Today was a rather hot day and i was driving around doing errands when on my dash by the idiot-lights i noticed one of them lit up reading "HEAT" and depicted a little box or such with open ends....

what the hell is that!?

i drive an S5 turbo....

 

your cat converter was overheating.

Your car is probably running rich

 

It normally means the cat is overheating due to a fuel or ignition problem, but since I doubt you have a cat, it means you have an issue with the wires for the temp sensor that was in the stock cat. When I removed my cat I had to put a jumper wire across the sensor's plug to mimic the switch in a cold state and keep the warning light off.

And before anyone says anything, yes the JDM cars did have an exhaust temp sensor in the cat, as opposed to the floor temp sensor US models have.

 

yeah it's off now and has stayed off all day....

akward....

and yeah, no cats for me....

:P

 

Check out the wiring for the temp switch. It might be hanging under the car or it might have been pushed back up through the hole in the floor. It's right under the left seat.

 

if the cats is overheating, wouldn't that mean your running lean? The richer the AFR the less hot the exhaust is.

 

No, because the way a cat works is to oxidize the unburnt Hydrocarbons.

So more Hydrocarbons, hotter the cat gets, trying to oxidize them.

 

Unburnt fuel in the exhaust will sent the cat temp upwards and turn the warning light on.