PO170 Fuel Trim Mazda Protege - No Answers from Dealer, Help

mazda
protege
gasoline

#1

My odb2 meter says my 97 Protege has a fuel trim fault; I have had this problem over the years.



Most recently the fault code occurred after an air filter was incorrectly installed allowing unfiltered air to get into the airbox.



The dealer said that the code was cleared and all was in specs after the air filter was correctly installed.



They said that the fuel mix was too rich. The check engine light has continued to come on.



What can I do–I am tiring of mechanics–to self-diagnose this issue? What is the most probable cause?



I have replaced the PCV valve, after which the fault has recurred.



I have an ODB2 scanner, I have access to an All Data cdrom at my local library, I am planning to buy a multimeter. I feel I am forced by circumstances–mechanics do not have an answer for me–to figure this out myself.



What are the most common causes of a po170 fuel trim fault? Obviously, the dealer does not want to–or cannot–say what the leading caused of this fault are.



Help!


#2

What about some black tape over the light?? Must you submit to an emissions test?

But if you insist on supporting the auto-parts industry, try an oxygen sensor or two and a bottle of Techron injector cleaner.


#3

Thanks for the reply. Believe me, I would use the black tape solution and move on–I know people who have done it with no negative consequences–but I am in an emissions test state. Beyond this fact, I am getting a rough idle and a lack of power, sometimes, not every day though.

As for the O2 sensors, both are working. The front one is within specs–it was tested when I got a new catalytic converter–and the rear one is new.

I’ll try the Techron cleaner. Have you had success with this cleaner to eliminate a similar issue? How often do you use it? Thanks.


#4

Many times a problem along these lines is related to something like a vacuum leak and you would be surprised just how common this is.

I’d get a vacuum gauge, connect it to the intake manifold, and see if there’s anything going on with engine vacuum.
(And for what it’s worth, the vast majority of techs don’t use vacuum gauges and that’s a shame because so many questions could be answered in 10 seconds if a gauge was hooked up.)


#5

Dirty injectors are fairly common. More so now with the reformulated gasoline…The Techron injector cleaner, for $6-$8 bucks works pretty good. The ultimate injector cleaner, the one used by dealers, BG 44K, $20-$30. Use either with 1/4 tank of fuel or less to get the best result…Usually, the misfire and stumble are gone in 10 minutes if that’s the problem…Also, check your fuel pressure at the rail. There will be a test port for this purpose.

It’s that front O2 sensor that is telling the ECM how to adjust the fuel mixture…If it’s output becomes erratic, the ECM might throw the fuel trim code…Find out what inputs cause the ECM to throw that code…Also, clean the airflow sensing device. A bad reading here will mislead the computer too…Use the proper cleaner. Check for vacuum leaks and disconnected or split vacuum hoses…


#6

Thanks again for your help. One other thing I forgot. Before the last dealer cleared my codes and sent me on my way, they said that the problem was related to “Long Term Fuel Trim,” as opposed to “Short Term Fuel Trim.” Also, when I clear the code myself, I can usually drive for 4 - 7 days before the light comes on again with the Fuel Trim fault.

Would these details lead you to check certain things more? Please advise. Thanks very mucn.


#7

Thanks again for your help. One other thing I forgot. Before the last dealer cleared my codes and sent me on my way, they said that the problem was related to “Long Term Fuel Trim,” as opposed to “Short Term Fuel Trim.” Also, when I clear the code myself, I can usually drive for 4 - 7 days before the light comes on again with the Fuel Trim fault.

Would these details lead you to check certain things more? Please advise. Thanks very mucn.


#8

Check out this link: http://members.cox.net/sciberpunkt/tech/obd/fueltrim/

It refers to a Millenia, but this code & its causes, with a little variation, are pretty much generic across major manufacturers.

In addition to what is listed there, clean your MAF sensor.

For more than one reason, I have also given up on trusting mechanics and try to do everything I can myself. Go get a repair manual for this car (basic one is $20 at auto parts stores - the major brands are Haynes and Chiltons. I think Chiltons is better. A lot of people buy both). The manual will help, including telling you how to evaluate the possible causes on the list.

Unlike Caddyman, I’m not of the opinion that these things can be ignored. As you know from how the car is running, these codes are almost never ONLY about emissions.

Oh - and as ok said - a vacuum gauge is cheap and so incredibly easy, and worth its weight in gold.


#9

*** What are the most common causes of a po170 fuel trim fault? Obviously, the dealer does not want to–or cannot–say what the leading caused of this fault are. ***

Regretably, P0170 seems to be a kind of nebulous code that seems to mean that the fuel mixture is too lean, or too rich, or whatever else the programmer wants it to mean. Why not P0171 – fuel mixture too lean? Or P0172 – fuel mixture too rich? Probably, you’d have to ask whoever wrote the code. Which, of course, you can’t do.

Background: These OBD codes were dictated by the EPA back in the early 1990s. They apparently presented the car manufacturers with a list of codes and a dictate that if the car-mongers expected to sell 1996 model cars, they would check for whatever codes applied to their engine design and report them. At some level, exactly what a code means on a given vehicle is up to the manufacturer – which is more reasonable than it sounds. Different engines and emissions control systems run a bit differently. The EPA defining voltage levels, failure counts, etc would cause no end of grief.

My guess is that the guy at EPA who drew up the list intended for P0170 to cover emission control systems that could detect a bad mixture, but didn’t really know if it was too lean or too rich. I don’t think any such design currently exists. But maybe it could. And if it does, the DTC code system is ready for it.

Unfortunately, you are getting P0170 and all you really know is that it is something different than P0171 or P0172, it is probably related to the Oxygen levels measured at the O2 sensor. I’d say probably the forward O2 sensor, but that is a guess. And you also know that P0170 on a Mazda Protege may not mean the same thing as P0170 on some other car.

If your OBD scanner allows you to examine the output from individual sensors, you might be able to get some ideas what is going on by examining the outputs from the forward O2 sensor. Other than that, I don’t seem much choice other than to work your way through the engine checking components that might cause a bad fuel-air mixture.


#10

Black Tape…


#11

Beyond this fact, I am getting a rough idle and a lack of power

I don’t think black tape will fix the rough idle & lack of power - unless maybe it would be used to wrap it around a leaky vacuum hose.


#12

My understanding of the P0170 code is that the fuel mix is neither too rich or too lean, its just that the system can’t seem to get it right. Thats usually because one cylinder is running rich or lean so the system can’t “lock on” or stablize.

A whole lot of things can cause this, one of them is not the O2 sensor, which is often the first things replaced that doesn’t fix the problem.

The PVC was a good guess, check the supply air tube for the PVC system. Thats the hose that goes to the valve cover from the air cleaner box that does not have the PCV valve. If it has a separate filter, replace it. Make sure the hose isn’t ruptured or kinked.

Spray carb cleaner all around the intake manifold gasket. If it affects the idle, replace the gasket. Also check the throttle body gasket.

Look for leaks in the exhaust system too, they can cause this code.

Pull your plugs to see if one of them indicates a lean or rich condition, that might help point to the right cylinder.

This is one of the harder codes to track down so I wouldn’t be too hard on the dealer.


#13

Thanks again for your help. One other thing I forgot. Before the last dealer cleared my codes and sent me on my way, they said that the problem was related to “Long Term Fuel Trim,” as opposed to “Short Term Fuel Trim.” Also, when I clear the code myself, I can usually drive for 4 - 7 days before the light comes on again with the Fuel Trim fault.

Would these details lead you to check certain things more? Please advise. Thanks very much.