After engine overheated due to hole in a radiator hose, I had an engine diagnostic for the Temperature sensor bad.

I replaced the sensor, and tested the old one, and did not see that it was bad.

After replacement the diagnostic would not reset, and still showed a bad temp. sensor.

I pulled the wire connector and put a meter across the two wire connectors. With the engine off and ignition switched on I was getting 325 millivolts. When the engine started the voltage reversed, and I was getting 4.25 volts from the ECU.

I am not sure what the bad temperature sensor is doing to my fuel economy? but want to get the engine light off?

Anyone know what the ECU does when it thinks the sensor is bad.

I could also hook up the spare temp sensor and check DC current.

Any suggestions?

Thanks - Oldguy

The sensor your after should read resistance change as temperatures go up. It puts out less resistance the hotter it gets. Couple 2.5 thousand ohms @ 68 degrees to about 350 to 400 ohms hot, at 176 degrees as I remember.

You probably found the instrument gauge sender.

The ECU does not output anything to the sensor.

A bad wire or connector back to the ECU would also keep the light on.

Computers don't lie considering all the thing they take care of.

They may some day.

Then tell you its time for a new car and how far to the nearest dealer!

Part of that is true...Whoa! Next thing they will think of, taxing medical benefits?...?

Which Temperature Sensor did you replace? There is the block temperature sending unit and, under the third intake runner, an Engine Coolant Sensor. The last is the one that the ECU reads to determine the fuel mix for cold start running. Unles something has failed in the ECU, changing a bad ECT Sensor has to affect the ECU output.

Regards,
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Will Dallas, www.willdallas.us, www.willdallas.org, www.willdallas.com, www.dallasprecision.com 86 245 DL 222K miles, 93 940 260K miles, 88 765 GLE 152K miles, 88 780 246K miles