Volvo: S70 Coolant sensor, coolant temp, poor connections

Question
The check engine light comes on and code is coolant sensor had new one installed a week  went by no more than 200 miles and check engine light came on again with same problem
What could be the cause and what could be done?

Thanks

Answer
Richard,
You may have a defective sensor, poor connections or wires. or a bad control unit. Start taking the readings on the scanner as the car runs see that the temp is in fact rising as the car warms up. Most times I also replace the T/stat they will sometimes cause a hot or cool running engine that will also set a coolant temp sensor code.