CO metering at exhaust, Prius 2012

I want to anecdotally check with those who got experience with CO readings if these values are fairly "normal".

I'm using a toptes CT 580.I wamed the car for a while, until it got warm inside, the air temp was around -8C.

When I began reading, I was surprised to get values between 10-30ppm, regardless if I was a few inches away or at tailpipe. Eventually, I got some 50-120ppm readings as the engine went through a few cycles of ICE engine going on/off.





Then I caught it, right as a new ICE engine cycle was starting and I got an initial 450ish ppm reading that tapered off to those familiar values above.



I didn't know what to expect. I deduct that combustion is poor as the engine restarts and then quickly becomes more efficient.

I've been burning some maple toothpicks, for reference, and I got around 200ppm sharply dropping to 50ppm then tapering to 0-10ppm.

 

I bought it to calibrate AFR on a diesel heater. I was suspecting that I had a leak up front and I wanted to check that.

As far as I understand any burn - be it fire or engine burning a fuel - has CO as a byproduct and a CO meter would tell you basically if that burn is efficient. So I'm not sure there is such a thing as a CO meter just for exhausts. Basically it reads the CO concentration in the air at that point. If it can withstand the temperature, then it's good. That model is waterproof according to the specs so it can withstand the vapors.

Got word from a youtuber who is a mechanic and reviews diesel heaters and whatnot. He got ultra performant CO/gas meters as well as cheaper ones like this one. According to him the numbers look ok. As the catalytic converter warms up, the CO gets converted - hence the drop in CO.