Tmello401

Hello I have a 96 12v and it recently started having problems starting now that it has gotten cold. I replaced my relays for the grid heaters two years ago and figured they went bad. I tested for power on the relays with the key on and wait to start light on and nothing. So I replaced them with a whole new assembly and the grid heaters still do not work. They used to work fine before the truck started and after. Does anyone have any ideas thanks a lot.

patdaly

You should have 12V all the time to one side of the large posts and 1 side of the small posts. Check the wires leading from the battery to the GH solenoids.

The way it works is the IAT ( Intake air temperature ) sensor reports the IAT to the PCM, the PCM decides if it sees less than 61 deg. F, it turns them on by dragging the other small to ground ( at least on our year trucks, I think it changed the other way in 2001 ) and turning on the Solenoid.

So make sure the fusible links feeding the solenoids are good and 12V present at all times, then let us know what you find.

texasprd

On my '96, it has to be about 50 degrees to trigger the heater grids at start-up, so consider whether the temps are cold enough for your particular vehicle. I saw, sometime ago, a post on another Dodge CTD site that showed someone tricking the PCM into turning on the grids by using a 50K-ohm potentiometer in the circuit from the IAT sensor to simulate temperatures cold enough to need the grids. Ss far as I can tell from the pic, he just put the ends of the wires from the potentiometer into the IAT sensor plug. Consider this as a testing technique.

KATOOM

Instead of typing and typing..... Here's is all the information you need to diagnose your grid heater system. Its not that complicated either, even though there's lots of wires and parts.
Ram Diesel Manifold Heater Problems

SIXSLUG

Which relays did you get? DID you test then with a multimeter?