Hello, I have been trying to track down a rich condition for ages and am at my wits end. I replaced the downstream O2 sensor several months ago and recently replaced the HPFP which was completely failing. I was hoping the HPFP issues would resolve the rich condition, but it has not. After clearing codes and driving around 2 or 3 times, these are the codes that always return.

The generic codes only appeared on my generic scanner, but I have a Foxwell NT530 as well which provided the MINI specific codes. So far as I can tell, except for the P10EE (which I cant find any info on), the MINI codes and generic codes match up.

Generic OBD Codes:
P0036 - HO2S Heater Control Circuit Bank 1 Sensor 2
P0141 - O2 Sensor Heater Circuit Bank 1 Sensor 2
P0172 - System Too Rich Bank 1
P10EE - Unknown

MINI Specific Codes:
2BC1 - Mixture Control: Fuel-air mixture too rich
2D11 - Oxygen sensor heating after catalytic converter, activation: Line disconnection
2D13 - Oxygen sensor heating after catalytic converter, function: Internal Resistance too high

All that said, the lack of any additional codes makes finding the cause of the rich condition awfully difficult. Allegedly the downstream O2 sensor doesn't cause fuel mixture changes, but I don't know if that's actually true. Even so, here are all the things I have confirmed:

• New downstream O2 sensor (allegedly OEM, its FAE brand)
• New HPFP (had low fuel rail pressure)
  • Reset adaptations after install
  • Had hoped this was causing the rich condition
    
• O2 sensor circuits and resistances test normal so far as I can tell (checked months ago, not recently. Code was still present at install)
• All proper voltages to O2 sensor and MAF sensor
• MAF shows normal operation, no codes, proper voltages and resistances
• Downstream O2 sensor voltages go up and down properly - though basically stays between 0.75 and 0.81 volts (rich condition) while driving
  • properly drops to 0 volts during coasting and decreases when idling
    
• I tested the injectors for leakage by disconnecting them from head, connecting to them fuel line, and engaging the ignition (engine off) with a blue shop towel under them and there were no signs of leakage
  • I have no idea how reliable of a test this is

Overall, I am not sure what else to check and other than the rich condition, every component seems to be working normally. What can I check? What else might cause a rich condition without causing any other codes? Can a downstream O2 sensor cause this issue? Would a faulty heater circuit of all things cause this? Anyone know what this P10EE code is?

 

For the downstream O2 sensor, check whether the heater wires are getting proper voltage and ground from the DME. But as you mentioned, this would not directly cause the rich condition.

For the rich condition, have you verified that the engine is actually running rich? Do you smell unburnt fuel in the exhaust when the engine is fully warmed up?

Post live data streams from the upstream O2 sensor to determine whether it's malfunctioning. Then go from there.

 

I had a rich condition on my R53 after installing some aftermarket injectors. The didn't leak, but they sure didn't spray right. Have you installed new aftermarket injectors recentlhy?

You are correct in that most cars use the upstream O2 sensor to control the pulse width of the injectors, but the MINI N18 will also use the downstream sensor for fuel trim adjustments.

With your Foxwell tool, go into the OBDII menu (not the MINI menu), and pull up your fuel trims. To help you isolate the problem, pull the short-term fuel trim and long-term fuel trim at idle, 1500 RPM, and 3000 RPM. Post your results.

Did you replace the downstream O2 sensor with an OEM supplier sensor? I've found that N series engines don't like aftermarket sensors. Case in point, I thought NTK was the OEM supplier for my N12 engine's upstream O2 sensor; the DME was setting codes for this sensor. The I found out the OEM upstrream sensor was Bosch and NTK was the OEM for the downstream sensor. One installed a Bosch upstream sensor, my problem went away.

It sounds like your downstream sensor is working properly, but you need to fix the heater fault issue. The downstream should run above 450 mV and I see mine run at a steady .720mV. Yes the signal will change during hard acceleration and deceleration, but at a steady state, .750mV is good.

 

Stock Fuel Injectors - O2 sensor is allegedly OEM (FAE brand) - Long Term Fuel trims hover between -23% and -30% (very high negative) and the short term fuel trim bounces around between -5% and +5%, nothing crazy there. You mention for an N18 the downstream O2 might adjust fuel trims, but does that sound likely in this scenario? It seems the only issue is the heater circuit, but even if that was an issue at start up, things should normal out (fuel wise) after the engine runs for a few minutes and the O2 sensor is properly warmed, no?

This is the O2 sensor I bought: https://www.ecstuning.com/b-fae-part...787548961~fae/

 

Your OE upstream O2 sensor is Bosch; OE downstream is NTK. I would install the correct O2 sensor before I went any further. You can get the NTK sensor at Rock Auto for a really good price.

