[segmentationfault]

Hello people, new member here. So I've had CTS catted downpipe and BM3 OTS stage 2 91 on my 2018 440ix GC for about 5 months. The car has 58k miles now and I've had so much fun especially in the Canadian winter now with snow tires on.

However, recently I got two consistent codes and CEL as following (car still drives fine):

128101: Oxygen Sensor 1 Bank 1 System Check: Signal Stuck on Lean

118601: Lambdasonde 1 bank 1, fine mixture control: exhaust gas too rich

I remember having these codes about 2 weeks after the install but thought it's just censors calibration and cleared it. I haven't got them since then, but now they are reappearing shortly after I clear it so I took it to the shop.

The diagnosis was that there's a leak caused by the missing welding spots on the upstream O2 sensor bung as shown in the attached photo, where you can also see soot coming out. They were able to confirm there is exhaust gas coming out of that area, which also explains why I sometimes got the smell in the cabin.

The shop recommends replacing downpipe or fixing the weld but either way the pipe needs to come out. I contacted CTS for warranty but they only issue replacement/repair after the item is sent back and reviewed. Which means I have to swap back to stock, wait for replacement, then install again (and hope it will work this time)! That's two extra installation cost and shipping

So now I'm seriously considering just getting a quality downpipe like ER or AA and be done with it. And sell the CTS replacement if I ever got it. But what do you guys think? Have you seen welding on the downpipe like this (not covering all around the bung)? Any input will be much appreciated!

[n55david]

Originally Posted by segmentationfault

Hello people, new member here. So I've had CTS catted downpipe and BM3 OTS stage 2 91 on my 2018 440ix GC for about 5 months. The car has 58k miles now and I've had so much fun especially in the Canadian winter now with snow tires on.

However, recently I got two consistent codes and CEL as following (car still drives fine):

128101: Oxygen Sensor 1 Bank 1 System Check: Signal Stuck on Lean

118601: Lambdasonde 1 bank 1, fine mixture control: exhaust gas too rich

I remember having these codes about 2 weeks after the install but thought it's just censors calibration and cleared it. I haven't got them since then, but now they are reappearing shortly after I clear it so I took it to the shop.

The diagnosis was that there's a leak caused by the missing welding spots on the upstream O2 sensor bung as shown in the attached photo, where you can also see soot coming out. They were able to confirm there is exhaust gas coming out of that area, which also explains why I sometimes got the smell in the cabin.

The shop recommends replacing downpipe or fixing the weld but either way the pipe needs to come out. I contacted CTS for warranty but they only issue replacement/repair after the item is sent back and reviewed. Which means I have to swap back to stock, wait for replacement, then install again (and hope it will work this time)! That's two extra installation cost and shipping

So now I'm seriously considering just getting a quality downpipe like ER or AA and be done with it. And sell the CTS replacement if I ever got it. But what do you guys think? [...]

Offer to buy one ahead if time while you wait for the old one to be inspected.. they will just refund you after checking it out.

[segmentationfault]

Originally Posted by n55david

Offer to buy one ahead if time while you wait for the old one to be inspected.. they will just refund you after checking it out.

Thank you for the advice! However CTS told me their warranty doesn't work this way and ONLY replacemnt/repair will be issued after inspection. Honestly does not sound customer friendly at all.

Fortunately I found a shop that is willing to install a new one for me before the replacement comes. They will take the replacement and refund me the part. I'm inclined to go this route.

Will update once I get warranty reviewed by CTS. If it's indeed welding defect, that's some big QC failure

[mike@x-ph.com]

Im sorry to hear that OP, it's unusual for a manufacturer to refuse to sell a new one until the warranty check is complete.