Code 171 issue

Please clarify, is the code P0171? If so, that indicates a lean burn condition -- too much air. Did the mechanic clean the MAF sensor (or swap it with one known to be good) and check for vacuum leaks?

 

1. Please do not post the same issue in multiple forums:
http://priuschat.com/forums/generat...-171-lean-condition-bank-1-a.html#post1378473

2. Your post cited in my #1 above reveals that you had used ethanol. That is a key fact that should have been mentioned in your OP in this forum.

3. It may be necessary to replace the four fuel injectors. Your mechanic may be able to inspect their operation by removing them and having them spray into a glass jar. It is possible that they may have been damaged if the ethanol dissolved residue in the fuel system and clogged the injectors.

4. Clogged injectors would result in a lean fuel/air mixture, resulting in DTC P0171.

 

Run the car for another few thousand miles. Use high octane fuel (91/93). If the problem persists, then think about swapping out parts.

 

Okay, please start from the beginning.

1. Did you burn the entire tank of E85 before putting premium in?
2. How many gallons of premium gas have you burned?
3. Are the throttle body bolt/nuts torqued properly? Was a new gasket used for the replacement?
4. Have you tried a known-good MAF sensor?
5. Is the connection to the PCV good and tight?
6. At what engine speed does the check engine light come on? Idle speed, high speed, or randomly?
7. Have you tried disconnecting the 12V battery negative for 5 minutes recently?

 

This may not be related to OP's problem but Toyota says do not use premium gas due to potential no start problem.

 

The other thing being, the energy density difference between regular and premium is not particularly meaningful. So it probably isn't helpful, but at least it lets the owner think they are doing something towards solving the problem.

The biggest issue here is that parts-changing repairs have been made and may have compounded the problem.

 

Andrei, this looks like one of three things.

Try disconnecting the 12V battery for 5 minutes, just in case there is anything for the engine computer (ECM) that needs to be unlearned. The 12V battery is in the back of the car, on the passenger side, under a trapezoidal-shaped floor board. See post #10 in the following thread: http://priuschat.com/forums/gen-ii-...le-vsc-transmission-problems.html#post1363946. But don't get too excited if it is gone at first. P0171 has two trip detection logic, meaning that the first time you start the car after doing the battery reset, it won't (or should not) code. You have noticed that your car will be fine for a day or two but then have this problem -- this is due to the two trip requirement.

It could be that the ethanol concentration is still high even after two tanks.

That leaves the third possibility, an actual problem with the fuel injection system. This problem could be anywhere between the MAF sensor and the downstream oxygen sensor in the exhaust pipe. Proper diagnosis starts with a scan tool. Here, most scan tools actually work, because everything that needs to be monitored is emissions-related. A shop that focuses on getting cars to pass smog/inspection tests would be ideal. However, focusing on the components that were worked on already, the things to check first are (1) a contaminated MAF sensor (2) a vacuum leak at the throttle body. The vacuum leak could be anywhere from where the MAF sensor connects to the intake, the connection of the intake to the throttle body, the connection of the PCV, and the connection of the throttle body to the intake manifold. That's why I asked about the gasket, which is a piece of material that sits in between the throttle body and the intake manifold, in order to create an air-tight seal between two metal surfaces. I suspect a vacuum leak because the code sets at idle after a cold start.

 

They were not guys from Toyota, they were guys from a car dealer's shop. Different things. And when you said "ethanol" they probably assumed that you meant "E10", which is perfectly fine in any modern car, and not "E85" which is OK only in "flex fuel" cars. If they did know that you meant E85 and they thought it was OK, they are idiots and you should not go back to that dealer.

Two points in addition to the advice others have offered:
- Don't ever put any more E85 or premium gas into the car, it would only make things worse.
- Buy a copy of the Owner's Manual for the car and read it. It's filled with info that every owner needs to know, including not to use E85.

 

P0171 codes on 1NZ engines are almost always caused by a faulty MAF. In fact ive never seen one that hasn't been caused by a faulty MAF. Cleaning it won't fix it, I highly recommend replacing it.

 

Sometimes, when there is a vacuum leak, you can spray carb cleaner around the outside of the throttle body while the engine is running and listen for an audible change in the idle. With a scan tool, you can see a change in the fuel trim if there is a leak. But this is probably something that your mechanic needs to look at, since he may have introduced the problem.

There is no danger in running the car this way. Try it for a few more tanks of gas, and if you still have problems, take it in.