Other than an obvious external leak that you can easily see, you may have a blown head gasket.
The check engine light comes on for numerous faults found by the computer. You will have to have the code pulled to find out why it is flashing. Most auto parts stores will do this at no cost.
A PCV valve is for positive crankcase ventilation. It is to keep crankcase pressure from building up in the engine. If it does it can cause seal leakage, air filter contamination and engine blowby.
it is a defective speed sensor.
You have a bad Vss Sensor.............. The vehicle speed sensor.
Short in the wiring or inside one of the plugs.
constantly running your car with low fuel will burn out your fuel pump
The thermostat is just under the throttle assembly at the front of the engine. You will need to remove a black plastic shield in order to access it. Is it difficult to remove and replace? Should that job cost $100? Would a failing thermostat cause the radiator to crack,leak and overheat on my 1991 Acura?
an airbag warning lite (srs)can be cuased either from a censor or a major problem
you might have a bad Flasher relay.
check the brake light switch behind the brake pedal under the dash.
There are pages and pages of things that can cause a check engine light. You need to have it checked with a scantool. Then the code can be diagnosed and repaired.
After repairing the cause of the code, you reset it with a scan tool.