I had the exact same problem trying to replace the post cat sensor on my '04S. Took lots of fiddling around with the connector trying to figure out which part stayed where and how to release the locking tab. Didn't help that there were other lines right over the top of the connector limiting access for my big fingers. I used a small, thin screwdriver to finally pop the lock tab.

Warning!!! I bought a supposedly OEM sensor from Atlantic British and while it looked identical, there was a difference in the connector and it wouldn't fit!!! Pissed me off royally since I had fought with the connector. Fortunately, my old sensor was still intact and I refit it and all is well now. Atlantic British sent me another sensor but it was still different inside the connector.

Eric

 

Yes, I would replace the O2 sensor as recommended. The O2 sensor is used to determine the level of Oxygen in your engine exhaust so that the on-board ECU (computer) can adjust the timing to optimize gas mileage, performance and minimize the smog pollution output at your exhaust pipe. If Mother Earth is important to you, replace the O2 sensor as recommended. Your Mini engine will run cleaner and you will definitely get better mileage.

O2 sensors are similar so you can use a universal unit that's recommended for your Mini. The major different is during the installation, you will have to modify the (2) wires to connect to your existing wire harness. Use a 22mm socket to remove (counter clock wise) and torque it down when you install the new one.

If you should fail the smog test in the near future, it's most likely because of a bad O2 sensor since your Mini has 122K miles. The mechanic will gladly replace the sensor for about $350 or you can prepare ahead and replace the sensor with a universal unit for about $90.

 

Readers should be aware that there's quite a few mentions on NAM about aftermarket sensors that fail prematurely. I had the experience of a shop replacing one of mine with a Bosch type and claiming it was OEM; it failed after one year. I replaced it with an OEM sensor (for around 250 bucks) and installed it myself (as mentioned earlier in this thread).

 

Replaced both O2 sensors yesterday with aftermarket ones from British Atlantic. I, uhm, didn't see all the references to problems with aftermarket sensors until after I'd ordered the parts. Can't tell you which aftermarket parts because there are no markings on the sensors, and I didn't see any reference to manufacturer on the site when I bought the parts. We'll see if any problems pop up.

My '04 MCS hit 100 000 miles a few weeks ago, and no SES or CE lights were on. I just figured it was time to show my MINI that I care. Also installed new plugs, ignition wires and fuel filter. And an oil change, of course.

 

I replaced the pre-cat sensor on my '03 MCS over the weekend because I was getting a P0130 code. I had never replaced an O2 sensor before. I used the NTK #25648 unit, which is a perfect replacement as others here have indicated. Rockauto.com was the least expensive source for the sensor that I could find. The repair was somewhat of a struggle, but I got through it. I cut the wires off the old sensor, and that enabled me to use a 7/8" closed end wrench to remove the old sensor. I'm a pretty strong guy, but it took all my might to break the old sensor loose, although I did not have to resort to penetrating oil and/or heating up the exhaust system. I also struggled with unplugging the wires from the old connector. It was fairly obvious how the release tab works, but the plug just did not want to come out of the connector after being hooked up for 9 years/ 150k miles. I unintentionally ripped the connector off the car, but that ended up being ok because that made it more accessible to work the connector loose. And the female portion of the connector (part of the assembly that you replace) is what is actually clipped to the car, not the male connector that plugs into it, so even if I damaged the old connector when I ripped it off, it did not matter as the old one was going in the garbage. I did not clip the new wire to the heat shield. Instead I routed it around the far side of the hoses coming down from the power steering pump reservior, as I assumed the further the wire was away from the (assumedly) hot heat shield, the better. According to the Bentley manual, the CES light should have turned off after three engine cycles, and when that did not happen I thought I might have damaged the sensor (which apparently is rather delicate), but for some reason it took five cycles on my car. Hopefully the CES light is now permanently out.

 

It helps to tap the wrench with a hammer to break things free. Not really hard, just a good, firm tapping. Maybe about half as hard as you would swing a hammer to drive a 10 penny nail into a 2x4.

 

Just wanted to say thanks for this info. I too had the same error code (P0130) and was trying to replace the pre-cat sensor, but had been trying to use an open-end 22 mm wrench. It is a tight spot and there is just not much room to swing the wrench, especially when confined to the angle of the open end. Never occurred to me until I read this post to cut the wire so I could use the box end, which allowed a much easier angle and therefore more leverage. Your post told me everything I needed to know. (I too struggled with the electrical connector - I was able to release the connector from the mount by giving it a slight twist so I could work the two halves free with a few small screwdrivers.) Thanks again!

 

I just use the open end of the 7/8 wrench and moderately whack with a 3 pound hammer until it starts to move. The impact action works every time.

 

Add me to the list of people who have trouble with separating the O2 sensor electrical connectors; in fact that is why I am here reading this thread. Getting the sensors themselves loose is no problem. But with the pre-cat electrical connector, it was different.

First, I studied the new O2 sensor connector to see how it might latch with the other side (which of course I do not have free to study). On the old sensor connector, I depressed the tab and could not pull it free by hand. While depressing the tab, I then used a screw driver just in front of the tab to pry one connector from the other; it then came free without incident.

However the connector on the business end is still attached to some sort of mounting point, and I am having trouble getting that free. Looking at the new sensor, it looks like there is a plastic "finger" on the back side of the connector that I need to pry (to my right, as I look down on the connector from inside the bonnet) to free the connector from its mount. My screw driver was apparently too long to get in there and/or had too wide a blade. But do I have the technique about right?

