Error P0170 Fuel Trim Malfunction, (Bank 1) believe it's a MAF (Mass Airflow Sensor) - Mercedes-Benz Forum
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#1 (permalink) Old 11-17-2008, 01:18 PM
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Cool Error P0170 Fuel Trim Malfunction, (Bank 1) believe it's a MAF (Mass Airflow Sensor)

Background

Hello fellow Mercedes enthusiastss. Quick background of myself I bought my first 1998 slk 230 in July. I love it and joined this site which has been extremely helpful
on pointing me in the right direction and avoiding those expensive dealerships. The following is my situation and my thoughts. A lot of the info I have taken from other
posts on the site and compiled it together. If some of you could confirm my thoughts or point me in a different direction it would be greatly appreciated. Wanted a little
feedback before I purchase the part and make the fix.


Symptoms and Error Codes

First my check engine light came on but car was running yet. I didn't notice any performance issues however that could also be from being a new owner. However one cold morning
the car would not start. It just kept turning over but not taking off. Like it was being denied fuel.

I pulled the codes P0170 Fuel Trim Malfunction, (Bank 1) which many posts point to the dreaded MAF (Mass Airflow Sensor) sensor failure.
Also code PO410 Secondary Air Injection System came up which I did not find any posts for.

What I have researched is that problems with Mass Air Flow sensors are common.
Bad or contaminated Mass Air Flow sensor can possibly cause a wide range of various vehicle drivability problems such as
- stalling, especially when the engine is cold,
- misfiring,
- poor acceleration, etc


Function of MAF Sensor

A MAF uses a measured temperature difference between two heated wires in the intake system to judge the speed of the incoming air.
(more airflow cools the wires more and signals the need for for fuel). In the Case of a bad MAF (which I think I have) it signals that less air is flowing past the wires
(perhaps they cool more slowly when they develop a film on them) then the volume of fuel injected for each combustion event will be less. So in general it is used to control
the rate of fuel flow at the injectors needed to burn at the correct fuel-air ratio with the mass of the air being passed through the MAF.


Conclusion

With error codes P0170 Fuel Trim (Bank 1) and PO410 Secondary Air Injection System coupled with it being a cold morning I believe the MAF (Mass Airflow Sensor) sensor failure
is at fault. P0170 Fuel Trim meaning that the MAF is telling the ECU to enrichen the engine and it's reached it's limit.
What happens at that point is other stuff starts acting weird too. I think that is why the PO410 Secodnary Air Injection System code was thrown.



Solutions - Clean or Replace

Sometimes cleaning the MAF may provide a temporary solution to the issue. However this is probably a better solution when noticing performance issues and a temporary solution for that.
If the MAF gets dirty a Can of CRC Mass Airflow sensor cleaner may do the trick.
- Remove the MAF, removed the sensor insert from the MAF (requires security torx) and spray the entire thing and the gold colored wire near the end until it is shiny new.

Recommended cleaners from posts to this site.
- CRC QD Electronic Cleaner
- CRC MAF cleaner

In my case since the car will not start I believe the best route is to replace the MAF. As we all know this is not a cheap part and it is highly recommended going with Bosch.
People have had issues when trying to go the cheap route here with another brand. What I found is in my case with 1998 SLK 203 I have the following engine.
- SLK230 Chassis 170.447 Liters 2.3 Cyl L4 Fuel Gas Eng. Num 111.973

All SLK320's and '98 and '99 SLK 230's have the Bosch removable insert. BOSCH Air Mass Meter B3130-70629 F 00C 2G2 025
The following site Auto Parts at AutohausAZ - OEM Auto Parts - Discount Replacement Parts, Resources and Car Care Tips is recommended on posts from this site and has a very good price on a Bosch MAF for $178 which it returned as a part for my make and model of car.
- Link
Your Parts Search Returned 1 Part(s)


Installation

I have not found any detailed docs on how to replace. So I would imagine it is not to bad of job. The MAF is always located in the intake stream between the manifold and the air filter.
What I have seen is to disconnect the battery while installing. Make sure it remains disconnected for 30 minutes. This will reset all of the computers.
It is also important to ensure there is no air leak, the seal has to be perfect, or else you will have problem. If someone could point me to some more detailed instructions or give me some
pointers that would be great.


