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Discussion Starter #1
I've got a 91 US model and I recently started getting a flickering check engine light. I pulled the code, 1223, coolant temperature sensor. I also get an occasional moment where the water temp gauge drops to zero, then returns on its own. Given the random flickering of the CEL, I figured it might just be the connect. I check both temp sensors near the thermostat and both connections seemed clean and secure. Which one of these sensors triggers the CEL? The blue connector or the black connector? What is the failure mode of the sensor, would it give this flickering behavior?

Thanks.
 

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Discussion Starter #2
Well the issue went away. I'm pretty sure it was related to the connections. I did some light engine bay cleaning (no hose or pressure sprayer) and I think some moisture worked its way into a connection. Live and learn.
 

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Discussion Starter #4
An update:

I started getting the flickering CEL again yesterday, same code: 1223. I looked at realoem and saw two different part numbers for the two coolant sensors. They look identical to me (although both are pretty dirty) so I ordered one of each part number. I'm going to replace both and see if my troubles go away.
 

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Discussion Starter #5
Fixed it. One of the sensor I got (for the thermostat housing) didn't fit due to a wrong thread size. Luckily the other one, for the water pipe, did and fixed the issue. This is the sensor, for reference. It did have a matching blue connector. Got to put 300 miles on the car in a country romp this weekend!
 

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I am looking to replace my coolant temp sensor as well (it "floated between blue and 1/2 mark during freeway driving, but ok in city driving) - so which one fixed your issue? I was not aware that there are two different coolant temp sensors to be replaced (t-stat housing AND water pipe)?
If you have any pics to show which one(s) you replaced, that would be greatly appreciated and helpful.
Thanks.
 

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Discussion Starter #7
If you look here, it's #13 if I recall correctly. It's the one furthest back, near the exhaust manifold. It fixed the CEL. I did not replace the one closest to the thermostat.
 

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I think I have this issue. I was driving yesterday and the coolant temp suddenly hit the floor. After a brief heart attack (worried that the engine had dumped coolant and cooked) I realised that coolant was circulating as normal. I know the blue sensor feeds the ECU (and is probably a good one to renew anyway) but I dont know for sure which one feeds the gauge. if anyone knows whether that is the blue one or the black one (nearer the thermostat) I'd be very grateful.
 
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