[sherazkn]

Originally Posted by BadContrakt

2008 N54
Catless downpipes installed a few weeks ago
Tuned MHD stage 2

I reinstalled the front O2 sensors and all is well there
I did not reinstall the rear sensors, instead, I bunged them shut with the provided threaded bungs.

My coder tells me he coded out the rear O2 sensors. I drive it. CEL comes on. Hmmm. He checks the code and it's for both post-cat O2 sensor heaters.

The car is not throwing a code regarding emissions, it's throwing a code for faulty heaters. What's the right move here?

I'm getting these codes, I was wondering if anyone could help, I couldnt found anything to get rid of these.

- DME: active codes -
2C9C - DME: Oxygen sensor heater before catalytic converter: Activation.
2C9D - DME: Oxygen sensor heater 2 before catalytic converter: Activation.
2C9E - DME: Oxygen sensor heater before catalytic converter: Activation.
2C9F - DME: Oxygen sensor heater 2 before catalytic converter: Activation.

[dpaul]

Originally Posted by sherazkn

I'm getting these codes, I was wondering if anyone could help, I couldnt found anything to get rid of these.

- DME: active codes -
2C9C - DME: Oxygen sensor heater before catalytic converter: Activation.
2C9D - DME: Oxygen sensor heater 2 before catalytic converter: Activation.
2C9E - DME: Oxygen sensor heater before catalytic converter: Activation.
2C9F - DME: Oxygen sensor heater 2 before catalytic converter: Activation.

2C9E,F are for AFTER cat sensor heaters

Check Fuse F04 - it supplies all four sensor heaters

https://www.newtis.info/tisv2/a/en/e...ontrol/otwHfc8

It's a 30A fuse located in the engine compartment (probably - guess based on your stated model year).

https://www.newtis.info/tisv2/a/en/e90-323i-lim/SNEe0ZE

[sherazkn]

Originally Posted by dpaul

2C9E,F are for AFTER cat sensor heaters

Check Fuse F04 - it supplies all four sensor heaters

https://www.newtis.info/tisv2/a/en/e...ontrol/otwHfc8

It's a 30A fuse located in the engine compartment (probably - guess based on your stated model year).

https://www.newtis.info/tisv2/a/en/e90-323i-lim/SNEe0ZE

Thankyou!! So it did turn out that iw was the fuse, but when I started the car it blew again right away, i know the issue now and it doesnt bother me but do you know why it might blow again? Like is there something I could check step by step?

I'm guessing I should check my downpipe wires if they're plugged in or maybe melted and touching other wires. Any advice would be helpful.
Thanks

[dpaul]

Originally Posted by sherazkn

Thankyou!! So it did turn out that iw was the fuse, but when I started the car it blew again right away, i know the issue now and it doesnt bother me but do you know why it might blow again? Like is there something I could check step by step?

I'm guessing I should check my downpipe wires if they're plugged in or maybe melted and touching other wires. Any advice would be helpful.
Thanks

I'd first unplug the O2 sensors and use a multimeter to check the resistance of each sensor heater individually. Should be 5-10 ohms. A short in any of them (zero ohms) could cause the fuse to blow.
Here's the connector pinout for the pre-cat sensors:
https://www.newtis.info/tisv2/a/en/e...i-lim/CT8vHPzV
Measure between pins 3 and 4.
Here's the connector pinout for the post-cat sensors:
https://www.newtis.info/tisv2/a/en/e...i-lim/CTBBhnIn
Measure between pins 1 and 2

F04 also supplies the crankcase breather heating element (which has a significant failure rate in N54 engines, shorting and melting down. Don't know if that is also the case for N52) and the radiator shutter drive unit, so I'd check those as well after unplugging them.

https://www.newtis.info/tisv2/a/en/e...ne-oil/oXDCoJm

https://www.newtis.info/tisv2/a/en/e...ontrol/h5KARPw

If none of those test reveal a culprit, then I'd unplug sensors, breather heater and shutter motor, remove the fuse F04, determine which is the fuse terminal NOT connected to 12V, and check the resistance from that one to ground. Again, zero is bad, indicating a short in a wire. Hope that it's just a device, not the wires.

[sherazkn]

Originally Posted by dpaul

I'd first unplug the O2 sensors and use a multimeter to check the resistance of each sensor heater individually. Should be 5-10 ohms. A short in any of them (zero ohms) could cause the fuse to blow.
Here's the connector pinout for the pre-cat sensors:
https://www.newtis.info/tisv2/a/en/e...i-lim/CT8vHPzV
Measure between pins 3 and 4.
Here's the connector pinout for the post-cat sensors:
https://www.newtis.info/tisv2/a/en/e...i-lim/CTBBhnIn
Measure between pins 1 and 2

F04 also supplies the crankcase breather heating element (which has a significant failure rate in N54 engines, shorting and melting down. Don't know if that is also the case for N52) and the radiator shutter drive unit, so I'd check those as well after unplugging them.

https://www.newtis.info/tisv2/a/en/e...ne-oil/oXDCoJm

https://www.newtis.info/tisv2/a/en/e...ontrol/h5KARPw

If none of those test reveal a culprit, then I'd unplug sensors, breather heater and shutter motor, remove the fuse F04, determine which is the fuse terminal NOT connected to 12V, and check the resistance from that one to ground. Again, zero is bad, indicating a short in a wire. Hope that it's just a device, not the wires.

Thanks so much for your help! turns out when i was putting in my catless DP's in, i routed my new oxygen sensors in such a place where both pre cat sensors were getting hot.
It got so hot that the material in a small area melted all the way and exposed a couple wires in both sensors, causing a short.
To fix this i just soldered the exposed wires and taped them up with electrical tape then put them in a high heat wire loom, put my car back together and viola! no more SES or hidden codes!

Again thanks so much!

[Murta94]

Hi im having an issue with fuse 79 for the breather heater and the o2 heaters that blows constantly even though i unplugged all 4 sensors and the relay for the breather heater. Stripped the plastic pipes form the wiring to the lower sensors but couldnt see any damage to the cables. The car is a 325i 2007 between the months 03 and 09. Any idea what might be the issue?