Heating catalyst without starting engine?

[BRZyJ]

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]

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

[mav1178]

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

[BRZyJ]

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.

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]

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]

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


humfrz

[BRZyJ]

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. :/

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]

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]

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]

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.

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.