535t

Hello there,
let me introduce myself, i have a 2008 535 XI and I have been reading on this forum for a long time.

this is my first time posting, and I sadly start with a request for help to this very knowledgeable community.

My car has 70.000km, regular maintenance done at the dealership.

the fuel pump, coils, injectors were replaced at 35.000km with index 7 ones. recent work was new spark plugs (gapped NGKs), and walnut blasted valves (thanks to a forum member here).

My car keeps getting the P0420 and P0430 codes, I can delet them, but they come back every week.
I have a OBD scanner and Torque, I have added few screenshots.

Do you have any insight on how to fix this issue? my car is stock a part for JB4 and intake.

KyleB

P0420 and P0430 are catalytic efficiency codes. They are basically telling you your catalytic converters are not operating efficiently enough, or at least that's what your oxygen sensors think

There are a total of four oxygen sensors in your car: two 'pre-catalyst' and two reference sensors behind the catalysts. The post cat-sensors are simply reference sensors (they do nothing to help adjust air/fuel ratios) and basically want to see clean exhaust gas coming out of the converters. If they don't, you get P0420 and P0430.

Sometimes you'll get these codes because your converters are truly not operating efficiently. Other times, it's the 02 sensors themselves that are faulty.

Is your exhaust system completely stock? Does the car feel like is driving OK? How long has the JB4 been on there?

Oxygen sensors aren't cheap, but if you think your converters aren't the problem and you keep getting faults on BOTH banks (1 and 2) you could try putting one new post-cat sensor in there and see if you're able to eliminate the fault code on at least one bank. If you are, then your problem is post-cat oxygen sensors. If you aren't, and your car is running OK, your converters may be fouled.

Good luck, be sure to update if/when you get this resolved.

Also, I'm going to use this as reason #33858234323 while I'll be going electric when the Tesla Model 3 comes out.

535t

thank you for your input Kyle,
the car had the JB4 for the past 20k km.
As you see from my screenshot the post cat O2 sensors are operating within the parameters so that leads me to believe that hey are fine. How can I check the health of my cats?
if the post O2 sensor are indeed the culprit, can an O2 simulator be used to fix my issue on the cheap and without impact to gas consumption and engine functions? We don't have mandatory emissions tests here.

pocholin

I had the exact same issue with my 2010 535i wagon @ 90k miles, plus a misfire code for cyl 6. Dealer replaced the same things you've done, except for the fuel pump. I had replaced my pre-cat o2s but still got the error codes. The final solution was when the dealer replaced all 4 o2 sensor, pre and post-cats. They told me that if that didn't solve it they were thinking of replacing the DME unit...and then the cats.
So, you might want to replace all 4 sensors and be done with it. Good luck.

535t

Thank you for the input.
I hope that this is not the case, 4 O2 sensors are expensive! Are they easy to reach without a lift?

pocholin

You can handle with a floor jack and stands. One of the pre-cat sensors needs to come out from the top, the rest from the bottom, much easier if you remove your passenger side tire and bottom covers.

535t

Can someone take a look at the attached log?
I suspect I have some missfire or leaky injector.

535t

I replaced all my injectors, as one on bank 2 was faulty.
I also put in new coils.

i still have the O2 sensors codes. before i go ahead and replace the sensors, is there a way to check if the cats are ok? are these the same for XI and 535i models?

pocholin

When my car had 85k miles, the dealer said it was very hard for the cats to go bad, they changed all 4 sensors and that fixed my problem. I don't know if there is a way to check the cats...but it is still cheaper the change the sensors than the cats. Changing 2 sensors didn't help, my problems ended when they changed all 4.