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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Mon, Dec-12-2016, 04:05:04 AM   #21
mderenthal
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Default Re: Pre-Cat O2 sensor DIY?

Just finished replacing all O2 sensors (and leaky CPV gasket while down there) and I'd estimate this job takes about 1.5 hours of actual work, and about twice that much time to figure out how to access everything. Second time through will be much easier. (I accessed the bank 2 pre-cat from underneath).

Last edited by mderenthal; Mon, Dec-12-2016 at 04:09:20 AM.
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Old Sat, Mar-31-2018, 11:27:56 PM   #22
Alex Sol
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Default Re: Pre-Cat O2 sensor DIY?

Just completed the replacement of o2 sensor and wish to add some comments from my experience.

I had bank 2 sensor 1 go and figured i'd order the two pre cat sensors and replace at same time.

There are some diy on this subject but it seems some of them were deleted.

I started with remove fan shroud which is back off the 3 plastic screws (they are just straight so no threads and easy to drop) I did find one later in the lower plastic shroud that has to be removed.

remove the strut bar with the 4 x 13mm bolts

Then the cover where you first remove the oil filler cap and the six (I only have 5) 10mm bolts.

Removed the cabin air filter and the water catch tray below it. Unhook the main power that goes to the jumper and another wire. Remove this before the cover to easily access everything.

Then carefully removed the plastic cover that covers two sensor connections but these are for the post cat 02 sensors.

The pre cat 02 sensors are connected closer to the fire wall.

Then removed the plastic shroud under car with the six x 8mm screws

Then removed the aluminum shroud with the 11 or so 16mm bolts and 3 x 8mm screws.

Then removed the heat shield that is held on by 3 x 13mm and one 10mm bolt

Removed the hose from the coolant tank, removed coolant first using a Motive extractor. Then removed the secondary air injector piece with two x 10mm nuts

Once I had all this in hand, I could remove the bank 1 02 sensor from the top with my crow foot 02 sensor tool. I have a 7pc set.

Then went underneath using the extension technique with the 'reverse' drive to loosen the bank 2 sensor. That work well and just popped then I could unscrew by hand.

Replacement was reverse.

One thing I learned is that the two sensors have different connectors only slightly and so they cannot be reversed... dummy proof except when you have two of the same sensor then you are the dummy!! so make sure to but the two different patterns.

Other tip I could add is to have the car up safely and on jack stands and jacks as back up. Don't want to die saving $60 bucks...

Hope that helps.
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Old Mon, Nov-19-2018, 06:47:31 AM   #23
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Default Re: Pre-Cat O2 sensor DIY?

Sensor Pre 1 Bank 2 is a ******* **** *.

I soaked mine in penetrator for 4 hours and couldn't get it, even with a breaker bar. I was accessing it from underneath, with the crow's foot socket (turning to the right, which is upside for lefty loosy).

I've been advised to hit it with a torch. Anyone have luck with that?

My setup was: 20" breaker bar, 20" extension, 3/8 to 1/2" adapter, crow's foot O2 socket.

Felt like I was getting good torque but it didn't budge. Sensor Pre1 Bank 1 was way easier.
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Old Mon, Nov-19-2018, 09:36:54 AM   #24
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Default Re: Pre-Cat O2 sensor DIY?

Quote:
Originally Posted by SarcastaBall View Post
Sensor Pre 1 Bank 2 is a ******* **** *.

I soaked mine in penetrator for 4 hours and couldn't get it, even with a breaker bar. I was accessing it from underneath, with the crow's foot socket (turning to the right, which is upside for lefty loosy).

I've been advised to hit it with a torch. Anyone have luck with that?

My setup was: 20" breaker bar, 20" extension, 3/8 to 1/2" adapter, crow's foot O2 socket.

Felt like I was getting good torque but it didn't budge. Sensor Pre1 Bank 1 was way easier.
This was with the manifold off: WD40, battery powered impact wrench, and 3/8 in. Offset Oxygen Sensor Wrench. Easily removes sensors with 100k+ that are seized with rust, otherwise almost impossible to remove with a breaker bar or regular wrench.


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Old Mon, Nov-19-2018, 01:13:25 PM   #25
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Default Re: Pre-Cat O2 sensor DIY?

Sometimes, using a different penetration oil works for me.

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Old Mon, Nov-19-2018, 03:48:08 PM   #26
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Default Re: Pre-Cat O2 sensor DIY?

This thread makes me glad I replaced my primary O2's when I did my headers... Sounds like it's just about the same effort to change the sensor
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Old Mon, Nov-19-2018, 04:38:00 PM   #27
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Default Re: Pre-Cat O2 sensor DIY?

Quote:
Originally Posted by L0ADED View Post
This was with the manifold off: WD40, battery powered impact wrench, and 3/8 in. Offset Oxygen Sensor Wrench. Easily removes sensors with 100k+ that are seized with rust, otherwise almost impossible to remove with a breaker bar or regular wrench.


Whoa. Impact gun? Yikes. I REALLY don't want to remove the manifolds, because I've heard that's not an easy process. So I'll hit it with a torch on Friday, and get some liquid wrench (I won't use the torch on the flammable liquid wrench, of course), and twist the extension until it breaks, or the sensor moves.

I love cars.
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Discussing Pre-Cat O2 sensor DIY? in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)