Check engine light P0170 and P0173 - PeachParts Mercedes-Benz Forum

tabo · #1 10-04-2002, 10:24 PM

I have a 98 mercedes benz ml320 elegance, 81,000 km, V6 with a check engine light on... My obd2 scanner shows up DTC's p0170, and P0173, which stands for

P0170 Fuel Trim Malfunction (Bank 1)
P0173 Fuel Trim Malfunction (Bank 2)

has anyone dealt with this problem before? I know its not the O2 sensors.. I don't know where to start.. but from your experience which part should I replace???

Replace Intake Manifold Gasket
ECU Sensor
MAF Sensor
Fuel Pump
EGR Valve

I believe this is a common problems from the ml320's.. I also attached some data maybe it would help you have some idea on the solution! Thanks!

Gilly · #2 10-05-2002, 05:04 AM

In over 90% of these 2 codes, it's the mass air flow sensor. Other 10% it's a vacuum leak, usually in the induction system after the mass air flow sensor. You could also look for a huge blockage in the filter box, we had one once where mice or squirrels attempted to build a nest in the bottom of the air filter box, which realy plugged the airflow. Ran bad too though and had these codes. Pretty confident it's the mass airflow sensor though.

Gilly

tabo · #3 10-05-2002, 09:39 AM

Sensor, Air Flow 112 094 00 48 $532.00 canadian... that one really bytes =( first I'm gonna try cleaning it.. with carb cleaner first.. hope that works! hehe... is it that short piece of pipe intake that has a little sensor stuck to it? its connected to the pipe intake which is connected to the air cleaner assembly?
If this is really the correct part, its funny how the 99 C-class's and 99 E320 and E430 uses the exact same part, I believe MB deliberately makes this sensor break down at 80,000 kms cuz my other friend have the EXACT same problem after warranty =( coincidence?

thanks alot bro...

Gilly · #4 10-05-2002, 08:04 PM

To the best of my knowledge, all of the 112 engines use the part number you quoted, so all the MB V6's use it.
On the modular V8 (113 engine, ie the E430 you mentioned) it actually looks like the same part, but you will notice the part number begins "113" instead of 112, not identical parts.
Yes, it sounds like you are describing the location accurately for a 112. On a 113 it's a little trickier.
We have had many mass airflow sensor problems, mostly on 112 engines. I don't believe the problem is isolated to MB, I believe other manufacturers are having troubles with these as well.
I don't believe trying to clean it will help, may make it worse in fact. But if it's not under warranty, it's yours to play with.....

Gilly

Arthur Dalton · #5 10-05-2002, 10:04 PM

< >>>

Sure are .. I just read an article that some are going back the Hot Wire system [ original MAS sensors type LH-SFI], as they had less problems [ mostly heater burn-off] as they are having with the Hot Film....HFM-SFI system.

tabo · #6 10-06-2002, 05:19 AM

still.. I confirmed the price with MB it is $605 before taxes.. a fter taxes will be a $690... canadian funds.. thats alot of money for a stupid sensor.. other car brands cost like $50 only .. this is outrageous... just for the name!

tabo · #7 10-06-2002, 09:16 PM

I know you probably gone already.. but anyone here know after I install the MAF sensor do i really have to get MB to reset the computer? or can I do it myself by unplugging the battery? I hope they don't charge me much for reseting it =/

Gilly · #8 10-06-2002, 10:13 PM

I kinda pop in and out at will.
To the best of my knowledge the code will need to be erased to make the light go out. Being a dealer guy, I can't say that with 100% certainty, but I believe it's true. What I mean is that we've got the equipment in the shop to do this, so we've never had to look for another way to do it.

