Engine/Transmission (1998.5 - 2002) Grid heater won't shut off

[SOOT]

Some mornings I will stop at a convenience store on my way to work. After I start the truck if its cool enough for the heater to cycle, it wont shut off when i get up to speed(55+). It keeps ccycling for several minutes. What controls when the heater cycles?

 

[SAndreasen]

Mine shuts off at 20 mph no matter how cold it is . The intake Air temperature sensor is what tells the ECM to send power to the relays that then make the grids work so if it's below a certain temperature it will cycle the grid .

 

[DennyDay]

When I had an '03, the grid heater ran a little long, so I installed a pressure switch (from an auto parts store) on the oil filter mounting bracket. Switch opened a ground that I ran to the grid heater in place of the OEM ground, and as long as there was oil pressure, the grid heater did not operate. Tried to Install the same thing on my '06 and it wouldn't work as the sensor put a code up.

 

[SOOT]

Thanks for the replies. I was in a hurry when i posted that. I know the IAT tells the ecm when to cylce the heater, i was just wandering what would not be working properly for the ecm to not shut it off when getting up to speed. Its always worked fine until recently, i haven't made any changes to the truck in a while so it's not something i did. Atleast not this time. Can't be good on the alternator to be working that hard for that long while driving. I might just unhook it anyways, since i now live in south Texas.

 

[FourBarR]

sticking IAT relays. There are two located on the drivers side just below the battery. One is for the lower heater and one for the upper. they cycle alternately .

 

[SAndreasen]

My relays worked good all winter then started sticking the other day so I unhooked the grids for now . That's probably what caused the original grid to break