07-up MINI Cooper/Cooper S (R56)
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DTC for Heating Circuit of Downstream O2 Sensor

Old 07-30-2018, 08:24 AM
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Join Date: Apr 2017
Location: Houston, Texas
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Default DTC for Heating Circuit of Downstream O2 Sensor

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. Yes, I know that my Clubman is an R55, but I figure there are more people who use the R56 section who may have answers.

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.
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