2004 Chevy Blazer - How to tell if ECT Sensor is bad?
 

So I recently had my check engine light come on, and upon using the reader, I received code P0128

I topped up the coolant level, but I'm not sure how to tell if the sensor itself is bad, so I'm wondering if anyone here knows?

I can't recall if the ECT sensor is also for the gauge, I think it is. If it is, and you dont have a scan tool that can do live data, then you can short the two pins out in the wiring harness after unplugging it. If your gauge needle goes to full hot, then likely its good.

The real method is to get a scanner with live data, and look at the ECT reading on there.

there should be 2 sensors. One at the intake manifolds for the computer. the one on the side of the block is for the gauge. replace the manifold one and see what happens. they are about 15 bucks. try to get the one with red sealant already applied. makes things simple.

Thanks for the info guys, I gotta get this fixed ASAP due to upcoming necessary e-testing.

nothing to it. deep well socket...take it out,screw new one in,done.

2004 only has one sensor. The PCM uses the data for engine controls and the data is shared with the BCM which controls the dash temp gauge. DON'T short the wires, unless you want a new PCM ;)

99% of the time P0128, (Coolant temperature below thermostat regulating temperature) means the thermostat is stuck open and needs to be replaced. The link in post #1 hits the nail on the head.