Heating catalyst without starting engine? - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

BRZyJ · 08-21-2017, 10:29 PM

I had this happen the other day but I can't replicate it. I had my head unit out and was messing around with some Torque gauges after I put it back and I noticed the cat in the front pipe was warming up, pretty quickly. I let it get to ~450° and started the engine, nice and (fairly) quiet.
I figured I'd stumbled on a way to avoid the loud cold start without messing with the tune, but it won't do it again.

Was it just a weird fluke or did I do some sequence of things I can't remember? The temperature started going up as soon as ACC was on, I don't remember doing anything out of the ordinary before that.

Ernest72 · 08-22-2017, 07:18 PM

Cat is warmed up by exhaust gases, so if car is not running what is heating it?

mav1178 · 08-22-2017, 08:03 PM

How can the front cat temp be detected if there's no thermoprobe?

BRZyJ · 08-22-2017, 08:48 PM

Quote:

Originally Posted by Ernest72

Cat is warmed up by exhaust gases, so if car is not running what is heating it?

I dunno...a google search yields a bunch of results for electrically heated catalysts so I guess such a thing exists...never heard of it myself.

Quote:

Originally Posted by mav1178

How can the front cat temp be detected if there's no thermoprobe?

Dunno that either...just happened to see that PID as I was messing around

.

Turdinator · 08-22-2017, 10:51 PM

I remember reading somewhere on the forum that there is a calculation the ECU does to approximate cat temps. There may be a way you fooled the calculation...

humfrz · 08-23-2017, 12:32 AM

I don't know how that happened ....... but, I sure hope it doesn't happen again and burn your car up ......

humfrz

BRZyJ · 08-23-2017, 01:34 AM

Quote:

Originally Posted by Turdinator

I remember reading somewhere on the forum that there is a calculation the ECU does to approximate cat temps. There may be a way you fooled the calculation...

Thx...I dug around and did find that mentioned a couple of times. Tried to get it to do it again a few times this evening, but nope. :/

Quote:

Originally Posted by humfrz

I don't know how that happened ....... but, I sure hope it doesn't happen again and burn your car up ......

:O lol... now I kinda wish I'd let it keep going before starting it to see if it went past the normal range, which seems be mid 800s°F. I'll either forget about it or waste a ton of time trying to reproduce it...meh...

guybo · 08-23-2017, 06:07 AM

There's an oxygen sensor heater. Look up all the P0031 CEL's that have posts on this forum. I think the ignition was in the on position instead of ACC and that allowed the O2 sensor to heat itself up to temp. You're really stressing your battery though, not good.

steve99 · 08-23-2017, 06:52 AM

The 02 sensor in these cars has a heater circuit to regulate temp of sensor.

Buy measuring the current in the heater circuit the ecu can approximate the exhaust/cat temps
the ecu regulates the temp of the 02 sensor

You can read the parameter via Techstream or OBD software like Torque.

http://www.romraider.com/forum/viewt...t=8134&start=0

BRZyJ · 08-23-2017, 02:42 PM

Quote:

Originally Posted by guybo

There's an oxygen sensor heater. Look up all the P0031 CEL's that have posts on this forum. I think the ignition was in the on position instead of ACC and that allowed the O2 sensor to heat itself up to temp. You're really stressing your battery though, not good.

Huh...so the O2 sensor heater had to be heating the cat. You are correct, it was ON not ACC, my mistake. After reconnecting the head unit I messed with some Torque displays with ACC on, then switched to ON which is when the temperature immediately began climbing. Hasn't done it since...weird. Battery is probably due to be replaced soon either way...still on the original.

Quote:

Originally Posted by steve99

The 02 sensor in these cars has a heater circuit to regulate temp of sensor.
Buy measuring the current in the heater circuit the ecu can approximate the exhaust/cat temps
the ecu regulates the temp of the 02 sensor

I see...I saw in the other threads that PID was a calculated value, but not where it came from, thx. Well, hopefully it's not a symptom of an impending failure.

08-21-2017, 10:29 PM	#1
BRZyJ Senior Member Join Date: Aug 2016 Drives: 2013 BRZ Limited / 2024 G70 3.3T Location: Vegas Posts: 270 Thanks: 249 Thanked 174 Times in 110 Posts Mentioned: 4 Post(s)	Heating catalyst without starting engine? I had this happen the other day but I can't replicate it. I had my head unit out and was messing around with some Torque gauges after I put it back and I noticed the cat in the front pipe was warming up, pretty quickly. I let it get to ~450° and started the engine, nice and (fairly) quiet. I figured I'd stumbled on a way to avoid the loud cold start without messing with the tune, but it won't do it again. Was it just a weird fluke or did I do some sequence of things I can't remember? The temperature started going up as soon as ACC was on, I don't remember doing anything out of the ordinary before that.

08-22-2017, 10:51 PM	#5
Turdinator Señor Member Join Date: Aug 2012 Drives: 86 GT/'74 TA22 Celica/Kangaroo Location: Melbourne, Australia Posts: 1,706 Thanks: 1,107 Thanked 769 Times in 480 Posts Mentioned: 13 Post(s)	I remember reading somewhere on the forum that there is a calculation the ECU does to approximate cat temps. There may be a way you fooled the calculation... __________________ 1974 TA22 Celica 2013 86 GT

08-23-2017, 06:52 AM	#9
steve99 Banned Join Date: Dec 2013 Drives: FT86 Location: Australia Posts: 7,996 Thanks: 1,035 Thanked 4,998 Times in 2,985 Posts Mentioned: 598 Post(s)	The 02 sensor in these cars has a heater circuit to regulate temp of sensor. Buy measuring the current in the heater circuit the ecu can approximate the exhaust/cat temps the ecu regulates the temp of the 02 sensor You can read the parameter via Techstream or OBD software like Torque. http://www.romraider.com/forum/viewt...t=8134&start=0 Last edited by steve99; 08-23-2017 at 07:03 AM.

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08-22-2017, 07:18 PM	#2
Ernest72 Senior Member Join Date: Jul 2016 Drives: 16 Silver BRZ, 04 Silver WRX wagon Location: Rockland county, NY Posts: 1,431 Thanks: 186 Thanked 776 Times in 446 Posts Mentioned: 1 Post(s)	Cat is warmed up by exhaust gases, so if car is not running what is heating it?

08-22-2017, 08:03 PM	#3
mav1178 Senior Member Join Date: Apr 2013 Drives: 2005 Toyota Camry Location: 91745 Posts: 6,562 Thanks: 493 Thanked 6,099 Times in 3,030 Posts Mentioned: 95 Post(s)	How can the front cat temp be detected if there's no thermoprobe?

08-23-2017, 12:32 AM	#6
humfrz Senior Member Join Date: May 2013 Drives: 2013 FR-S, white, MT Location: Puyallup, WA Posts: 30,436 Thanks: 29,833 Thanked 32,866 Times in 16,849 Posts Mentioned: 717 Post(s)	I don't know how that happened ....... but, I sure hope it doesn't happen again and burn your car up ...... humfrz

08-23-2017, 06:07 AM	#8
guybo Huge E85 fan! Join Date: May 2016 Drives: 2016 Scion FRS Location: Tampa, FL, USA Posts: 1,850 Thanks: 539 Thanked 1,010 Times in 605 Posts Mentioned: 32 Post(s)	There's an oxygen sensor heater. Look up all the P0031 CEL's that have posts on this forum. I think the ignition was in the on position instead of ACC and that allowed the O2 sensor to heat itself up to temp. You're really stressing your battery though, not good.

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