Conclusion

Thanks for reading through my post and giving any feedback on my situation even if it is just to say I'm on the right track. I'm hoping when I'm done solving this problem it will be
a good post for future people to look at on how to solve this issue. I will also record my steps on how I resolved the issue when I get to that point.
In conclusion as I become more knowledgeable about my car I can help others like those of you who replied to my post.

Cheers!!!

Corey
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#2 (permalink) Old 11-17-2008, 01:36 PM
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Corey,

I applaud what you are doing. I'm going through a similar drill myself with the PO170 code. Will try the cleaning route first, but need to order the 5-point torx bit first. Benzworld is fantastic, with amazing, helpful info. I have searched the posts and found much useful info, but I think a current summary will be helpful to many in the future. Thanks.

--Larry C.
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#3 (permalink) Old 11-17-2008, 03:05 PM
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To be honest... it might be something other than the MAF sensor. I think with the MAF sensor you get 3 code errors.

Usually the P0170 (MAF sensor USUALLY) goes along with code P0136/P0303/P0243/P0300/P0304

See if any of those codes come up. If so, you might need to purchase a NEW maf sensor as opposed to cleaning it. The MAF sensor can only be cleaned 1 or 2 times before needed to be replaced (usually).

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#4 (permalink) Old 11-17-2008, 04:02 PM
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gakz,

Thanks for the info. I did also get error codes PO301, PO302, and PO303 - misfire detected in cylinders 1, 2, 3. Also PO300 - random/multiple cylinder misfire detected.
Thought this was a separate problem related to spark plugs. I've never cleaned the MAF sensor, and thought that might cure the PO170 problem. Sounds like I may need to spring for a new sensor.

--Larry C.
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#5 (permalink) Old 11-17-2008, 09:06 PM
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Quote:
Originally Posted by Shecko View Post
Also code PO410 Secondary Air Injection System came up which I did not find any posts for.
Try searching for P0410, not PO410. It's a zero after the "P", not a capital "O".

Blame everyone.
Admit nothing.
Be bitter.
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#6 (permalink) Old 11-17-2008, 09:30 PM
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Since you said you did also receive those codes, get the MAF sensor. It should be less than 200$, DO NOT GET AN EBAY ONE.

That SHOULD solve all of the problems... possibly even the 0410 code, itd be worth it to get the MAF changed out ASAP though to find out.

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#7 (permalink) Old 11-17-2008, 10:32 PM
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Quote:
Originally Posted by Shecko View Post
Background

What I have seen is to disconnect the battery while installing. Make sure it remains disconnected for 30 minutes. This will reset all of the computers.
No need to disconnect the battery. It will NOT reset the ME (engine) computer if you disconnect the battery. All engine codes and adaptations are kept in non-volatile memory. The only thing you will reset is your BAS/ESP setup which you will have to resynch afterwards. The SLK is VERY sensitive to disconnecting/connecting the battery and the chances are good you'll end up with a fried instrument panel - search the stickies for descriptions of it.

The best bet is to just buy a cheap scanner to Harborfreigt and reset your codes after swapping the MAF. Alternatively, just start the car afterwards, let it idle for 10 - 15 minutes, then take it out on a GENTLE drive, no hard acceleration or high revving to give the computer a chance to re-adapt to the new MAF. A 10 to 20 mile drive will do the trick.



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#8 (permalink) Old 11-18-2008, 12:46 PM
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Cool

Restating Issue

P0170 Fuel Trim Malfunction (Bank 1), P0410 Secondary Air Injection System, Car will not start just turns over, seems like it is not getting fuel.

Hey Gang,

I checked into the P0410 code more and found the following info from posts on this site.

P0410 Secondary Air Injection System - Look at the cold start air injection system

A check valve under the Air Filter Box allows air to flow into your exhaust, failure of this valve can cause MAF & O2 Sensor problems (Codes I’m getting P0170 and P0410). I have also included a pic of where I believe this valve is located – CheckValve.jpg

- On US models this is used to heat up the O2 sensors and catalyst quickly after a cold start..... the supercharger delivers the air needed....normally-aspirated MB's have an air pump
- A check valve under the Air Filter Box allows air to flow into your exhaust.......failure of this valve can cause MAF & O2 Sensor problems
- A check of the connections to the controller under the front plastic engine cover is also worthwhile
- Valve replacement recommended at 50K miles, apparently these valves can rust through from exhaust heat due to malfunction, then you can get exhaust in the intake before the MAF
- Someone posted that the check valve was a MB recall item due to early failure.

