Thorwon

I have a 91 Cherokee with the 4.0L. There are two temp sending units on the engine. the single wire unit at the rear of the head is for the light/gauge. What is the front unit for? Is it for the fan only or does it tell the computer when to go into closed loop?
This is my first 4.0L and I'm just trying to learn how the fuel injection works.

Turbo X_J

The coolant temperature sending unit relays the coolant temperature to the PCM.

ElMartillo

My understanding is that the fan has it's own thermal switch in the radiator. The coolant temp sensor toward the front of the engine provides temp info for the computer.

Brett Parks

why can't one sensor do both jobs? Why need two separate sensors?

CCKen

Because it's a pre-97 XJ.

BlueRidgeMark

In other words, because, dumb.