I keep getting a P0170 Code on a Check Engine Light/Engine Electronics ... I looked up the code and it says, "Fuel Trim Malfunction (Bank 1). I don't have the foggiest idea what this means? If you have any clues ... I sure would appreciate your help.

Some background: Car is a 1996 E320 (gasoline 6 cylinder). Mileage is 57,500 miles. All maintenance up to date.

Thanks for your help!

Fuel trim can be caused by vac leaks or fuel pressure regulator.
Pull vac hose off reg and see if it drips/smells gas. If it does , change it.
Also look at all vac hoses ..usual suspects on 104 HFM systems are the white plastic hose going across front of engine , under engine front cover .. they heat fatique and crack..also check the cross hose from MAF for any unmetered air being allowed to enter engine.

Thanks much ... just printed out your recommendations and will do checks as you suggest above.

cpiad

Your interpretation of the fault code must be wrong as it implies you have a V configured engine, ie. bank 1 and bank 2.

Your engine of that year should be a straight 6 engine.

As Arthur Dalton mentioned it should be the 104 engine.

Get somebody who understands better to read the codes and interpret for you.

Regards

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Code P0170 for OB2 is also listed as bank 1 for IL6 engines. Bank 2 would be V engine and the code would be P0173 instead. Same code particulars, but different bank..an IL6 would never have a P0173 code.
They just list it as Bank 1 to cover both IL and V engines.

Ok ... here are checks and actions taken:
- pulled vac hose of the pressure regulator .. slight gas smell ... I am assuming the diaphram may have had it ... so I ordered a new pressure regulator. I assume that all I need is a pair of internal retainer ring pliers to pull the old one out right?
- checked all the vacumm lines I could find ... the lines are all attached and look solid ... no collapses or rubbery feel to them. Engine idles steady as a rock ... so I am going to assume for now that I have no vac leaks.
- On checking the cross-over intake air pipe for leaks/cracks ... I removed the MAF and noticed some fuzzy stuff on the sensor plate ... I cleaned the plate with no-residue electronics component cleaner and dried it with my air compressor ...

I turned the code off ... and after a day ... it came back on. Checked to see it was another P0170 code ... so I decided to get a new MAF along with new pressure regulator. Got both at very decent prices from Autohauz.

I expect the new parts to arrive UPS ground on 9/25 ... so I'll have to wait to install and see what happens. Thank you very much for your advice.

Fuel pressiure regulator can be tested with a fuel pressure test gauge.
However , if gas is evident at vac line , that is a simple verification of ruptured/leaking diaphragm. This fault will make both the pressure at the injectors too high and also allow unmetered gas into the intake through the vac hose. Either will upset the fuel trim , thus the code.

Am I right that all I need is a pair of internal retainer ring pliers to remove the vac regulator? Looks like that's all there is to it.

I have a top-notch vac testing appartus ... pulls vacumm and shows reading ... however, I wouldn't know what is a correct reading from a wrong reading. I suppose I could pull a vac and see if the thing holds it ... I am in the process of obtaining a CD shop manual for the car ... apparently the average consumer can't get a paper manual. Having a manual ought to give me a leg up on the thing. I bought the car new in '96 ... and up until now its been Mr. Reliable ... however, even a car with only 57,600 miles that is 10 years old going on 11 will have issues ...

There was a minor hint of fuel smell coming from the vac line, and that's enough for me to assume the diaphram or an internal seal is shot. There's not much to that pressure regulator. Both parts (MAF and pressure reg) came out to about $300.00. I could have spent that much at a dealership and not gotten much beyond getting the code read ... so, I figure throw a few dollars at it and see if the problem goes away. Thanks for staying with me on this ... really appreciate your help and willingness to share your expertise with a neophyte.

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Yeah....... after you release any fuel rail pressure at the service port.

oh, thanks for that one ... could have been a bit messy.

The easiest way to test the pressure regulator is to take the vacuum line off and turn the key to the "on" position. If fuel drips out, there is your problem. If you smell fuel in the vacuum line, it is most likely leaking.
Dave

I've already detected a faint fuel smell ... so I guessed the diaphram was leaking a bit ... also found crud in the MAF .. cleaned it, but light came back on .. so I've ordered both parts ... will install sometime after Sept 25 when UPS drops parts off at the house ... thanks all for the help ... I'll be back with results after I install the parts ... not much more to do in the meantime ...

after you install your parts[which i believe shoud fix your problems] you will need to get the adaptions reset.this needs good scanner with mb software.

__________________
David S Poole
European Performance
Dallas, TX
4696880422

"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
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Well .... I've got a relatively good OBDII scanner ... that's how I read the codes and how I've been turning them off. I learned by going once to a dealership and being charged $75 ... never again. Many of the OBDII codes are generic. I would imagine, though I am not certain; even the code readers MB dealerships use would probably give them the same code and explanation for my type and scope of issue. You really don't need "MB software," and I'm not sure there is specific software that MB uses .. though they do have some special scanners for some MB-unique systems, e.g., SRS. Any OBDII scanner with erase capability will erase/reset the code memory for the generic codes like P0170. I'm sure I've far exceeded my scope of knowledge here ... so, please don't jump on me for trying -- thanks -

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Erasing a code and resetting adaptation ECU parameters back to MEAN values are two completely different funtions........if adaptations are not reset, the ECU will relearn , but that takes time/drive cycles and the code can reappear until that process is complete.
That is what Tech Poole is referring to...........................