My milly has 37000 miles and I just had the CEL light come on. I have driven it about 100 miles and don't notice any difference in performance or fuel consumption. I have been to Auto Zone twice. The first time I only got a code 0173. I went back today and got two codes 0170 and 0173. I cleared the codes and so far the CEL hasn't come back on in 30 miles. Should I go to a dealer or wait?

Also I am a little overdue on my 30000 maintenance. The dealer wants $500 for the maintenance. Can a good mechanic do this maintenance? It doesn't really require any engine work.

I would appreciate advice from someone who knows. I am not mechanically inclined but I do seem to understand what I read in this forum.[ul]

 

those codes are for fuel trim malfunction, both banks. most common is air leak. there are a bunch of plastic tees in the vacuum line system, and they will crack and leak air. if you are going to keep the car for a while, you should invest in a code reader/scanner. this will enable you to not only read what codes are thrown, but to erase them, too. this is a classic case, you should note what codes were thrown, and when. then, clear them. if they come back, then you know you have a problem. if they dont come back right away, you have bought some time. it is not necessary all the time to immediatly fix the problem. for example, another code(s) you will get will be 0421/31, pre cat efficiency below threshold. this is commonly caused by slow/bad o2 sensor(s). our white car has thrown this code several times. i log when/what, erase, and move on. i know eventually i will have to change the sensors(i already have them), but as long as the ce lite stays off, i am ok. what most owners who do NOT have a code reader would do, is take the car to a shop/dealer, who would then try to get the owner to change the sensors/cat, then clear the codes.
500 bucks is a lot for a 30k maintenance. check your handbook, only filters and some fluids are changed, nothing major. do it yourself. if it has not yet been done, i recommend you flush/change the brake fluid, coolant, and automatic transmission fluid also. i also like to use water wetter, and lubegard.

 

Isn't the code 0170 for a mass air flow sensor? That is what the guy at Auto Zone told me.

 

He would have. Probably tried to sell you one too. Great description and advise from kennin. He knows his Millenia's that is for sure. The P0170 is for the Right side bank fuel trim system malfunction. P0173 is same but for the Left bank. Left being cylinders 2,4, and 6 closest to the radiator and Right being 1,3, and 5 closest to the windshield.

Little more information maybe about what fuel trim is and why it can be bad. It is also called adaptive fuel control. Your engine computer has the capability of adapting to changes in fuel mixture caused by say a clogged air filter, worn spark plugs, and even a small vacuum leak. There are two different fuel trims that can adapt. One is called Short Fuel Trim and is for very temporary changes. The other is called Long Fuel Trim and as name implies is for more permanent changes.
Say for example your engine develops a small vacuum leak. Both Long and Short Fuel Trims are default at 0%. When the vacuum leak occurs, the upstream oxygen sensor stays more towards lean side. The PCM sees this and starts adding more fuel a little at a time until the sensor begins fluctuating evenly. As this is happening the short fuel trim for the affected bank of cyliinder begins rising to 5%, 15%, 25%. When it has reached its maximum of 25% then Long Fuel Trim jumps up to 1% and Short back down to 0%. If PCM is still adding more fuel then Short Fuel Trim starts going back up again.This cycle repeats untill the oxygen sensor is showing a good stoichiometric air/fuel ratio of 14.7 : 1. If this cycle keeps continuing untill Long Fuel Trim is at maximum of 25% and Short Fuel Trim also maximum then PCM sees there is a serious problem and turns on the check engine light. Actully it takes 2 separate and consecutive drive cycles to turn on the light but you get the point. Same thing happens if you have an overly rich condition from say a leaking fuel injector except that the percentages go into the negatives. Problem with those two codes is that they do not tell you if you are too rich or too lean. Only that they are maxed. To get that information, a diagnostic computer that can also gather what is called Freeze Frame Data is needed. When the code is set, it also stores this data which can include a variety of different engine operating conditions that were present when the code was set and stored. RPM, Mass air flow voltage, Vehicle Speed, Coolant temperature to name a few. What you need to be interest in most are the ones labled LongFT1, LongFT2, ShortFT1, and ShortFT2. The percentages of these 4 things and if they are positive or negative will point to a clearer direction about what could be wrong.
One other thing to keep in mind as well. If the code is cleared by the scan tool the Fuel Trims are not. They may have cleared the code but Trim levels are still at that same very high or low reading. You can clear the Trim levels by yourself by simply disconnecting the negative battery cable and stepping on brake pedal for 30 seconds or so. (The brake pedal pushing is to bleed off the residual voltage retained by the PCM in capacitors) This will clear the code too.

 

Thanks for the help Baby Huey and Kennin.

 

After resetting the codes and fuel trim I drove 460 miles before the CEL came back on. I also got 28 mpg on a road trip. Maybe the better mileage is due to my new Yokohama tires.

 

Hey,

I just registered on this forum. I have the same codes coming up on my 99 2.3. Coincidently I have Yokahamas that I just put on it. Great tires.

Is there a way check/fix a leak in the vacuum line without taking it to a mechanic. Any advice would be appreciated. I'll take a look under the hood today.

Cheers

Mikie G

 

this job is labor intensive. a lot of stuff has got to come off, just to access these tees. then, you gotta have the tees in stock. and, the tees dont all look like a T. they are a 3 way divider, but not 90 degree. i bought an assortment, they are only a couple bucks each. the job cost me 564 at the dealer. couple of bucks for the tee, the rest was labor, and i think i paid for part of someone's college tuition. the next time, i do it myself. you might even be able to hear them hissing.