My 2010 Clubman S has 110,000 miles on it. The car always starts up immediately; runs great; gets good gas mileage; and drives very well. The car has very good power. Never misfires. The turbo functions well. The engine does use a quart of oil in about 1,200 to 1,500 miles.

But I cannot get rid of the "check engine light". Only one code shows up: The Heater Circuit for the Bank 1, Oxygen Sensor 2 has a fault. My scanner gives a factory code of 2A53. Auto parts stores get P0036. When I got the car, it had, I think, a Bosch 7-548961-80 sensor, but who knows how much mileage it had on that sensor. So I replaced it with a cheap after-market O2 sensor. The light still came on after maybe 50 miles, which was worse than the original one. Somewhere I read that NTK sensors worked well, so bought a 25198 sensor and installed. The CEL came on before I got out of the driveway. Same code 2A53. Over time, I have erased the codes quite a few times as I tried different possibilities. Seems the problem is happening more frequently lately.

To test the heater circuit, in installed a 12 V. test light onto the two white wires in the harness. Upon starting the engine, the light flashes on and off repeatedly, and occasionally stays on for a while. From this, I am thinking the wiring to the heater has continuity, and any fuse is OK. So I have the following questions:
1. Surely all three of the O2 sensors are not all bad. But rather something else is causing the problem. Is this logical?
2. Does the heater light coming on, assure that the heating circuit is functioning properly? Should it flash?
3. Which fuse is backing up this circuit? Is it under the hood? Inside the passenger footwell? What amperage?
4. I checked the resistance of the heater within the O2 sensors and all three were about 5.3 to 6.8 ohms. Seems fairly consistent. At least they are not open circuited. Otherwise does this mean anything?
5. Any other advice in order to solve this problem?
Thank you all so much for the help. This is driving me crazy.

 

I have checked all my wiring back to the ECM. All seems well. A Service Tech at a Mini dealership told me that the resistance across the O2 heater terminals (1&2) should be 0.4 ohms. I had been getting around 6 ohms. I have not read a spec like that, however the guy seemed quite confident in his answer. Anybody know what the resistance should be?

After resetting the 2A53 code, I can start the car and drive for some time without a CEL. But upon the second start, the CEL either immediately or very soon comes on.

Any info about the specs for the O2 sensor will be greatly appreciated. Many thanks.

 

I suspect that my downstream O2 sensor is not getting the proper voltage to make it heat up properly. When reading live data, this sensor stays in Not Ready mode forever. The upstream sensor gets ready within a minute or so.

Now I wonder if there is a fuse or relay that could be at fault, or ..... is the problem within the ECM? I still am not sure if, or where, any fuse is to protect this circuit. Ditto for a relay. Anybody have some ideas? Thanks.
Bill

 

I checked the recepticle that plugs onto the O2 wire. The two white wires are for heating of the O2 sensor. The first one supplies a constant Battery + Voltage to the O2 heating circuit. I discovered that the 25 amp Fuse #2 in the under the hood fuse box, drivers side, protects this circuit.

The ground for the O2 heater is apparently made through the ECM, and it cycles with a variable amount of ground in order to actuate the heater. But the heater never really gets hot since this circuit never really makes much of a ground at all. I suspect the ECM is at fault, but I don't know for sure.

I still wonder if there is a loose or corroded connection that is causing this, but do not know where to look. Really need some advice here guys. Anybody?

 

Sorry I've never dealt with this, but my downstream is throwing a code too so I might have to. So you're saying one of the white wires is always positive and the other white wire is an intermittent ground?....and that's why your test light is flashing? Have you put the test light on the plug for the other (upstream) sensor to see how it behaves? Maybe the pulsing is normal.

Edit: This article says if the test light is lit or pulsing, it's the ECU trying to operate the heater:
https://www.autoserviceprofessional....t-code-is-real

 

csq33r:
Thanks for the excellent article. Most informative I have read. You are right about the Battery volotage being supplied to one side of the heater circuit, and the intermittant ground being applied to the other side. I used a small bulb plugged into the two recepticles on the harness. Started the engine and the bulb comes on and off.

I used an ohm meter to check between the ground side of the harness (for the O2 heater / i.e. the other white wire) and get a variable ohm reading from almost open circuited to perhaps 33 ohms and back to open circuited again and variations of that cycle. I would have expected the PCM would give a momentary reading of near 0.1 ohms, as if there were a solid ground. Which makes it understandable as to why the O2 heater never gets hot.

After reading the description in your article, about the PCM comparing resistance figures to determine if the heater is up to temperature - it makes me wonder if the Stealership may have been right about only the MINI sensor will work for sure. I just hate to pay $310.plus tax, to run an experiment.

 

I wonder if an 02 sensor simulator might solve the problem. This guy got his car to pass emissions using one. https://www.instructables.com/id/P04...imulator-Hack/

 

I've seen a few threads where people replace the sensor and the code comes back....so they replace the front one too and it doesn't solve the problem.

 

Well, I was about to decide that my ECM was faulty, so I found a wrecking yard that has several Mini Coopers. Of course the numbers need to match, and I had not removed mine yet. So I checked all wiring again, and could not find an open, frayed, or loose terminal anywhere. I removed the ECM, but the wrecking yard did not have an exact match.

So I decide to give up for now, since I need to drive the car, and re-installed the ECM and connected all the plugs. Erased the 2A53 code. Drove the car with the scanner reading live data. Now the post cat O2 sensor had never shown to be "Ready" before, but after a few minutes it did show "Ready". But after maybe 15 minutes there comes the CEL again, but this time it showed code 2A56, which is for the "functioning" of the sensor, rather than the "activation" as was code 2A53. Which to me, means that the heating circuit of the O2 sensor itself, may be faulty. Now I happened to have the old Bosch sensor installed which may have a 100,000 miles for all I know. So I installed the NTK sensor that was almost new. Before, it almost immediately showed a CEL. But this time it has not so far, and shows to be "Ready" within a minute or so. My hopes are that my problem may be solved.

But why would it? The only variable was that the ECM was out of the circuit for several hours. I had unplugged the harnesses before to check for corroded connections, but then plugged them back in within a few minutes. IS IT POSSIBLE THAT THE ECM CAN RESET SOME PARAMETERS, BUT REQUIRES QUITE A BIT OF TIME TO DO SO? Right now, I have little faith that everything is fixed, but time will tell. I sure would like for an expert to chime in with any knowledge about all this. PLEASE anyone !!!!

 

Well the CEL stayed off for about a week, at which time I sold the car. Also, the buyer has not called about the check engine light. No proof that the car is fixed, but no word that it is not fixed either.
* As I said before, disconnecting the ECM and leaving it unplugged for several hours, seemed to make a difference. Everything responded differently after that was done.
* Also, I did a "drive cycle" that may have helped. Replaced the O2 sensor when the car was stone cold. Started the car; let it idle for a couple of minutes; drove off gently and ran consistently at about 25 MPH for 15 minutes without stopping; then sped up to 40 - 50 MPH - never hitting 60 MPH, and ran for another 15 minutes; then back into the driveway, shut the car off, and let it sit overnight to totally cool off.

Hope this helps someone out.