Gilly

tabo · #9 10-06-2002, 11:25 PM

either unplugging the battery for 20 secs.. or using a ob2 diagnostic tool (i have the laptop one)! than I can simply swap it and hope it works =P is it safe to drive the car with the mass air flow sensor not working? the car still runs but with the occasional hard shifting.. not very major thou.. do u agree it is still be safe to drive? I'm sure the computer knows the sensor is not working and is running at default flow?? I found out other mass air flow sensors for some other cars are actually pretty expensive in the mid $200-$300 US price.. and I worked on a volkswagen golf and it had a mass air flow sensor as well.. guess its most common on european cars...

btw.. you are right the e430 uses the 113 094 00 48 which is not the same as the m class

Gilly · #10 10-06-2002, 11:45 PM

You have to be careful how you word this. The mass airflow sensor which begins with the 113 number WILL work on an Mclass IF the Mclass is a V8. It is different because of the motor displacement, not the chassis.
The engine will NOT run without a working mass airflow sensor. Your mass airflow sensor is no longer accurate (it works, but it's not an accurate reading). the engine conrol module has compensated for this inaccuracy as far as it is able, and can not adjust it any more, that is why the check engine light is probably on. I can't swear to it without examining it myself, but this is the common scenario.
I've already told you about getting the light to go out in my previous post, I hate to keep repeating myself. I don't believe disconnecting the battery will do any good. I COULD be wrong as I don't need to try this in the shop I work at. Your OBDII scanner I believe should be able to do this though.
If you can monitor your self-adaptation values, at this time you will probably find them maxed out on the high side, Max high is 1.32, max low is -.68 (1.00, + or - .32). Replace the sensor, clear the code, and drive for about 5 to 10 miles. Recheck the self-adaptation (partial load) should be much closer to zero. I don't believe a generic scan tool will allow you to erase the self-adaptation values, but if it does, DO NOT erase the self-adaptation values!!!!

Gilly

tabo · #11 10-07-2002, 03:00 AM

I don't know what is a self adaption value... didn't learn that yet unfortunately.. I guess I'm gonna just trial and error I believe in you.. its probably the MAF..

sdanville · #12 01-08-2007, 09:17 PM

Gilly- I cannot tell you how long it took me to find this post.
quote: In over 90% of these 2 codes, it's the mass air flow sensor. Other 10% it's a vacuum leak, usually in the induction system after the mass air flow sensor. You could also look for a huge blockage in the filter box, we had one once where mice or squirrels attempted to build a nest in the bottom of the air filter box, which realy plugged the airflow. Ran bad too though and had these codes. Pretty confident it's the mass airflow sensor though.

I bought not one but 2 sensors thinking the 1st was a cheap $90 ebay chineese one. replaced the plugs..paid a pro $90 claiming he found a wrongly routed vacuum line..
then reading your post i sprayed starting fluid around the mass of vacuum lines in the back of my engine near the firewall and heard the RPM's pick up.
It took another 50 minutes with mirror and flashlight to find a gizmo came out of its hole to the intake manifold. Just wanted to thank you. Steve.

fema · #13 01-15-2007, 07:24 PM

I may have the same problem and wanted to get an opinion here (my search function for other simlar posts doesn't seem to be working):

In the fall the Check Engine light came on intermittently and finally stayed off until now. Also, a couple of times lately the Fuel Reserve light blinks; this also happened to me once in the fall. As well of late, the car will crank with the key released in the on position, but not start - never heard any car act like this, engine cranking but clearly not going to start and key released.

Coincidentally this week the weather has been super cold, neg 15 last night, and the car does stay outside all year long. There was rough running yesterday morning, and today it would stall when put in gear until a few minutes warm up. Then it ran fine, check engine light still on.

Since I am 3 hours from a dealer, I will take it to the local guy this week to check codes but in the meantime wondering if anyone has a clue - thanks.

sdanville · #14 01-15-2007, 07:28 PM

The only time my ML320 would stall and maybe start up or maybe not start back up..was the cranksthaft position sensor. One bolt to replace.
I paid about $75 online.

Yours sounds like maybe a fuel pressure check is needed.

fema · #15 01-15-2007, 07:40 PM

Is this something that will come up when the mechanic checks the codes? Whiel I've been doing more and more of my own work on the vehicle, I don't have a code reader I hate to start replacing stuff by trial and error.

On the other hand, if it is a maintenance item to replace certain sensors preiodiclly I don't mind going in there and doing this - I have 128K miles and am the original owner. Are there certain "easy" ones to replace like the CPR?