[43sqd]

These codes are generic codes and not specific to M/B. M/B lumps all Fuel Trim problems (both lean and rich) into codes P0170 and P0173. They leave the determination to the scanner to point them in the right direction.

In your model year it can be narrowed down considerably. Look at the explanation of the different codes. The generic odes refer to running rich which could mean a number of things relating to fuel pressure, O2 sensor readings, restricted air flow (air filter), etc. All these and many more have to be looked at, including the MAF sensor. Don't just go out and buy anything until the correct diagnosis has been made.

Are you using one of those $50 pocket code readers?

 

[43sqd]

Hi 43sqd. I have a proffesional scanner that also shows and monitors engine data should i monitor any specific data from the engine while its idling? Im taking it one step at a time by ruling out the oxygen sensors bc the codes are for both banks and its highly unlikely for both sensors to go out at the same time, ill take a look today at the air filter see if its really dirty but either way i will replace it monday.So this kind of leads me toward the maf since it will impact both banks, the fuel filter i replaced last year at this time with a genuine mercedes oem one so i might rule that out too.Now i drive with the a/c on almost all the time and the engine temp before use to stay in the high 90s-95 which its always been like that and its normal at this time of the year, lately its been staying in the mid 80s-90s im thinking maybe a stuck open thermostat or faulty coolant temp sensor sending wrong signals to the ecu might caause this codes too? I really appreciate your help pls let me know if i need to monitor any special data with the scanner from the engine?

First read the article to give you a little insight into running rich.

Then determine through the use of the freeze frame data when you are setting the codes.

Below is live data on a 2002 ML 320 taken at idle with a fully warmed engine. There were no problems with the engine at the time of the data. Compare yours to the list.

Note: Idle Fuel Trim=STFT and Part Load Fuel Trim=LTFT

Being that you have a professional grade scanner, after you correct the problem/s and all the readiness monitors have passed, make a list similar to this one so you can compare things in the future.

 

[43sqd]

1. There is nothing wrong with the idle speed; it is well within the range.

2. There is nothing wrong with the O2 sensor readings.

3. There is nothing wrong with the MAF readings. It is 3 kg/h over the sample data. Slightly bigger engine, different readings.

4. You are too concerned about other things and you failed to see that the Secondary Air Injection says ERROR. With a cold engine, remove the top engine cover, start the engine and see that the AIR Pump runs and then turns off within 40 secs.

5. Do not clear the codes any longer. When you clear the codes all the readiness monitors are erased and all of them have to get ready all over again.

On your scanner, which is not a professional one, see if there is a selection for checking the status of the Readiness Monitors. The hardest ones to reset are the Catalyst and the EVAP. If the evap is still not ready you cannot have less than 1/4 full tank and no more than 3/4 tank.

If some monitors are not ready you must drive the veh. at varying speeds, but not over 55PMH to properly set them. Nothing can be done until they are set.

Most importantly, the pending code means that the ECM has detected a problem once, after you cleared the codes, during a drive cycle and has noted that. If it occurs again within the next 40 drive cycles it will illuminate the CEL. So after every day of driving, you must check to see if all the monitors are ready.

Wait for the CEL to come on and then check the freeze frame data and post the results.

 

[43sqd]

Okay i checked the air pump it works, You so right for the maf i completely forgot that this is a 3.7 Well i took a short drive to the gas station to fill it up with gas came back put the scanner on no codes i checked the monitors here are the results incomplete. Checked the fuel trim mixture same results -0.7 and 1.5 sometimes 2.3 same as the results of the one you told me to compare it.Im gonna take a drive a little later to brooklyn since you are from bronx and you know NY well i hope it will be enough for the systems to be ready and then ill scan it again thank you very much for your help ill post the results a little later and see what the problem can be.

What did you mean by "fill it up"?

 

[43sqd]

I filled the tank to the half like you said no more than 3/4 and no less than 1/4 i had around 1/4 so i filled with gas to half tank

Thank God.

Don't try and force the monitors to set. Long sustained drives will not do it. Normal city driving will eventually do the trick. Don't get anal about this as they will eventually set.

 

[43sqd]

Well 43sqd all monitors got set and they say ok no codes so far the car drives fine i guess ill wait and see if the codes come up again.

Good show. Remember if a code pops up it did so for a reason. Never clear anything until the problem has been corrected.

 

[43sqd]

Well i really hope it was just a show, iv driven so far no codes, but im having an idea maybe the thermostat got stuck open and now it decided to work again because if it was a bad sensor it would throw codes very soon again they dont get fixed by themselves like the thermostats, should i just replace the thermostat it just costs 25$ an OEM one from autohaus what would you suggest ? Iv bought this truck 4 years ago with 67K miles now it has 105K its been Super reliable the only problems its given have been a broken window regulator, the driveshaft bearing and a transmission cooling line leaking which im gonna replace soon, and just the regular maintenance it has never had an engine related problem.I really appreciate your help you are very kind and very valueable to this forum.

I think you making to much of the temp. Why don't you carry the scanner with you and when you think there is a problem, hook up the scanner and read the temp. directly off the scanner. Remember the thermostat will no open unless it is approx 220F.

If it makes you feel good, then change the thermostat.

 

[43sqd]

Well 10 days later the car stalled while it was idling it turn right on and then 2 days later it wouldnt start i waited like 30 min and it started again it through the CPS code P335 i replaced thr CPS sensor but i just wanted to ask you 43sqd Could it have been the CPS sensor causing these 2 codes too??

Possibly to some degree. Now make sure all the codes are erased.