Coolant temp idiot light stays on, on start up.

Hot Air Beast

Hot Air Lover
Mar 10, 2007
After driving for ten minutes and being parked for 30, my 1984 GN would not start. After a few tries, it started and drove fine for 10 minutes to home. Next morning, would not start again. Pulled code 15, "abnormally low coolant temperature". This code causes the fuel to dump. I changed the sensor and the car started right up. I thought the problem was solved. An hour later I started it again and the idiot light on the dash came on and stayed on (overheat light).

Could this be a bad sensor out of the box, or should I be looking for something else? The only wire that was moved was the connection to the sensor.
Early 84 cars had a problem with the 1-wire coolant temp sensor. They'd fail, coolant would work its way into the ECM through the wire itself, and cause damage to the ECM connector.

Check to see if you have the 1-wire sensor instead of 2 wire.
Interesting John; however, the one wire is totally outside the sensor and is only a male/female quick push-pull connector with no coolant travelling outside the sensor. Don't suppose Caspers sells a better than NOS one wire sensor??
That's what was strange about that connection; the wire would pick up coolant in the center, not leak outside. Look at the ECM for signs of coolant in it.
I will have to do that. There are two sensors and I mistakenly changed the one wire one which only drives the dash light and mine is on top of the intake beside the thermostat housing. I understand the two wire is below the housing. Going to check everything in the morning. Thanx.