For those of you having trouble finding the pre-cat electrical connector, try this: look straight down between the oil filler cap and the air filter box. It is a few inches down. There are two clips (at least?) holding the sensor wire to various and sundry places as it winds its way down to the sensor. Note the way it is routed before you remove it fully so you can route the new sensor wire the same way.

One funny note: I checked the Bentley manual on this and it was beyond useless. Even the torque specs seem fishy: under "Other Mechanical Maintenance" in the Maintenance chapter, it says to torque the oxygen sensor to exhaust manifold at 37 ft-lb. Under Exhaust system in the Engine Chapter, the tightening torque table says to torque "oxygen sensors to exhaust 29 ft-lb". Part of me thinks the first one is for the pre-cat sensor, and the second one is for the post-cat sensor, but then 1) why is one torqued to a different spec than the other? 2) why does it say sensors, plural?

 

You need to use a small pick tool to pry that tab. They sell them as a set of four (straight, angle, hook, double angle) at your local auto parts store for around $5. If you don't have one, a wooden skewer or a toothpick might work.

Both sensors should be torqued the same. Good and snug and then a bit more to make sure they are tight. PS - is it even possible to get a torque wrench onto an oxygen sensor?

 

Ahh, yeah, a pick will work great. I have a set but I didn't have it with me when I was doing my preliminary investigation. Thanks for the tip!

It sure doesn't look like there is room to get a torque wrench in there.

By the way, I find your videos very useful! Thank you and keep it up!

 

I just wanted to thank you guys for the info on the O2 sensor! While I didn't replace it myself, I was wondering how it could cost $480.00 to replace. The place I tske our '02 mini to get fixed always orders from the local bmw dealer. The "check engine" light had been coming on, and the car was due for inspection. I was getting concerned about the price, so decided to check. It seems all right, if not a bit steep...but for someone who stopped working on his car once carburetors disappeared, I really had no choice. This was a sensor that was post. After replacement, my wife said she had a moment where the engine raced and it became hard to switch gears, so I have to take it to the shop again. The shop also reset the "check engine" light and told me to drive it around 75 miles to reset it. In any case, your DIY info made me feel slightly better about the price. Good day!

 

Hopefully that $480 price is for both sensors but I think I understand from your post that you only replaced the post-cat sensor? It looks like MINI charges something like $250 per sensor for the part. You can buy genuine mini sensors from online places for something like $200 each.

I chose to buy NTK sensors. I paid $99 for each sensor. They came with the MINI connector already installed so no splicing necessary. I had to shop around to find that price, as most places want $150-170 for the NTK sensor.

 

I have a 2009 MINI Cooper S that need the upstream O2 sensor replaced. I sourced out the part at O'Reilly Auto Parts and the only option they had was a BOSCH 17112 at $181.99. Do I have any other options, or do I have to stick with BOSCH? Any help wouldn't greatly appreciated! Thanks in advance.

 

You want to stick with OEM supplier for upstream O2 sensors or engine will run funny. But you can get a lot cheaper than your local parts store: https://amzn.to/2L5IcAr

 

Public Service Alert:
Do NOT buy parts from ROCKAUTO. I ordered an O2 sensor for my 2010 Clubman S. They showed an exact fit, which was a Bosch 17112; 11-78-7-549860-00. The part arrived, and the box showed the above numbers - exactly what I wanted. I installed the part, but the check engine light came on within 30 miles. I finally discovered that the O2 sensor had totally different numbers on it - was made to fit a Peugeot of some kind. RockAuto is impossible to get hold of. (Probably by design). I finally replied to an email that I had received that confirmed my payment to RockAuto. They said I could use a Manufacturer's warranty to get the part replaced. But the dumb asses never recognized, or admitted, that they had sent the wrong part. I would have been more satisfied if I had just flushed the $113. down the toilet.

 

Jepz, it's not a hard job, but only a tad difficult to reach/tight space. The lambda tool is absolutely necessary

 

With two sensors and one service engine soon light, how do you know WHICH sensor to change?

 

Error messages will be like:

Bank 1 Sensor 1 or Bank 1 Sensor 2

Sensor 1: precat lambda sensor (the hard to reach sensor)
Sensor 2: after cat lambda sensor (the easy to reach sensor)

Extra info
Last time I will buy a VEMO sensor. I got the p0036 error (heater control circuit bank 1 sensor 2) error, even though I changed the sensor not too long ago (june 2020). I replaced it with a Magneti Marelli O2 sensor, which I also used for the front sensor. Also the CEL light kept burning, even after clearing it with Torque Pro. I needed to clear the code using INPA before the CEL was gone.

 

Got P2096 code. Throwing the dice that it's a O2 sensor.

 

Yep looks like post cat

 

Too lean. Make sure you don't have any air leaks.

 

so none of the WMW links work, anyone know the tool that was linked?

 

Sounds like it’s a normal 22 mm open end wrench.

 

vendor websites
Detroit Tuned - https://www.detroittuned.com
ECS Tuning - https://www.ecstuning.com
Outmotoring - https://www.outmotoring.com
WayMotorWorks - https://waymotorworks.com
Mini Mania - https://www.minimania.com/index.cfm
Cravenspeed - https://www.cravenspeed.com

bmw/mini parts catalog- https://www.realoem.com

you might want to save these to your bookmarks since you can’t seem to be able to use the internet. These 02 sensors sockets can be found on Amazon too. Like for real, bring back 3 threads for a socket. Google.com works too, just saying.