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Old 06-20-2010, 09:26 AM
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bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
 
Join Date: Mar 2008
Posts: 22,064
Mein Auto: 02 BMW 525i M54 auto 130K
Removing and cleaning the MAF sensor housing on the I6 E39 (Bentley notwithstanding)

As the first step of an intermittent high-altitude P0174 too-lean OBD-II DTC error with fuel cutoff, I followed the Bentleys to remove & clean the "Siemens MS 43.0" MAF sensor housing on a 2002 525i and, in hindsight, I wish I hadn't because a few simple but critical steps are missing from the Bentleys.

This is what the Bentleys, page 130-29, say to do:
- Loosen intake boot clamp
- Disconnect harness connector
- Release clip from air-filter housing
- Remove MAF sensor housing
- Installation is the reverse of removal

In a perfect DIY world, this is what I needed to do on the 2002 I6 E39 (in hindsight):
- Remove 10mm bolt holding air filter housing rigidly in place
- Loosen intake boot hose clamp with a flathead screwdriver
- Press down on spring-loaded wire on harness connector to pull harness connector off the MAF sensor housing
- Release two clips from the air-filter housing with a screwdriver
- With force, compress intake boot rubber and push away from the MAF sensor housing to disconnect MAF sensor housing from the intake boot
- Lift up on the now loose air-filter housing and wiggle as you pull the MAF sensor housing out of the air-filter housing
- NOTE: Some people recommend pulling the engine air-filter housing away from the headlight assembly (see DIY in later threads below).
- Remove the MAF sensor housing and clean with hexane spray (15 good wet spurts of CRC MAF Sensor Cleaner)
- Allow the MAF sensor to dry thoroughly (it won't take long because the hexane evaporates in a minute or two)
- Installation is the reverse of removal

Following Bently, this is what I actually did on the 2002 I6 E39 (in error):
- Loosened intake boot hose clamp with a flathead screwdriver
- Used a screwdriver to pull up on the spring-loaded wire on the harness connector
- In a split second, that wire disengaged and ricocheted across the cluttered garage
- Immediately I wished the Bentley had said HOW to remove that spring-loaded harness clamp!
- Spent at least a half hour looking for that missing airborne spring clip, almost giving up on the task
- Released two clips from the air-filter housing with a screwdriver
- With force, tried to compress the strong intake boot rubber to push away from the MAF sensor housing to disconnect MAF sensor housing from the intake boot but succeeded only in distorting the soft hose-clamp steel
- Doublechecked that I was on the Siemens 43.0 MAF section (which is what a 2002 BMW 525i would be according to the chart on page 130-2).
- Read the Bentleys over and over, wondering what was missing (finally realizing they're discussing & picturing a slightly DIFFERENT setup!)
- On my own now, I loosened both spring clamps further downstream on the intake boot intending to remove intake boot, but also failed as it's wedged in there tightly
- Finally decided to remove the 10mm bolt holding air filter housing rigidly in place (so that I could wiggle the air cleaner housing a bit)
- Lifted up on the now loose air-filter housing and wiggled and pulled the MAF sensor housing out of the air-filter housing
- Held the MAF sensor housing in one hand and sprayed 15 times with hexane spray (good wet 5-second spurts of CRC MAF Sensor Cleaner) making sure to clean both protection screens and the all-important sensor in the center of the MAF housing.
- Allowed the MAF sensor housing to dry (it only took a minute and I let it sit for 10 minutes just in case while I fuddled with the harness clip trying to put it back together after it went airborne.
- Installation is the reverse of removal

Attached Thumbnails
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Name:	bentley_chart_page_130-2.jpg
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Attached Files
File Type: pdf crc_maf_mds.pdf (49.7 KB, 627 views)

Last edited by bluebee; 06-21-2010 at 02:29 AM.
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