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Mini cooper o2 sensors

My daughter has an 05 mini cooper.

Fault code has shown up on the rear o2 sensor.

I’ll trying to find out if the o2 sensor are different, pre and post.

Reason I ask, the post sensor is about $100 higher than the pre, they are both 4 wire, heated and look the same. I understand o2 sensors give out different voltage, but I want to make sure this isn’t a way to get someone to pay an extra 100 for the same sensor, just by calling it a post and not a pre sensor.



There are usually differences between the two sensors. One will usually have longer wires, and sometimes a different plug so they can’t be accidentally reversed.

What was the actual code number you got? Sometimes it isn’t the Oxygen sensors that fix the problem. Sometimes the rear Oxygen sensor is telling the truth and is trying to tell you about an engine problem, while some mechanics will automatically assume the sensor is bad.

Advance Auto shows the same Bosch part number for the front or rear oxygen sensor. There is Bosch 13878, with the electrical plug on the end, for $177. There is Bosch 15730, for the front or rear, without an electrical connector on the end, for $67.
For the Bosch 15730, you have to cut the old wires, and use the crimp-on connectors to attach the wires to the new oxygen sensor. One drawback with this is the new wires are black and white. The old wires are not. Which goes to which? And two, if the splice is of poor quality, there can be future problems from that.
A DTC (Diagnostic Trouble Code) does NOT mean to shoot the messenger (the oxygen sensor). It means, “Here is a message, of something awry, that needs troubleshooting”. Using diagnostics, one troubleshoots the problem.

Added: I DO mean to imply that there are a lot of mechanics / shops who don’t troubleshoot when they should. They just use the DTC code as an excuse to just change a part.
Whatever caused the oxygen sensor to send a code, won’t be cured by changing the oxygen sensor. The fault is still in the engine. Only the messinger has been shot.

The repair shop didn’t give me the code, just this info…
=fault for failing oxygen sensor, bank 1, post catalytic coverter.
(oxyen sensor replacement cost approx 305.00)

Thanks for the info, I’ve been told the connectors do look different from the 2 sensors, but if that’s the only thing, I feel good about changing out the connector, as long as I can get the right wire in the right place, as per next post.
My understanding is 2 of the the wires is to heat the sensor and the other 2 are for the voltage output.

One wire is computer Ground
One wire is Regulated DC voltage from computer (+5 VDC)
One wire is heater DC voltage (+12 VDC)
One wire is O2 output to computer

any chance the wires are color coded?

Why don’t you call the shop and get the numerical code and post it here? It might keep you from replacing a good Oxygen sensor.

Looks like there were several codes, here’s what they told me showed up.

mrs5k 82, 80, 50 and 71
dme p2270 and 0136
zke 33 and 90
lew 0A

Now that you have posted the codes, some of the more knowledgeable members might be able to give you a better idea. I have taken you as far as I can.

I think we are being put upon. Those aren’t OBD codes, which are mandatory use. They may be some internal codes; but, they don’t help us to help you. If you can get the car to an auto parts store (Advance; Auto Zone) they may read the codes, for free. The DTC code format is: P0420, Pxxxx.

I’ll call a couple of the stores near by and see if they can read them.
If not, I’ll just have to suck it up and buy the more expensive sensor, being the post, and put it in.

If you do change the oxygen sensor, yourself, you may know someone who can cut and crimp the four wires. There is an explanation of what function each wire goes to; such as: ground; signal; power; heater. The wiring diagram for your car shows the wire colors for each function.

The DTC (Diagnostic Trouble Code) P2270 is a universal (all car makers) OBD code for “Oxygen sensor [shows a] stuck lean [air/fuel mixture], B1, S2 [post-catalyst]”. P0136 is simply, “[Problem with] oxygen sensor circuit, B1, S2”. It’s non-specific, isn’t it?
“Lean” means that there is too much Air, and not enough Fuel [Air/Fuel ratio] for the oxygen sensor to do its job (of measuring the Air/Fuel ratio and telling the engine computer).
So, in sum, the oxygen sensor may be operating normaly. Maybe, there is an air leak in the exhaust pipe where it joins the exhaust manifold; or, where the exhaust manifold joins the engine cylinder head; or, where the exhaust pipe joins the catalytic converter, may be leaking. There are gaskets at those places.
Has the exhaust been worked on: to “tune” it, or to repair it? That can cause this problem.

No, first problem started with check engine light, so I tightened the gas cap, light went off, but would come on and off now and then. Then the a/c started clacking and clunking, sounded like the clutch was engaging and disengaging real fast, then the transmission wouldn’t up shift, making the engine run real fast, around 4-5k. This all happened within a 2 week period
So, took it to get checked out.
Here’s what the shop told me…
A/C blown up, has to be replaced with compressor and drier.
The computer had to be reprogramed due to, interupted power, I changed the battery out about 8 months ago.
Post sensor bad, needs to be replaced.
Power steering fan needed replaced.

I didn’t like the prices they give me to due the work…seemed very high 2000.00.
I pulled the power steering fan off, cleaned and tested, it was just clogged up with dirt and road grime. I got a rebuilt ac compressor and new drier, so all I’m lacking to do from their list is replacing the o2 sensor, which is where I learn the price difference from the pre and post sensor.

So far, my cost in fixing the car myself has been about 600.00 v/s 2000.00

How do you know that the oxygen sensor is defective? It is most likely that the oxygen sensor is reporting a real problem. That’s its jay oh bee (job). It’s doing what it’s supposed to be doing. If you are so dead set on changing it, that’s your call.

I wanted to say the same thing, but I had to remind myself that you can lead a horse to water, but you can’t make it drink. If he is dead set on spending money on a new Oxygen sensor, there is very little we can do to stop him.

He might go out and buy an aftermarket Oxygen sensor, have it not fix the problem, and he will never know if the problem is that it is the non-OEM sensor or if the sensor was working as it should all along.

Thanks for the help.