Topgear 200 cell x-cats and check engine light (Carrera 4)

My 2002 C4 has had TopGear 200 cell X-pipe sports cats for nearly two years now. I seem to get very occasional appearances from the check engine light that, according to my basic code reader, come back as a combination of one or two (never all) of the following: 1. N/A 2. P0156 O2 sensor circuit malfunction (bank 2 sensor 2) 3. P0139 O2 sensor CKT slow response (bank 1 sensor 2) 4. P0136 P O2 sensor circuit malfunction (bank 1 sensor 2) Is it possible this is because of the sports cats (there are only warnings on Topgear's site for the 100 cell cats) or simply coincidence and 18 year old sensors starting to go bad having been disturbed. It's something I'd like to sort despite not noticing any change in performance but I'm unsure whether replace the O2 sensors (sensor 2 is downstream of the cats I assume?) would do the job or whether it's actually something I could get mapped out? I'd been considering getting the car to Chipwizards anyway but clearly don't want to present something not working.

I've the same xpipe cats on my C4 though had to change the cat sensors for my install as the old ones wouldn't come out of the original ones. With the new sensors (mine just have a pair as it's an early car) mine hasn't shown any EML warnings so I can only suggest it could be the age of the cat sensors. Hopefully Demort will be along shortly.....

I had new sensors when I had mine put on and not had the problem. How've we, You may also want to check the X seams .

Hopefully a pair of new sensors then. Although... what issue have you found with the X-pipe itself? Splitting at the seams?

Almost every occasion i've ever had to handle an issue like this, its down to the sensors but people blame the cats. Poor cats are usually the victims. I can count on one hand the number of times an investigation has actually proven any fault with the catalytic converters themselves (on two fingers, to be specific). In fairness, I think people's sensors are usually more forgiving of the OEM 400 Cell cats whereas switching out the cats can expose sensor issues that were slipping under the radar before.

Double post please remove.

I have a 2002 C4 with TopGear 200 cell X-pipe sports cats and I also get an occasional EML: P2098 Post Catalyst Fuel Trim System Too Lean Bank 2 P0156 O2 Sensor Circuit Bank 2 Sensor 2 RPM Technik tested the sensors and they were fine (they had only been replaced a couple of years prior) and concluded it was because the cats were aftermarket.

Must be a 2002 Lapis blue C4 thing :mrgreen: Thanks. The issue is so occasional I was minded to think it was the sensor(s) and possibly that 200 cell cats are on the edge of what the car thinks is ok. I'll get it looked at in September when I get the car serviced. They can visually inspect the cat pipes, swap the sensors and go from there. If on new sensors I continue to get the occasional issue and there are no issues that can seen from the outside with the cats I'll see whether it's something a remap can work around.

I have top gear 200cel cats on my 2002 C4S and also occasionally get the engine warning light coming on, all I do is plug in my code reader and delete the light.It doesn't bother me as I put it down to aftermarket cats.Other than that ir runs. really well on these cats

Hi guys, I'm replacing mine in the morning, I've got the bumper off etc. When I remove the old cats would you unplug the sensor clip and leave it in the cat, or unscrew the 22mm bolt while it's on the car, then screw straight back in? Can't decide which is best practice 🤔

I removed the air box. Unplugged the O2 sensors and tried to remove when I had them off the car. I would imagine it would be a bit of a pig to remove old sensors in the car, mainly due to room and seized in place. If your trying to remove the old sensors, good luck. I had to buy new ones unfortunately.

I have plenty of room as I've removed the bumper and heat shields, I have sprayed them in antiseize, but not yet tried to remove... mine is a 2003 so has 4 sensors. Just in case where did you get the new sensors from?

I purchased all 4 for £150 from Auto doc. However I have a 997.1 and I know the ones on yours might be slightly different? You might have a black plug with 4 pins? I think? Where as the later ones are slightly different shaped plugs. Once you know what type you have it might be worth dropping Matt997 a pm as he managed to buy some quite cheap I believe? Possibly the same as yours. When I tried to remove mine they were quite rusty. As soon as I tried to remove the O2 sensor the nut just rounded. I tried using the proper O2 socket and heat, both no good. It appears to me as being luck of the draw. Some seem to come out quite easy, others not so.

Cheers pal, visually they looked OK this afternoon, as do the cat/exhaust bolts, (new engine 2k ago) I bare that in mind if u can't get them out 👍

I've got a brand new set of sensors (the rear set) for a 996 as I thought I'd need 4 sensors, but only actually needed 2 - mine are unused/still in the box that I need to sell if you PM me. The front/rear sensors are I think the same part number btw.