaft position sensor can enter the picture, but this is unlikely. But that would effect the timing and amount of injectors. Your car has coil on plug ignition, and timing is crucial. I am fully aware of cost of dealer service but they have diagnostic computers most shops can only dream of owning

Thanks very much. I hesitated going to the dealer because they can be so costly but I guess I have no choice. I hope I don't get a runaround from them too. Maybe they have a better code machine?

Much better. That's what I meant by they have diagnostic computers most shops can only dream of owning. Toyota -specific diagnostic computers that run upwards of $15,000. A do-all shop, even competent, honest mechanics can't afford Toyota-specific ones.

One more thing if I may: Important to buy Brand-name gas. Gas at convenience stores and independent retailers even Pilot, Loves's, are made by small refineries that do not have detergents and other additives that (not limited to but include) Shell, Chevron, Exxon/Mobil, 76, those big names. Cheap gas is, well, cheap gas

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Time to take your vehicle to an ASE certified technician that won't start firing parts at the car immediately after gathering the vehicle's DTC's. Find a technician not a mechanic. As an automotive service professional, the word "mechanic" makes me cringe. I'm an educated, well versed "technician". To me a "mechanic" repairs mechanical components. A technician is an educated professional who understands and executes the 6 step diagnostic and repair procedure. Nowhere in that procedure does it ever recommend replacing a random part in hopes the vehicle becomes fixed. Backyard mechanics are the ones who follow the "Well, lets just replace some parts and hope it starts" mantra. Diagnosis is what separates the men from the boys. Anybody can learn how to change an old part with a new part. That's caveman stuff. Knowing a system's functional operation is half of the battle. If you do not study or research function & operation of a vehicle's system prior to attempting diagnosis, you'll always be guessing. How can you understand what's actually wrong if you aren't 100% sure how that system works? I spend most of my day reading and comprehending service information after verifying the customer's concern. If I cannot duplicate the concern and there are no DTC's, why continue chasing a ghost? If I do verify, depending on the concern, I'll most likely plug in the OEM scan tool and print any and all DTC's. At that point the research begins if I'm not 100% familiar with the certain vehicle or system. Your mechanic is what we call a "hack" or shade tree, hillbilly mechanic. Probably uses lots of zip ties and either duct tape or electrical tape. Most likely doesn't own or know ow to use a Digital Multi Meter

My 2005 Corolla has the "check engine" symbol on again! It's been coming on and off for the past 14,000 miles. I've had 3 different mechanics, including the dealer, do a diagnostic which mentions the transmission. However, it's a little vague as to what part of the transmission. And in 14,000 I haven't felt anything wrong with the car! I had accidentally run up over a curb onto a little island, and then had to drive off of it. It was on the way home from that incident that it first happened. I had good mechanics look under the car when it was on a lift and they checked over the car and found nothing. It was off for a while now, and after a long 70 mile trip, came on again. I don't feel safe going far in the car and I'm afraid to buy another new Toyota and get the same problem.

GuruZQS12 CORRECTION!!!!! I have a 2006 Toyota Corolla, NOT a 2005 as I stated above. And, lo and behold, the CHECK ENGINE LIGHT went off again after about a week and I did NOTHING for that to have happened. Who can figure?

I have a 2005 Corolla and long, long story short, I firmly believe the "Check Engine Light" and code system is faulty! Light has been on and off for about 4 years now. When it comes time for a smog check, I have to catch it during one of the OFF periods. Have learned that if the "Light" is the only symptom, ignore the light.

I a 82 and living on social security. I can't afford a new car if something is major, and I love my 2005 corolla. I am paranoid about my car breaking down on me be on repair. What do you think?

Same as 528MQ, I also firmly believe the Check Engine Light System is faulty. First time mine came on dealer told me "code" indicated I needed transmission work to the tune of $3800. As the light was the ONLY symptom of any problem, I declined. 5 years later I've still not needed to do any transmission work. Now I just ignore it and catch it in one of it's OFF times when I need to smog.

My 2006 Corolla's "Check Engine Light" is still going on and off for about 30,000 miles without feeling anything wrong with my car. It usually comes on after a long trip, but on the way home. Lately, it seems to go off after a shorter amount of time, such as the next day. I've been to Toyota, and they wanted $3,500. to fix some type of transmission problem. I've had 2 other diagnostics that say the same thing, but I feel nothing wrong with the transmission. One of the mechanic's diagnostic said that something got stuck, and that mechanic seemed to think it was nothing to worry about. I don't feel safe in my car if I go a long distance since I always wonder if this is the time my car will break down. I still don't feel anything wrong. When I need to inspect the car, I wait until the light goes off again.

I have the same concerns about my 2005 corolla, since I bougth that in 2010 the light come on and off, but since the Toyota changed my airbag passenger the light not go way. I bougth a new car but I need to fix this problem for do the the car inspected, which is due last January. I don't know what to do, some suggest?

If you unplug your battery cable and reinstall it on your 2005 Toyota, the check light will go off for a good month or two. At least you can get through inspection. But maybe not due to I have noticed when I reset the check switch it has a fuel smell like maybe carbon monoxide leak. I believe there maybe be a fuel sensor or a bad catalytic converter. But not sure. Toyota factory rep should be able to diagnose this problem.

I don't believe in those code info from parts houses like Auto Zone, Standard Parts. or Orielly You might waste a lot of money and still have problems. I went to three different auto parts places and got 3 different answers on my problem with the check engine light coming on. If a factory rep trouble shoots your car he should catch that problem .

I did the diagnostics on my daughters 2005 Corolla and it had multiple codes showing, looked up the toyota service bulletin from Jan 30 2006 and the five codes matched with an issue with the charcoal evap unit under the rear axle area. PO43E, PO43F, P2401, P2402, P2419. Ordered parts and cleared the codes but until its replaced the ck engine light will come back on.....