ECU MAL 13 and coolant Temp Sensor

[Roy]

I have a 1990 240SX that keeps giving me the 13 mal. Being I am yet without a service manual as the local stores are out, I am in need of finding out where exactly this coolant temp sensor is. I have one sensor next to the temp sending unit that attaches to the intake manifolds coolant passageway, and another sensor in the bottom radiator hose.

I am thinking the coolant temp sensor is the one in the manifold, but what is the one in the bottom radiator hose?

Could a bad coolant temp sensor cause excessive gas consumption and hard starting. I would have posted this in the 240SX forum but I am not able to wait 48 hours as rules state. I need to try and get this car working ok.