Calling all Electronic Wizards

[Amorphous]

Short Story: Where does the coolant sensor get its power from? And if it comes from the ECU, does the ECU need another input or trigger from another sensor before it supplies power to the Coolant Sensor?

Long Story: I just bought a 90 Eclipse Turbo and it failed my state’s emission test. I checked the O2 sensor and got zilch off Pin 2 at any RPM range. I understand the turbos use a four wire heated sensor that operates in the 600 deg F range. Even after the car warms up…no voltage, with no check engine light. I went and checked the coolant sensor to see if it had believed the car was warmed up but I found no 4.5 – 4.9 volts on the harness. I’m replacing the O2 Sensor…can anyone help with where this coolant sensor gets its power from?

 

[92redman]

What code was in there? Power and ground for the coolant sensor comes from the ECM. The ground(G/B wire) is shared between the tps, egr temp sensor(for cal.), and MAF. The 5v supply for ECT is a yellow/green wire that connects to pin 20 at the ECM, if you don't have 5v at the sensor, you should check to make sure there is 5v leaving the ECM(when looking at the connector with the locking tab up, it should be 5th pin from the right on the bottom row of the largest ECM connector), if it's good you have an open or high resistance in the wire.