I'm assuming that the heat was working fine until the CEL light came on so it is a safe assumtion that the two are related. Get the code and report back to the forum, also check your coolent level and make sure it is where it is supose to be.
I think Willie's correct. fwiw: earlier this year I apparently lost a few cups of coolant when doing a repair,, the temp gauge in the car indicated nothing, but the OBDIICC gauge showed my temp spiking radically [steam] then dropping to a bit higher than normal, [95C vs. normal 91C-92C] and the MIL appeared right at the same time.
is on youtube.
Highwater's posted on IC a great diagram of the first gen's coolant system and it is mirrored here if you want to check for leaks.
If you think it's an internal leak, ie. blown head gasket, you can note this in the purge watching for bubbles arising that may vary with rpm; or after the car's warmed up, holding a kleenex over the exhaust and watching the tissue disintegrate with all the excess water vapor. Also uf far gone, white smoke in exhaust. I hope it isn't that bad.
fwiw: Never check rad fluid or top up via the rad cap as it's lower than the highest point of the coolant system.
The mark on the coolant overflow bottle is on the same level as the top of the radiator fill neck. Therefore no coolant is lost when radiator cap is removed (WITH ENGINE COLD). As for me, anytime I find my coolant overflow bottle empty I will fill overflow bottle AND radiator (after engine cools). I would be concerned that air in the top of the radiator would prevent the overflow bottle from functioning as designed.
The overflow bottle could be below the radiator level as it is a pressure thing not effected by gravity. And a "siphon" action as the radiator cools.
On my FIT, it is real hard to see the levels on the overflow bottle due to it's location.
The overflow bottle fill cap is about 5 in. below the level of the radiador cap.
01 MT "Little Red Rocket"
The first "TURBOCHARGED" Hybrid, Insight G1- (01/2003)
MaxIMA Battery (Serial #2), on 8/25/12 @ 301,520 miles
Use: 320,000 mi. @ 57.8 LMPG
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