How to clean MAF?
 

Although my 2001 CLK320's CEL has been on 6 months, the runs normally. However, with a CEL on, won't pass state inspection in MA next month. Codes are P0170 and P0173.

I have searched and read all the discussions and decided to try cleaning my MAF last weekend.

I removed the MAF and then took out the sensor insert to clean. The only thing visible was an electronic part that was a wire with a tiny glass cylinder in the middle (diode or termisitor). What I could not find was the coiled wire, metal plates etc. that have been discussed.

At the end of the sensor insert, there were some small square openings and there appeared to be additional metal objects inside. However, the openings were to small to get at them. So I attempted the cleaning by submersing the sensor in a container of denatured alcohol and shaking it. Reinstalled the MAF and the CEL remains on (manual says that it will go off after 3 complete cycles of normal operation).

The MAF is MB part # 112 094 00 48, Bosch # 0 280 217 515. BTW, the Bosch web site shows the # as 0 280 217 516 (w/ the word "new" added).

At the end, were the small square holes were, it appeared that there might have been a removable cover section. Since it didn't come off with reasonable force....the did the alcohol bath.

Any advise as to how this could have cleaned the sensor?

Cleaning a MAF is not recommended. It is not a fix for a bad MAF. MAF's are throw aways when they fail. Cleaning a MAF like you did will ruin it if it was good in the first place. MAF's are VERY delicate and are easily damaged by handling. They are a consumable part. Buying an aftermarket or a MAF off of EBay is also a risky proposition.

buy a replacement first before you attempt to clean the old one

I do know people who have cleaned the MAF and it worked, unfortunately I don't remember what they used. I think it might have been a spray as you suggested. "contact cleaner?"

I also know my 87 corvette had a system to burn off the maf on start up to insure it was clean. So if the corvette came with a system to clean it from the factory there must be some method that works. Given you will have to buy a new one any I would try it. My suggestion would be an electrical circuit board cleaner that flashes off leaving no deposits. I have cleaned many circuit boards that were under water in Katrina and they still work. So give it a shot. :) Jim

Spray QD (Quick Dry) Electrical Cleaner directly on the sensor wire (an extremely fine and sensitive wire found within the MAF sensor); let dry for a few minutes; then reinstall. I have applyed this to various vehicles with great success. Do not ever apply any cleaner with a cotton swab as some suggest. A couple of quick spurts should do the trick. Good luck.

Who makes it?

Who sells it?

TIA

Any Electronics Supply store. :)

I started throwing P0170 / P0173 codes on my R129 (SL500). I suspected either a fuel issue (filter/pump/regulator) or the MAF. Since the MAF depends on thermal transfer from the air to measure the density, even a slight build up of dirt/dust will significantly change that value. So I popped the MAF out with no tools (it's held in by a plastic clamp and a small steel spring tab). I cleaned it with CRC contact cleaner and dried with with a low flow nozzle from my compressed air source. I replaced it, reset the MIL/codes with my scanner and drove off. At first, the P0170/P0173 codes reappeared as "pending", but after a little driving for the ECU to re-optimize the fuel adaption values and another reset, all is well. BTW, the slight time delay for the ECU to re-adapt is why MB some techs insist that they must reset the adaption values after a MAF sensor repair. In reality, the ECU will take care of itself, but they want to avoid even the possiblity that you will come back with the MIL light on.

Anyway, just my experience.

- FD

MAF sensors are electrical and typically don't fail. They get dirty from air filter fibers, dust, pollen, oil (if you use a wet filter) etc..

When this happens, the sensor gives an inaccurate reading to the ECU...resulting in a rich mixture, loss of power and excess emissions.

At my last dealer 'B' service, I asked why the air cleaner has never been changed in 40,000 miles. The service advisor said they check it and clean or replace as necessary.

Thought it was time to replace, so I bought a new filter When I went to replace it...I found a pinched area on the outside rubber frame of the old filter (so I think crap has been getting by). Would have expected dealer service to know how inspect an air cleaner.

My initial question, that starting this thread, was I knew something more was needed to clean the sensor than just putting it a container of alcohol and shaking it.

