Testing the Temperature Sensor

[RallyEclipse98]

I recently removed my coolant temp. sensor from my thermostat housing when I took off the head to address the head gasket. I broke the wire leading to the sensor but put on a new connector. The dash needle doesn't read anything. I used a tester and put the positive needle on the sensor and negative needle on the thermostat housing where it grounds. I had juice. So this means I'm getting power to the sensor? I guess I have a faulty sensor? After the head gasket change I re-installed the factory sensor. I just find it weird the sensor went bad at the same time I broke the wire...

Thanks for any and all help!!!

 

[DSM1G90]

You popped the temp sending unit, not the sensor itself (temp sensor are attached to the ECU to aid in proper air/fuel mixture). Get a new sending unit.

Sending units are just a therm resistor that changes value due to sensing heat, and the the resistor is changing resistance value between the positive and negative leads to the coil attached to the gauge needle.

If you touch the positive lead direct to ground with key on, the needle should rise to hot real quick.

 

[luv2rallye]

The 1 wire ECT sensor runs the dash temp gauge. Unplug and attach a ground to the harness side sensor wire. Turn key to ON. Temp gauge should slowly go to maximum. If not the wiring or gauge is bad. Check resistance of the sensor itself to ground. Should be 104 (+/-13.5) ohms when coolant is 158*F. Value increases when temp decreases (ie. at temp lower than 158* value is more than 104 ohms).

 

[RallyEclipse98]

The 1 wire ECT sensor runs the dash temp gauge. Unplug and attach a ground to the harness side sensor wire. Turn key to ON. Temp gauge should slowly go to maximum. If not the wiring or gauge is bad. Check resistance of the sensor itself to ground. Should be 104 (+/-13.5) ohms when coolant is 158*F. Value increases when temp decreases (ie. at temp lower than 158* value is more than 104 ohms).

So I can unplug the connector to the sending unit, shove a nail into the connector and ground it to the thermostat housing (basically bypassing the sending unit) and if my needle doesn't rise on the dash, I either have bad wiring or a bad gauge? Since I have power to the sending unit (my previous test), I must have a bad gauge?

 

[DSM1G90]

Yeppers, as Luv2 mentions .. plain and simple.