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What is the cause of DTC 15

NVW, yes got it I have the list and actually used GMTDScan Tech to read and clear the codes but what I'm looking for is the cause of the code. IE what causes a DTC 15 - Engine Coolant Temperature (ECT) Sensor Circuit High (Low Temp)? My ECT reads and acts normal as far as I can tell.
 
It may be the sensor in the crossover, are your glow cycles still the same length of time?

Somewhere on here is a chart that gives the ohms resistance for any given temp.
 
What temps are you seeing on the scanner, and for how long. I believe you have a 14 minute window to get over 170 degrees, if it doesn't it will code.
 
NVW, thanks for the link.

THEFERMANATOR, you learned me something! Never heard of that before. I'll have to check it out.

How do I ohm out the the ECT sensor? Put my multimeter leads on the ECT sensor and block?

I've never seen a sensor on my coolant crossover tube but I'll check again. I know that there is an ECT sensor on the block close to the driver side front
 
There are two sensors. a 1 wire, and a 2 wire. you are looking for the one with 2 wires. check crossover first, then front of driver head and rear of passenger head. If you have a scanner, drop a thermostat is the radiator and watch the scanner temps, then fire up the engine. If the numbers match it's good.

Otherwise if you pull the sensor out, put it in a pan of water on the stove with an ohm meter on it, and a thermostat in the water to compare against the chart mentioned above.

What thermostat(s) do you have in it btw?
 
What Ferm said. The engine has to get to a minimum temp I thought it was 160F in 10 minutes but my memory is bad.

Once I had a thermostat get stuck open a bit and it would not warm up fast enough. I put new thermostats in and never saw the code again.
 
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