-23 to -30 LTFT is very rich. Negative numbers means the DME is pulling fuel away. Remember the job of the LTFT is to keep the STFT as close to zero as possible, but your LTFT is maxed out (on the negative side).

Not might adjust fuel trims, it does adjust fuel trims according to BMW's TIS.

Who knows what the logic circuits are doing in the DME when it sees a faulty downstream O2 sensor heater; keep in mind this is German, and Germans don't like it when things don't work.

You also forgot to post the fuel trim numbers at the various RPMs

 

For code 2BC1...


Look up P10EE here. It may be a code for high fuel pressure.

 

I got some Live Data from my upstream O2 sensor and would like your thoughts. Its a wideband sensor, so my understanding is that it won't have that normal repetition of jumping between 0.1v and 0.9v. I couldn't find good info on what the voltage SHOULD be, but if the "reference" field means anything on my Foxwell then perhaps its still too high? The commanded fuel looks like its maxed out? Anywho, the voltage seems to remain steady at almost 1.00 volts regardless of engine RPM. It fluctuates a TINY amount, but the graph is otherwise fairly steady. Based on the screenshots of this Live Data, and knowing its a wide-band sensor (not a normal narrowband), does it seem like the sensor might be faulty (even though there is no code) or?

Sorry if these images are enormous. I dont know how that works lol.

 

^What he said here.

It might be that the fuel pressure sensor or high pressure fuel pump is intermittently going out? Might want to bookmark that code site, as it can help determine service path when codes get stored.

 

I went through something like this recently with my Volvo where my LTFTs were almost pegged rich, but the Upstream O2 AFRs seemed to stay in the mid 14s unless on decel.

No codes, but had a gut feeling the O2 should be moving around.
After replacing, it seems to act much more like expected.

I'd try to get an upstream O2 (or STFT, or upstream O2 voltage) graph and see if it's lazy looking. If it does, fire a new OEM sensor at it.

 

Its not - the Fuel Rail Pressure is always normal (I also just recently replaced the HPFP). For that P10EE code, you have to check the ECU variant carefully. Looks like for these MINIs, its a DME communication issue. Which alone, is super unhelpful haha.

 

I was off base with that data above I think. Was looking at the wrong live data. Going for a short drive, the upstream O2 sensor mostly stayed around 1.5v, but had some short moments where it might dip up and down, most staying close to 1.5, but it dipped down to 0.8 volts once and up to 2.2 volts once or twice. I would wager the sensor seems to be working normally otherwise though.

Anyone know how I can test for faulty injectors? I hate to throw parts at something without being sure, but I can't figure out how to confirm if they are working properly or not lol.

 

Well for anyone wondering or for future people that find there way here with similar issues, I replaced all 4 of my fuel injectors which did not resolve the problem. I then did some further testing on my trims and voltages for my O2 sensors, and found that rather my upstream sensor was plugged in or NOT, all of my fuel trim data was exactly the same, along with my downstream sensors output voltage. Needless to say, I fully expect that replacing the upstream sensor will resolve my rich condition as it would appear that it wasn't doing anything anyways haha.

I'll post another update if this doesnt resolve my issue still, somehow.

 

That's some excellent troubleshooting.

You may want to continuity test the upstream O2 sensor wires before replacing the sensor, though I think you're on the right track.

Also, did you make the upstream O2 sensor readings with the engine fully warmed up? Most ECUs ignore upstream O2 sensor data when the engine is cold.

 

You are correct; the N18 uses a wideband O2 sensor upstream. The downstream sensor is a narrow band.

You are also correct in that you will not see the voltage switching form lean .2 volts to rich .8 volts. Notice in your picture you have Sonda Lamda Current, bank 1, sensor 1. That's the one you want to graph. When you are troubleshooting a wideband sensor, the voltage doesn't switch; the current switches. Also, with a narrow band sensor, a .8 volt signal will indicate rich, and a .2 volt signal indicates lean with .45 mv being the switching point (below is lean; above is rich). Now with a wide band, press F2 and watch your Sonda Lamda Current. Make sure the engine is running at about 2000 RPM. Then have someone add propane to the air inlet; this will make the mixture rich and the current will drop. Remove the propane and the mixture will switch back to the lean side and the current will rise. This is how you can easily tell if your upstream sensor is functioning properly. If you are running rich and the upstream sensor is fixed rich (rich condition condition; lean command). You will see a negative current from the O2 sensor and the current will not rise when you add the propane. If the current rises when the propane is added, your O2 sensor is fine and something else is causing the rich condition.