I noticed a weird issue with the grid heaters on my truck.

When the temps fall into the twenties or less, the grids do come one, as I can see the volts on the guage drop and I hear the relay click, then relase when the wait to start light goes out.

I start the engine, and then there is no cycling with the grids.

If the ambient temp is above freezing then the grids will cycle.

Is there a temp sensor that may be going out?

Thanks!

 

The temperature sensor only tells the box to start the sequence which is pre-programed. My best guess is you have a problem in the box. Something effected by temperature like a cold solder joint or cracked trace on the board.

 

Where would that box be located on a '90, since there is no ECM?

 

Still an ECM/PCM or whatever you want to call it. It is behind the battery. It's the same one used in the 91.5 with a manual.

 

Theirs two relays on left fender maybe one of them went out.

 

That wouldn't have any effect on when and how it cycles.

 

Ok, cool! Thanks for the info.

Temps were in the 40's this morning, and grids worked like normal.