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'81 US spec GTV6. My EXH TEMP warning light comes on when I start the car, even though it's cold, and stays on. I gather it's meant to warn of an overheating catalytic converter. The only sensor I see screwed into the converter is the lambda sensor, and it doesn't look like there are enough wires coming out of it to send a temperature signal as well as control the fuel mixture.

Is there another sensor for temperature? And if it failed, would the light come on, i.e. fail safe? It's possible that a rodent has chewed through a wire, but not likely through the armored cable that I see coming off the lambda sensor.

Or ... I had a bad misfire, now fixed. Maybe some raw fuel got into the converter and damaged it, but would this trigger the warning light?
 

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1984 GTV6 (Maratona)
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On mine the wire to the sensor, which was removed long ago, shorted to ground (closed circuit) which energized the exhaust temp overheat warning light. I am not 100% sure the warning light is activated on open or closed. I should say mine appeared to light up when closed, but the wiring was buggered up. Someone else will hopefully know if the light is looking for an open or closed circuit.
 

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I think the light comes on when the probe sees the catalyst as hot. If it stays on for too long, a fuse on the board behind the glove box will pop, registering the catalyst as compromised. Once the fuse in blown the light will be permanently on.
 

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There is a thermocouple that screws into the cat. Usually has a braided mesh covering the wire, the lambda sensor is not usually braided. I will go take a picture of mine..

I think of mine as a mood ring. Comes on at different times depends on how its feeling..

Plenty of people just take out the light... just saying...
 

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I don't know if this helps since I have a 79 alfetta (not a GTV6), but my exhaust light is always on. I recently discovered this tied off sensor under the car. In other words, it seems my light is always on and not actually reporting any real information. When I posted about it here, suggestions included removing the light bulb or putting a piece of black electrical tape over the warning.
 

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I don't know if this helps since I have a 79 alfetta (not a GTV6), but my exhaust light is always on. I recently discovered this tied off sensor under the car. In other words, it seems my light is always on and not actually reporting any real information. When I posted about it here, suggestions included removing the light bulb or putting a piece of black electrical tape over the warning.
Forgot to add the image:
1672582
 

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I would assume if it wasn't reading real information since it wasn't inserted into the cat, it shouldn't have annunciated a warning further reinforcing the sensor was failed anyways, in my mind.
 

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Discussion Starter #8
I think the light comes on when the probe sees the catalyst as hot. If it stays on for too long, a fuse on the board behind the glove box will pop, registering the catalyst as compromised. Once the fuse in blown the light will be permanently on.
I didn't know there were any fuses there! Do you mean behind the glove box inside the cabin, or in the engine compartment in that area?
 

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There is a thermocouple that screws into the cat. Usually has a braided mesh covering the wire, the lambda sensor is not usually braided. I will go take a picture of mine..

I think of mine as a mood ring. Comes on at different times depends on how its feeling..

Plenty of people just take out the light... just saying...
OK, maybe it isn't the lambda sensor. It does have a braided mesh over the wire, so maybe it's the thermocouple.
 

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Discussion Starter #10
I think the light comes on when the probe sees the catalyst as hot. If it stays on for too long, a fuse on the board behind the glove box will pop, registering the catalyst as compromised. Once the fuse in blown the light will be permanently on.
Aha! I see you're in the UK. So your glove box is on the left, and presumably the fuse board is the same as mine, on the left.
 

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Aha! I see you're in the UK. So your glove box is on the left, and presumably the fuse board is the same as mine, on the left.
Shockingly, there was no requirement for cars in the UK to have a catalytic converter until 1990. I just recall the set-up from the USA spec GTV6 I had in 1994, the light was on, and the fuse was blown when I got it.
 

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1979 Alfa Romeo Sprint Veloce
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I recommend deleting the system altogether, mine recently exploded on me and i was able to fix and repair the damage. luckily my car didn't burn down! here's my post with more info, but in short the white block on the passenger side dashboard area is prone to literally exploding white smoke once it goes and in mine, i also noticed the wiring that's wrapped in fabric for the warning light itself can get grounded to the car and seemed that was another cause of the system to short and possibly burn down a car lol
 

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I suppose if your car is running very lean you could overheat the cat and in which case that light might be actually telling you something. But, more than likely it is grounding out due to some other wiring issue and telling you erroneous info. Shoot an infrared temp gun at the cat and see it's temperature. In 2021 given that you are probably running 93 octane and assuming your ignition timing is set to factory spec or close to i don't think the cat is actually overheating. I have an 82 and to be honest the plug going that light was disconnected. I plugged it in one day and it shined brightly. I disconnected it, the car runs perfect. It was an emissions requirement back in 1982. At this point throw that out out the window and just tune the engine to not run hot. My $.02. Had no idea the box can smoke out but i have the light disconnected and it's been 7 seasons of driving without an issue.
 

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I suppose if your car is running very lean you could overheat the cat and in which case that light might be actually telling you something. But, more than likely it is grounding out due to some other wiring issue and telling you erroneous info. Shoot an infrared temp gun at the cat and see it's temperature. In 2021 given that you are probably running 93 octane and assuming your ignition timing is set to factory spec or close to i don't think the cat is actually overheating.
I'm not sure of the exact temperature range of the GTV6 EGT sensor, but based on experience with other systems, the only things that will cause the light to come on as intended are high EGTs from a misfire, or extremely retarded ignition timing (during normal running, peak EGTs occur at the stoichiometric air/fuel ratio of 14.7:1).

In other words, you would likely know if your engine is running badly enough to cause the system to function as designed. If it is running decently well, then you might consider disabling the system as others have suggested.
 
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