Engine fan for 1998 379 pete

Ok first thing that sensor up by the radiator is the high presure fan switch. If you unplug it when working on a system that is working properly the fan will come on. If you jump it it will go off but depending on how the fan timer is set in the ECM and that meaning the time the ECM lets the fan run everytime it cycles with the AC and comes on. Say if your timer is set for 2 minutes in the ECM then you would have to have that jumper wire connected across both terminals on the plug side which is part of the truck harness to get the fan to cycle off. Don't jump the sensor but jump the two wire plug connector that plugs into it. Then see if it will cycle off but is sounds like what ever this fuse powers up is the problem because it won't turn off at all with it plugged in. Is that right. If it is, you need to know what circuit that is dealing with and without some kind of PB schamatic Im not really sure unless it is disabling the fan air switch that turns it on and off up on the firewall Im not sure why that fuse is playing a part in this for sure.

 

The newer hortons usually take air to turn the fan off this disengages the clutch so it don't turn with the hub. Then when you take the air away it wll lock the clutch and make it engage or turn the fan on. You could have one that works opposite but it shouldn't be on that year model of truck and engine.

 

Hi, first things first. Your fan is not completely controled by your ecm. In fact most functions do not go through the ecm and the trucks are not wired that way. We see lots of issues of people trying to program them like they are though. Your truck has fuses and relays behind the dash for the engine fan. Most likely one of the 10amp ones is out. If you pull your panel with the speedo the fuse block is mounted twards the right on a metal crossmember. I have attached a diagram for you. The Cat engines were NOT wired like a Detroit or Cummins of that vintage.

 

When you pull your fan contol relay do you have fused power on 223? If you pull your relay does the fan stay running or turn off? One big thing to note is the fan control relay is normaly closed. I personaly believe you have a wiring issue and doubt your ecm is bad. There are lots of things that could trigger the ecm to turn on the fan if that is the case. You should see a good experianced tech at a Pete shop....

 

I would wonder about that 9.5 volts. Make sure you have good 12 volts power and ground to the ecu. Any ecu power problems could cause all sorts of issues. You may have wire 522 shorted to power on another wire. Your ecm should put out 12 volts if it wants the fan on. Pull the ecm connector and the relay, use a ohm meter to check between wire 522 and all the other wires and to ground. You could also pull the pin 28 (522 wire) out of the connector if you have the tools to do so. Then see if the fan still comes on or if you have the voltage. If all the wiring checks out good you need to have a good Cat guy at a Pete shop (Alot of people get these older Cats wrong trying to program them like other brands or newer trucks) hook up and check parameters to make sure its programed correct. Then moniter and see what parameter is turning the fan on. Many more things can turn on the fan other than just coolant temp, A/C high press, or manual fan switch. Good luck.

 

most often over looked is the intake manifold temp sensor, stuck in range so you wont get a check engine light but it will turn the fan on to cool the intake temp change it out and the fan will go off