1999 Chevy Cavalier Check Engine Codes

We had a code that indicated "Cylinder Head Temperature Guage" and took it to be replaced. Instead, they put in a "Coolant Temperature Sensor" saying that it was the same thing. The coolant temp never changes now and the check engine light is on again and STAYS on but with a new code--> 0118 UIF which reads as "Engine Coolant Temperature High Input". Also, the car shut itself off when started- while warming up. Please explain whether or not cylinder head temp guage and coolant temp sensor are same or NOT and then what this newest code means before we spend any more money on something that won't help. When the car is driven: either warm or cold/different speeds - at times it seems to shudder (sometimes worse than others) as though it's going to die but then seems fine.
My college age daughter is driving this and I am concerned for her safety but can't afford to be strung along with incorrect repairs either.