Engine light problem on 2005 Toyota Corolla


Asked by Mar 02, 2015 at 02:42 PM about the 2005 Toyota Corolla LE

Question type: Maintenance & Repair

I', having a problem with my engine light, which first came on over a year ago in Jan. 2014. I  took the car to my mechanic, who I trust and who has been servicing the car since I bought it.. The diagnostic code that came up was P0171. He said that there were a few things that could be causing the light to come on. But he thought the first thing to do was to replace the front air fuel ratio sensor which cost $280 for parts and labor .So I had it replaced.  I should mention that I always put the air cap on tightly, because that can cause the light to come on also. Then, last November, the light came on again and he put some fuel cleaner in the gas tank. It came on again this past Jan. 2015. He then replaced the mass air flow sensor for $191, parts and labor. Now, a month later,  it has come on again. I am so disgusted but I don't know what to do.. The light doesn't blink and it's always the same code that shows up. I know it's not dangerous to have the light on but I know I won't be able to get the car inspected, which is due in July. Any advice anyone? I can't afford to keep putting in new sensors!!  Also, do you think my mechanic is bilking me? Is there any way to get a better, more accurate reading on the problem? The car only has 70,000  miles.

7 Answers

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

2 of 2 people found this helpful.

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?

1 of 1 people found this helpful.

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

1 of 1 people found this helpful.


1 of 1 people found this helpful.

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

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