Chrysler Repair: 97 Dodge Neon: code 31, coolant temp, haynes book

Question
I need to get my car inspected but engine light is on.  did the test to get trouble codes and got code 12 and 31. i just need more info on code 31 i i cant find anything in the haynes book about what it is or were it is located. if you could help me that would be great.

Answer
Hi Jen,
That code means that the engine coolant temp sensor voltage is too high, which is either that the sensor has gone bad or the wiring to it has a short circuit. The sensor is located at a different position depending upon whether you have the SOHC (located on the rear of the engine) or DOHC (located near the thermostat housing on the front top of the engine). You can remove the plug from the sensor by lifting the tab and that will allow you to measure the resistance of the sensor when the engine is cold and when it is warm. There are three terminals arranged in a "T" configuration. measure between the 2 terminals that constitute the crossbar of the T. It should read about 4,000 ohms when the engine is cold and 700-1,000 ohms when at operting temperture. If not close to those values then change the sensor. If it is, then check the wiring harness for signs of damage to the insulation and repair as necessary. Let me know if you have questions or the things you find are a puzzle. It simply unscrews but before you do that you would do well to drain off a quart of coolant from the system via the radiator draincock so that the level of the coolant in the engine will be below that of the sensor when you remove it.
Roland