Hi guys,

I had the code P0173 and changed the MAF.

After that I got:
(+)The code gone.
(-) the start of the engine is not smooth as before (if I wait 5 sec with key on before starting is better)
(-) The gear change 2nd and 3rd is not smooth as before.
(+) Better gas mileage (according to computer)

There was before also a rough idle and now is little improve but still some.
Question: Is the maf not good?
It's from ebay and has no bosch/mercedes sign on it, but the bosch serial number.

After one week I have check again with the reader and got P0170 and P0173.
Could be O2 sensors or leaks?
Thanks,

The car is S320 (w220) from 2000 with 95k miles on it.

 

P0173 is a Fuel Trim Malfunction on Bank 1
P0170 is a Fuel Trim Malfunction on Bank 2
I believe you must have a defective replacement MAF.
I only use Bosch sensors although Pierburg should be OK.

Do you have the correct sensor. Different engines have different sensors and likewise there is a difference between Petrol and Diesel.
S320 (M112) sensor should carry the number F 00C 2G2 025 and 962 12 2B on the small sensor electronics box. This is not the Bosch or MB assembly number.
Bosch sensors are marked with Bosch on the sensor electronics box (not the big housing that fits it into the air intake system)

Was this a new sensor or one that looked like new?
Was it from an etailer (shop) or an individual?
Maybe the guy has sold you his old defective one?

Real way to tell what is going on is to get LTFT Long Term Fuel Trim reading (using an appropriate scanner) from the OBD. If this is >30 then the ECU will report a Fuel Trim problem. Basically the ECU can't get the mixture correct to give the appropriate emmissions (O2) reading.
Did you reset the code? If not the LTFT takes some time 2 or 3 restarts (trips) to come back within limit since it is an average value of the instantaneous STFT (Short Term Fuel Trim) values which should run +/- 10
Could be your O2 sensor is defective but these are expensive and it is better to check their function (response characteristics) in real time with an appropriate OBD scanner.

Hope this helps,
Stuart

 

@snanceki
Thanks for quick reply.
The MAF looks new.It is the correct bosch part number but no bosch trade markt.
It was from a german garage which sell as individual on ebay.
I have ask the seller what is the suplier of this maf but no reply.
I will wait to buy carsoft multiplex for deep check.
Would you recomend a Bosch suplier delivering in Europe?

 

Hi,
You don't need Carsoft to read the additional data. Carsoft is good but expensive.
My Dyno Scan 150 USD scanner works just fine. There are hundreds of other scanners available that can read this sort of data for >200 USD but you need a PC (windows) or Palm PDA in the case of Dyno Scan to use the software. Basically you just need to connect to the ECU via the OBDII connector to read live data being fed to the EMS ECU.
Maybe your MAF is O. However something is obviously wrong. No reason why the MAF should be faultry subject to the sellers reputation.
The sensor should have "Bosch" and "Made in Germany" on it.
What is the number AND LOCATION of the number you state as being correct.
Did you just get the sensor or the air inlet housing with it? Bosch and Mercedes onlt sell this part as an assembly!
The part number on the air inlet housing is dubious since it refers to the assembly. The part number on the sensor "electronics box" anout 15mm square is the number that is important and refers to the sensor. Somebody could have "assembled" the wrong sensor into the correct housing!
I repeat that there are several different types of sensor dependent upon fuel and airflow.
Regards,
Stuart

 

Well I have found the multiplex the most extensive tool and with only $160 +$50 for shipment.
www.uiftech.en.alibaba.com
The Bosch serial number is 0280217515 and is on the housing.
I didn't take out the sensor from housing due to missingthe tool.
Meanwhile I have ask another seller on ebay about Maf origin and the response was negative no Bosch origin.

 

I'm confused. I'm trying to help you.
So you have a good code reader. So what are the LTFT and STFT values?
Likewise what is the O2 reading and is it cycling correctly?
If you don't have these it appears that your "extensive" hand held "multiplexer" is only able to read codes.
As I stated the number on the housing body isn't definitive because it is the sensor that is important and this can be dismantled from the body.
Sensors other than Bosch will work if they have the correct characteristics.
So what make of sensor is it and what is its correct application.
P0170/P0173 nearly always points to an out of range MAF but it is just possible that some other component could be causing the MAF offset circuit to require a value outside of range.
i.e. LTFT >30
Stuart

 

Sorry,
Curently I have only the simple engine/transmision code reader.
I want to buy the multiplex, I don't own one yet and I don't know someboby with live data reader.
I hope I will get those LTFT and STFT value soon.
Meanwhile I have also found a seller with Bosch MAF 3x the price of what I took
So in case I will need new one I know were to go.
Thanks for help.

 

So after I have receive the Carsoft I notice that the values LTFT and STFT cannot be display only thing I got in % was some Lambda before catalytic left and right (could be this STFT?!).The value changes quick from - 2<10 to + 10.
Anyway I bought a new Original mercedes MAF and installed.
After that I got just after engine start some missfires on cylinder 1&2 and O2 sensors errors: P0150 and P0130.
Before to start I have reset adaptation.
After another week I got again P0130.
After 2 weeks just missfire on cylinder 4.
No more P0170&P0173.
Could be that after MAF change the O2 sensors need also changed?
The fuel ratio look good, the start is smooth and the idle is very litlle shaking.

 

Hi,
The STFT changes quickly around 0 if the fuel metering / monitoring system is working correctly.
The LTFT shows the "offset" applied at startup to position / centre STFT around 0.
Once the LTFT offset nears 30 (units are %) the OBD reports an error stating that the Fuel Trim circuit is out of range. This usually requires a new MAF sensor.

I still believe your problem is the MAF sensor. However if you can be sure that the MAF is the correct one and not defective then it must be something else.
The number on the MAF housing does not identify the sensor, only the housing!! Petrol and Diesel engines have different sensors.

Did you check for O2 sensor cycling.

The key to all of this is having a good scanner. Your M112 (2000) engine OBD supports STFT and LTFT live data and likewise 02 sensor (single sensor per bank) data stream.
If you PM me your email address I will send photos of my DynoScan (Auterra) Palm display.

You say the car has done 95k Kilometres? (mine is now at 120k Miles) what is the SERVICE HISTORY. When were plugs, air filter, fuel pump filter etc last changed?

How else can I help.

Stuart.

 

Thanks again Stuart,
The plugs have been changed at 60k (36k ago) air filter at the last service (B service 6k ago) the service history looks ok, every 10-12k was there an A or B service done.
For fuel filter I cannot tell.
Monday I plan a visit to dealer so any advise would save some diagnostic time and money.
I will ask them to chek the plugs and changed if they are burn.
I also have another symptom: on freeway there is power loss on medium to hard acceleration.