Faulty Cat causing engine problem? - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

Enrique_13 · 06-28-2018, 07:35 PM

Hey guys I’ve had a faulty catalytic converter for about two months now, it’s the front one by the header, as described by my mechanic. After this finding, sometimes when I drive ( usually when I’m pushing my engine a bit more into 3000 rpms and higher, the rpms indicator starts rapidly going down and up. Almost like my car is in limp mode. To fix this issue, i usually pull over to the side and rev my car a couple times into at least 6000rpms and drive again. I’m not sure why this happens but it can be stressful as I have to drive slowly in order to avoid this problem happening to my rpms. I am about to purchase a new catted header so hopefully this helps. Has this happened to anyone before?

Clipdat · 06-28-2018, 07:43 PM

How did your mechanic make the determination that the primary cat was "faulty"?

Enrique_13 · 06-28-2018, 07:50 PM

Sorry I forgot to specify a couple things. The first code that appeared was P0420 CATALYST SYSTEM EFFICENCY BELOW THRESHOLD (BANL 1). I have been getting a horrible 18mpg. However after a few weeks the problem above occurred and i got an ABS light, a traction control light, and a blinking check engine light. My next check I got these codes

C1201 Engine Control System Fault
C1294
U0073 Control Module Communication Bus Off
U0126 Lost Communication With Steering Angle Sensor Monitor

FRSBRZGT86FAN · 06-28-2018, 08:03 PM

Quote:

Originally Posted by Enrique_13

Sorry I forgot to specify a couple things. The first code that appeared was P0420 CATALYST SYSTEM EFFICENCY BELOW THRESHOLD (BANL 1). I have been getting a horrible 18mpg. However after a few weeks the problem above occurred and i got an ABS light, a traction control light, and a blinking check engine light. My next check I got these codes

C1201 Engine Control System Fault
C1294
U0073 Control Module Communication Bus Off
U0126 Lost Communication With Steering Angle Sensor Monitor

U0073 and U0126 appears sometimes when someone plugs in something odd or faulty into the OBDII port. How many miles do you have? It's odd for a CAT to go bad 5 years in, did you have issues with burning oil or anything else like that? I would make sure you take it to a dealer that knows this car a bit better.

Did he Check the o2 sensors specifically?

Grady · 06-28-2018, 08:06 PM

Plugged cat????, cheaper to gut that bitch and buy a tune!

Enrique_13 · 06-28-2018, 08:09 PM

Quote:

Originally Posted by FRSBRZGT86FAN

U0073 and U0126 appears sometimes when someone plugs in something odd or faulty into the OBDII port. How many miles do you have? It's odd for a CAT to go bad 5 years in, did you have issues with burning oil or anything else like that? I would make sure you take it to a dealer that knows this car a bit better.

Did he Check the o2 sensors specifically?

It has about 108,000 miles. I don’t believe so, but I figured since I wanted to get a new header anyway I would purchase it. And no issues with oil.

humfrz · 06-28-2018, 08:39 PM

Quote:

Originally Posted by Grady

Plugged cat????, cheaper to gut that bitch and buy a tune!

DANG, Grady, you're big on gutting cats this week …

I'll betcha beck in the day, you were big on burning out glass packed mufflers ..??

humfrz

Enrique_13 · 06-29-2018, 01:19 AM

I tried recording it happening , see what y’all think

Grady · 06-29-2018, 09:56 AM

Quote:

Originally Posted by humfrz

DANG, Grady, you're big on gutting cats this week …

I'll betcha beck in the day, you were big on burning out glass packed mufflers ..??

humfrz

Never burned them out but did have them on my 73 bronco with a 351 Windsor.

Razorlor · 06-29-2018, 11:08 AM

Flashin CEL indicates a misfire, which poor exhaust flow can cause. Clogged cat doesn't sound out of the question.

If this happens at lower speeds as well. You could remove the upstream 02 and see if this problem goes away (creating a new path around the restriction).

06-28-2018, 07:35 PM	#1
Enrique_13 Member Join Date: Apr 2018 Drives: 2013 Subaru BRZ Location: Tx Posts: 23 Thanks: 1 Thanked 1 Time in 1 Post Mentioned: 0 Post(s) Tagged: 0 Thread(s)	Faulty Cat causing engine problem? Hey guys I’ve had a faulty catalytic converter for about two months now, it’s the front one by the header, as described by my mechanic. After this finding, sometimes when I drive ( usually when I’m pushing my engine a bit more into 3000 rpms and higher, the rpms indicator starts rapidly going down and up. Almost like my car is in limp mode. To fix this issue, i usually pull over to the side and rev my car a couple times into at least 6000rpms and drive again. I’m not sure why this happens but it can be stressful as I have to drive slowly in order to avoid this problem happening to my rpms. I am about to purchase a new catted header so hopefully this helps. Has this happened to anyone before?

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06-28-2018, 07:50 PM	#3
Enrique_13 Member Join Date: Apr 2018 Drives: 2013 Subaru BRZ Location: Tx Posts: 23 Thanks: 1 Thanked 1 Time in 1 Post Mentioned: 0 Post(s) Tagged: 0 Thread(s)	Sorry I forgot to specify a couple things. The first code that appeared was P0420 CATALYST SYSTEM EFFICENCY BELOW THRESHOLD (BANL 1). I have been getting a horrible 18mpg. However after a few weeks the problem above occurred and i got an ABS light, a traction control light, and a blinking check engine light. My next check I got these codes C1201 Engine Control System Fault C1294 U0073 Control Module Communication Bus Off U0126 Lost Communication With Steering Angle Sensor Monitor

06-29-2018, 01:19 AM	#8
Enrique_13 Member Join Date: Apr 2018 Drives: 2013 Subaru BRZ Location: Tx Posts: 23 Thanks: 1 Thanked 1 Time in 1 Post Mentioned: 0 Post(s) Tagged: 0 Thread(s)	I tried recording it happening , see what y’all think

06-29-2018, 11:08 AM	#10
Razorlor Member Join Date: Dec 2017 Drives: 2017 BRZ Limited, Perf Package Location: STL Posts: 50 Thanks: 5 Thanked 13 Times in 8 Posts Mentioned: 1 Post(s) Tagged: 0 Thread(s)	Flashin CEL indicates a misfire, which poor exhaust flow can cause. Clogged cat doesn't sound out of the question. If this happens at lower speeds as well. You could remove the upstream 02 and see if this problem goes away (creating a new path around the restriction).

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