Dexter105

I own a 1998 E320 with 58K miles. Recently I have been
plagued with a check engine light problem. I had it looked at by a shop close to my house(not the dealer) They tell me the codes are P0170 and P0173 Left and Right fuel trim bank(s). They have reset it twice telling me I may have caused this by over topping off at the fuel pump. I dont do that but I agreed not to do it. The light stays off for 8 to 10 hours then comes back on. The cars drives fine...Any ideas?

haspelbein

By just looking at the fuel trim codes, you can't really tell all that much. Fuel trim errors mean that your car is running too rich or too lean. This can be caused by a number of things, among them:

Intake air leaks
Incorrect Fuel Pressure
Injector valve defective or coked
Engine Temperature Sensor defective
EGR valve defective
Secondary air leak
Fuel evaporation control system defective or leaking.
Air Mass Meter defective
Vacuum leaks
Oxygen sensor aging (slow response)
Clogged or damaged catalytic converter
Contaminated fuel
Fuel tank ran empty
Combustion altered by a mechanical failure (Spark plugs, compression, intake/exhaust valves, ...etc.)

I would strongly suggest running a full ODBII diagnostic, and not just reading the error codes. There are a number of parameters that allow the mechanic to get a better idea. My advice: Bring it to another shop or the dealer.

Dexter105

Thanks for the advice....I will get a full diagnostic check. I will check another shop before I go to the dealer. They are fairly expensive for any little thing. I actually talked to them today and told the tech over the phone what I had and the codes and he suggested I come in and get O2 sensors replaced.

haspelbein

Did you ever have them replaced before ? If not, it's probably not a bad idea at nearly 60K miles, anyhow. They're the most likely cause, but you will not know until you either install them or run a full diagnostic. Anythow, they should improve the engine's efficiency.

If you had them replaced already, I'd ask for the diagnostics first ,if I was in your shoes.

Good Luck !

Dexter105

They have not been replaced. Everybody I talk to says the O2 sensors are most likely the cause. Thanks for the help. I am going to get the full diagnostic first and have them replaced if necessary.

Dexter105

Well, I have had my car at 2 different shops. The 1st shop was full of it...all they did was reset the light after keeping my car 2 days and tell me not to overfill my tank...again. The next shop has had the car for 2 days and after doing full diagnostics(thanks haspelbein) has determined the problem is with the Mass Airflow Sensor and is going to replace it. I should get my car back tomorrow...I hope this is it.

haspelbein

Glad you finally found a shop that would do a full diagnostic. Simply resetting the code and telling you to "not overfill your tank" is something I could have done with a $40 OBDII scanner I ordered online.
The first shop either didn't have the right equipment or didn't want your business. You have to spend AT LEAST around $600 (plus a PC to run it on) to run those diagnostics. If you ever have that amount of money laying around, it's actually a very entertaining application.

The MAF may indeed be the culprit. If the shop did a thorough job, you should be just fine.

Dexter105

I have my car back now with the new mass airflow sensor installed.....so far, so good. I have notice a much smoother drive and idle since the replacement.