BOBSBENZ31

I have a 2002 ml320 with 130K. While in drive at a stop it misfires but ok while driving. worse when the motor is cold. occasionally it ill lose power while driving for 1-2 seconds as if i just let off the gas. Im getting multiple misfire codes as well as p0131(low voltage o2 sensor bank 1 sensor 1) as well as p0456 ( evaporation emission system leak detected). My questions are, would a bad o2 sensor cause the low voltage? Also bank 1 sensor 1 is the passenger side front sensor correct? If so that would leave me to believe that is causing it to run too lean and misfiring (p0171 bank 1 lean). I could really use some help before I start replacing parts I dont need to especially since yesterday i dropped $1k in my a/c on my c230. Also got p0302 code which is cyl 2 misfire.

Maj. Dundee

Bob, Bank 1 is on the passenger side, not the driver's side.

Replace the upstream O2 sensor on that side.

The cause of code P0456 could be the sealing of the gas cap. Remove it and inspect the O-ring for cracks. If so replace the gas cap. If the cap is OK then you will have to have a Smoke Test performed by a mechanic on the Evap. System.

You say that you have multiple misfires but only list P0302. Do you mean Random Misfires (P0300)?

Also, code P0171 (which should be P0170. There is no P0171 for M/B) is probably being set because of the bad O2 sensor.

Get these things done and then see if code P0302 still remains. If so then you will have to start switching spark plugs from #2 cyl. to another one, then check for misfire on what cyl. If it still remains, then switch the ign. wire to another cyl. and check for misfires.

BOBSBENZ31

Thank you. I'll switch the o2 sensor n go from there. These codes are from a generic cel code reader and not a star. I really appreciate your help. My wife drives it with our 9 month old so I'm terrified of it breaking down on her. I'll update the results.

Maj. Dundee

Please update your profile by adding the year and model ML.

BOBSBENZ31

Done

BOBSBENZ31

Put the new o2 sensor in. Very easy to do. Fixed my idle problem and so far no power loss.

JERICHO DELANSI

Hi Sir!
Glad you solved your problem..
I bought a 1998 ml230 2 years ago.It runs great until 3 months ago.The problem started with hesitations upon initially stepping on the gas every time you shift gears(manual transmission)but ones you got going,it runs fine.Now even the idling gets rough intermitently and if you step on the gas it backfires then dies on you.The problem intensifies when uphill but turning off the Aircon helps.Ive replaced the airmass,sparkplugs,fuel filter even tried on a new throttle valve with no success.I took it to the mercedes dealer but the dealer said it shows no error codes because the All Activity module(AAM)does not match the trucks actual VIN No. so it doesnt effectively communicate with their diagnosis equipment.They advised me to change the AAM so it may work with their equipment, then they might be able to tell me whats wrong.The AAM is too expensive and as I found out,the AAM is not the control module for the engine. I will appreciate any help or suggestions.Help Please!!thank you in advance.
Regards,
Jericho

Maj. Dundee

As usual, M/B dealers stike again. The AAM, which stands for All Activities Module, is another name for Body Control Module. It controls wipers, lights, signals, horn, locking system, etc. but has nothing whatsoever to do with the running of the vehicle.

Problems going uphill and backfiring is a classic example of a clogged catalytic converter. You don't say what misfire codes you have but if they are cyl. 1,2,3 then it is the pass side; 4,5,6 is the driver's side.

JERICHO DELANSI

I appreciate the prompt reply Major.I knew it!!the AAm doesnt have anything to do about the problem.As for the catalytic converter,I have tried running the engine without a catalytic converter by drilling a whole on the exhaust pipe just before the catalytic conv to see if it makes a diffrence.. but the problem persisted.
The hesitations and backfiring does not only happen when uphills..it happens on every initial accelerations after shifting gears.I have to find out what misfire codes i have..Ill let you know soon.But what could be causing it??Thank you so much..

Maj. Dundee

Why in the world did you drill a hole in the exhaust pipe? The correct thing that should have been done is remove the upstream O2 sensor on the suspected side and take a test drive.

If you don't remember the misfire codes, how did you know what side to drill a hole in? As a matter of fact, what side did you drill a hole on?

JERICHO DELANSI

Hi Major!ive tried cleaning the O2 sensor with an electrical spray cleaner but it did not help.I do not have misfire codes because there are no fault codes appearing on the MB dealers diagnosis machines.
Ive been doing some research and it seem the symptoms are either from ECM or camshaft position sensor.My truck is only a 4 cylinder engine(ml230) manual transmission.Your ideas will be much appreciated.Thank you.

Bmadfamily

Similiar issue. While coming out of the store my ML500 started up like a loud truck with rough idle. Plugged it up and got CEL codes P0131 and P0456. I can also smell exhaust fumes, gets louder during exceleration. We changed the O2 sensor to a bosch on "passenger side" code P0456 code went away but still getting P0131, loud/rough idle and exhaust fumes?? Can this be a leak in the exhaust? Cat converter need to be changed? Vacuum Leak? Or fuel filter? This is a major headache! HELP!

Maj. Dundee

If your truck is right hand drive, you changed the wrong sensor.

In any event, PLEASE UPDATE YOUR PROFILE in USER CP to include where you live.

Code P0456 is for a small leak in the Evaporative System and has nothing to do with changing an O2 Sensor and clearing code P0456.