Turns out, CRC Industries actually makes MAF sensor cleaner.

http://www.crcindustries.com/auto/co...x?S=Y&PN=05110

Just bought a can (sold at PePBoys and NAPA) for $5.99 (special at PePBoys until end of month).

It comes with a thin straw...so you can easily clean the hot wire and plate.

On a 2001 CLK320, book saids that the CEL will turn off after 3 complete cycles (guess that means cold starts) of correct readings.

It's worth a try (invested $6 for the can of cleaner and $10 for a set of TORX security bits). I bought the TORX set at Advanced Auto Parts (who will also scan your OBCII error codes for free). Might be able to buy just the required T-20 size bit at Sears.

I'll let you folks know the results.

It's been a week and over 100 miles and the CEL is still on.

I did a lot of research on the topic and cleaning the MAF often works.

When I changed the air filter last summer, I found a pinch in it's rubber frame (gap that would allow unfiltered air through). During all my A and B dealer service, they said they inspect the filter and clean or replace as necessary).

I suspect that the MAF parts got a pretty good particle blasting.

MY codes are P0170 and P0173. With CEL on car won't pass inspection in June.

Trying to decide if I just buy a new MAF for $300 or have a shop diagnose and repair.

Just for information I looked up the MSDS and find the cleaner is essentially hexane in spray form.

Installed a new MAF and CEL still on (even though 9 out of 10 times codes P0170 and P0173 = MAF).

Any thoughts on next steps?

Ideas on how to best detect vacuum leaks?

did you have the codes read again? you might want to try to erase codes too.

Did any of notice a regain of power after cleaning the MAF? I have no code for the MAF but it has been in the car for 63k miles.

Good news.

Ny CEL was off this morning.

Manual said the CEL would turn off after 3 cycles of normal readings. Maybe a cycle is a day and not cold starts as I assumed. Turned off on day 4 which involved a dozen or so cold starts and about 50 miles.

Paid $265 delivered (dealer wanted over $400). After reading some of the horror stories about EBay, I found the best price for a new MAF at:

http://www.autohausaz.com/

They returned my telephone call within 1 hour, assured me it was a new Bosch MAF, would ship that day etc.. They even send me email to confirm shipping with UPS tracking info..

Although the CEL tyrned off....went to AutoZone and the codes are still in memory. Have to get a MA state inspection sticker this month.

Anyone kknow if those codes evently go away?

After changing the MAF....the CEL turned off after days. As the book said, needs to go through 3 cycles (cold starts) w/o finding a fault.

Now the fun began.

Even though the CEL was not lit, I went to Auto Zone and their scanner showed that the P0170 and P0173 codes were still in memory. Called Mercedes USA and their technical product specialist insisted the only way to clear the codes was for the dealer to erase them with the STAR tool (dealer wanted $120). I begged to differ and after driving around 140 miles, went back to Auto Zone and they were gone.

Thought it was safe to get the MA state inspection and I failed. The reason was that 2 of the OBDII sensors (catalitic and secondary air injection) came up as not ready. Called Merecedes USA and asked what the drive cycle to render all the sensors ready needed to be. Again they said the only way was bring it to the dealer. Told them I would not ever go to the dealer because they broke it to begin this saga (after last B service found a 1/2" pinched gap in the air filter's rubber frame, which allowed dust, pollen though to the MAF). Actually think the unit was sand blasted which is why the cleaning did not work. Drove 400 miles more and today got my state sticker (all OBDII sensors in ready mode).

Clarification please....
 

Wasn't the OBDII scanner able to clear, as well as read the codes? I have a cheepo scanner and it clears the codes.

Although most scanners should be able to clear the codes, the store policy did not allow them to do this.

As described in the owners manual, the CEL and codes will clear after 3 cycles (cold starts) w/o any faults being present.

The I gotcha is that then there is a pending state where OBDII sensors are 'not ready' to monitor. They become 'ready' after a drive cycle of several hundred miles.

I failed MA inspection, even though I had no CEL or codes present, because 2 of the senors had yet to reset to the 'ready' state. Hand scanners do not see the ready or not ready sensor status.