Volvo Repair: 2001 Volvo S40 Coolant temperature sensor, coolant temperature sensor, 2001 volvo s40

Question
I have a "Check Engine" light on a 2001 Volvo S40.  The code reads "Coolant temperature below thermostat regulated temperature".  I have replaced the thermostat and have done the drive out (7min @ 2000rpm, 2min @ idle recommended by a volvo mechanic) and the light did not clear.  How do I check the coolant temperature sensor and where is it located.?

Answer
You're going to need a scanner of some kind to clear the code for the light to go out.  It will not go out with just one drive cycle.  It is usally the thermostat that causes that problem but temp sensors have gone bad.  To check it read voltage on signal wire of temp sensor (located under thermostat housing, connector for sensor is on top of power steering pump very obviously located).  It should read 2.6 volts at 26 degrees celcius (basically room temp), and read 0.6 volts at 100 degrees celcius (operating temperature).  It is not too expensive so you may just want to replace it anyways.  Also if the ECT has gone bad (open or short circuit) so that it reads full max or full min temp the cooling fan will be running all the time regardless of engine temperature.  The gauge for temp on the dashboard also gets its signal from the same sensor so thats another thing to check.  Hope that helps.

James