Hey guys, I'm having a problem with my check engine light continuously coming on. Last night I did an OBDII scan, and the result was a P0170 code for fuel trim malfunction. What does this mean? what is fuel trim? and how can I fix this problem? The car is a 94 C220. So if anyone can help me out, i would be very thankful.



take care

__________________
My Cars
Mercedes CLS
Mercedes C-Class W203 - All time favorite

R.I.P.
Mercedes C-Class - W202 Lemon
Mercedes ML - Warrior
VW Jetta – Worst Car I ever owned - Alot of problems

It means your FI system is running either too lean or too rich and the computer can no longer compensate for the problem. You will have to figure out which way it is running and examine the possible problems. On most cars, the Air Mass Meter is at fault, or the fuel pressure regulator. Your C220 uses an Air Mass Meter system, and they are prone to failure. Replace your engine air-intake filter often to extend the life of the part.

I'm not sure how much info the SDS gives in terms of adaptation values for the 1994 models, but if it does, diagnosis is usually pretty easy. Suppose your FI is maxed adaption at 1.32, then odds are you have a bad AMM. Replace the AMM with a known good one, recheck adaptations, and I bet you'll have the culprit. If your system is adapting to .67, then odds are the fuel pressure regulator has gone bad. Do as for 1.32.

Also, a clogged fuel filter can cause FI trim problems. When was it last replaced?

__________________
John Shellenberg
1998 C230 "Black Betty" 240K

http://img31.exs.cx/img31/4050/tophat6.gif

Also, unmetered air downstream from maf.[ vac leak]
Pull vac hose off fuel reg and see if any gas comes out of that port. Should be none.

Check this before change MAF

P0170 code - Should I get this tested?

Hey thanks for the response. I changed my AMM about 18 months ago. So i'm hoping its not the culprit again. I want to look into the fuel pressure regulator, where's this part located? and what will help me notice it?

The fuel filter I will get my mechanic to change, I hope that solves the problem.

__________________
My Cars
Mercedes CLS
Mercedes C-Class W203 - All time favorite

R.I.P.
Mercedes C-Class - W202 Lemon
Mercedes ML - Warrior
VW Jetta – Worst Car I ever owned - Alot of problems

Hey Arthur, where can I find my fuel reg? where's it located and what does it look like? I want to check it as you've stated....

thanks

__________________
My Cars
Mercedes CLS
Mercedes C-Class W203 - All time favorite

R.I.P.
Mercedes C-Class - W202 Lemon
Mercedes ML - Warrior
VW Jetta – Worst Car I ever owned - Alot of problems

It's right on the fuel rail..

looks like this

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=23I0RAMEE23U1A25DU&year=1994&make=MB&model=C-220-001&category=C&part=Fuel+Pressure+Regulator

I'll try to find this. The car's running really rich, the fumes just stink! I think this might be causing it.

Thanks

__________________
My Cars
Mercedes CLS
Mercedes C-Class W203 - All time favorite

R.I.P.
Mercedes C-Class - W202 Lemon
Mercedes ML - Warrior
VW Jetta – Worst Car I ever owned - Alot of problems

is this part under the hood? still can't find it...thanks

__________________
My Cars
Mercedes CLS
Mercedes C-Class W203 - All time favorite

R.I.P.
Mercedes C-Class - W202 Lemon
Mercedes ML - Warrior
VW Jetta – Worst Car I ever owned - Alot of problems

Look on top front of engine. There is a vacuum line from the regulator to the intake manifold. Pull the vacuum line and check for gas. If it is damp the regulator has gone south.

__________________
2012 E350 Bluetech

Hey thanks for the details. I looked at the vacuum hose and i noticed it had alot of wear and small cracking...so i put electrical tape over the effected area and will be ordering a new one shortly. I didn't feel or small any gas, so i think the part's working.

I went to a parts store here called Lordco and bought a cleaner made by CRC called "MAF Sensor Cleaner". I followed the instructions and cleaned my MAF, which is only 18 months old right now. I then removed the negative terminal from my battery to reset the car. So let's see if it worked, and how long before the check engine light resurfaces once again.

__________________
My Cars
Mercedes CLS
Mercedes C-Class W203 - All time favorite

R.I.P.
Mercedes C-Class - W202 Lemon
Mercedes ML - Warrior
VW Jetta – Worst Car I ever owned - Alot of problems

trueog, did your CEL return?

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

Hey, thanks for the response.

Yes my CEL light has resurfaced ..... this is not fun...

do u have any suggestions? thanks

__________________
My Cars
Mercedes CLS
Mercedes C-Class W203 - All time favorite

R.I.P.
Mercedes C-Class - W202 Lemon
Mercedes ML - Warrior
VW Jetta – Worst Car I ever owned - Alot of problems

No suggestions, it's just that I had a similar issue where I got the same code. I reset the code and so far it hasn't come back, but I want to be ready for if/when it does...

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

anybody have any more ideas?

__________________
My Cars
Mercedes CLS
Mercedes C-Class W203 - All time favorite

R.I.P.
Mercedes C-Class - W202 Lemon
Mercedes ML - Warrior
VW Jetta – Worst Car I ever owned - Alot of problems

Same malfuntion code came up on my '95 C220 (car was
idling rough at startup).
After looking for vacuum leaks found that the air duct
between the MAS and throttle body had completely
worn through where its clamped to the throttle body.
Wrapped it in electric tape and now car's running smooth
as ever. Check engine light hasn't come back on.
Will get the air duct replaced this week.