Check Engine light is ON and Coolant Temperature reading is showing nothing

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Hello, Currently my car`s check engine light is ON. It actually comes and goes. But whenever check engine light is ON, coolant temperature reading showing nothing (It shows dashes). Sometimes same thing happens for tire pressure readings too, it shows dashes for tire pressure but at light time it does not show check engine light ON. What could be the probably cause for it? Do I need to change coolant or thermostat or anything else?