Has anyone done this change with any success? Also does anyone have a part number, official name for this part and recommended provider to purchase from? I checked Auto Parts at AutohausAZ - OEM Auto Parts - Discount Replacement Parts, Resources and Car Care Tips like I did for the MAF and could not find any parts with name similar to check valve.

Autohaus Parts for 1998 Mercedes SLK 230
Search by Car System - Select Car System

Back to the MAF Sensor

I also found more information out about the MAF sensor. You can replace this with two methods. 1) You can replace the Bosch insert only (Pic MAFSensorDetached.jpg) or 2) the whole MAF including the tube. (Pic MAFSensorAttached.jpg)

According to Bazzle’s posts all the Bosch inserts appear to have the same part number. F 00C 2G2 025. Another post suggests MB Part Number on this is PBT-GF30. Make sure you are getting an authentic MB part and not a duplicate.

If you decide to go with only replacing the insert you will need to purchase an Air Mass Sensor Torx Bit to remove it. You can find this and the Mercedes Benz MAF Sensor Insert at the following link Mercedes Benz MAF Sensor Insert.

One post however comments that the only way you can be assured of buying the genuine article is to purchase the entire MAF assembly (not just the insert) from a reputable source, such as autohausaz.com like I listed in my first post on this thread.

Entire MAF Assembly Link
Your Parts Search Returned 1 Part(s)

I still have not found any good steps on how to actually remove and clean or replace the MAF on a SLK 230. I did find some good instructions for SLK 320 thanks to Icdial.

MAF Removal and clean SLK 320 (V6) Thanks to Icdial Picasa Web Albums - Lance - SLK MAF Cleaning

Also here is a good thread about MAF Mass Air Flow Sensor that I got some of my info from. Thanks Bazzle for all of your contributions.
http://www.benzworld.org/forums/r170...s-afm-etc.html

The following is a site that provides Technical Information on R170 SLK-Class SLK Home Page. I checked it for MAF replacement and part locations but did not have much luck. I found the following schematic on the forums with a part that looks like the complete MAF sensor called B2/5 Hot film mass air flow sensor. Is this the same sensor as the MAF sensor? http://www.benzworld.org/forums/atta...ion-me-sfi.jpg

Thoughts

Should I purchase both the MAF Sensor and Check valve? Try one before the other? I know this is a hit and miss. Anyone else experienced what I went though? Also as I said from my first post please add or correct things I have stated in this thread. I also want this to be a good reference for future users with MAF and Check valve issues. Once I get the solution I will report detailed steps of what I did to fix the error codes of P0170 Fuel Trim Malfunction, (Bank 1) and P0410 Secondary Air Injection System, car turns over and will not start. Like it is being denied fuel.

Thanks for the input.

Cheers
Corey
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#9 (permalink) Old 11-18-2008, 12:56 PM
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Quote:
Originally Posted by Shecko View Post
Restating Issue

P0170 Fuel Trim Malfunction (Bank 1), P0410 Secondary Air Injection System, Car will not start just turns over, seems like it is not getting fuel.

Hey Gang,

Should I purchase both the MAF Sensor and Check valve? Try one before the other? I know this is a hit and miss. Anyone else experienced what I went though? Also as I said from my first post please add or correct things I have stated in this thread. I also want this to be a good reference for future users with MAF and Check valve issues. Once I get the solution I will report detailed steps of what I did to fix the error codes of P0170 Fuel Trim Malfunction, (Bank 1) and P0410 Secondary Air Injection System, car turns over and will not start. Like it is being denied fuel.

Thanks for the input.

Cheers
Corey
Hi, Corey.

I can't speak with experience to the MB air injection system, but if the car won't start it isn't the MAF. You can unplug it and the car will still start and run on base settings (heck,unplug it and see if it starts, if it does perhaps you have an unusual short in yours, but that would be very very rare). Fuel trim with the misfire codes tends to suggest it isn't the MAF, from what I understand the air injection system could account for the misfires.

Take care and enjoy the ride,
Greg

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#10 (permalink) Old 11-18-2008, 02:06 PM
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I get the 0170 code all the time, even if I just bought a new MAF sensor

1999 230 SLK
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