Aeby711

On my 03 5.9 my grid heater is not heating. I replaced the two relays. I have jumped 12v directly to the ecm wire terminal and the heater heats up. I have also tested the two fused wires that are direct from the battery to the relays.
When I turn the key on I will have 12v at my ecm wire for only 3 seconds and is drops to 3.5v and stays there. Can anyone help?

KATOOM

Sometimes its a corrosion issue. Even though I dont live where road salts are used, when my grid system acted up I traced everything down, as its a pretty simple system, but still couldn't find anything not working. I even tested the IAT and battery temp sensor to make sure they weren't causing the system to recognize a conflicting ambient temperature.

Eventually I discovered that the short ground wire from the grid heater to the manifold had a slightly corroded crimped fitting which was just enough to screw up everything. Pulled the wire off, cut it about 3/8" shorter, re-crimped the fitting, shrink tubed the end, and all is good.

Aeby711

Thank you for the reply. The ground wire is ok.
When the engine is cold and key on I have 12v at the grid heater but only for 5 to 10 seconds and then the voltage drops to 3.5 and kicks the relays off. I assume it needs to keeps 12v longed to heat things better. Any thoughts?

KATOOM

Depending on the ambient temperatures, the grid heaters cycle initially based on that temperature.
I know this link is for the 2nd gen trucks, but I believe the grid heater system is relatively the same. Might help you understand how its supposed to function. Ram Diesel Manifold Heater Problems

Aeby711

Thank u for the link to the intake heater test procedure.
It was very help full until I got to where it wants u to test the ohms between the two threaded studs on the heater to ground because the heater is grounded on the other end. Anyway when I tested the heater I had ohms so I changed it out and still have continuity from ground to the studs on the new heater?

KATOOM

You should disconnect the heater element from the grounds when performing the resistance test. If you're unsure about your test results then go buy a new one and test them side by side. If the new one is doing the same as the old one then the old one is probably fine.

Aeby711

Thank you for all your info you have shared. I'm confused.
on my 03 what is the air intake sensor that controls the air intake heater relays?
is it the map sensor also? Or is it another sensor elsewhere?

KATOOM

I'm sorry but my knowledge of the 3rd gen trucks only goes so far..... I'm sure its similar, or possibly the same, as the 2nd gen whereby the ECM takes the information from the ambient temperature sensor up under the grill, the IAT sensor, and the battery temperature sensor under the drivers side battery. If all parameters are met to recognize that the ambient weather is less than 60*F then the grid heaters cycle. The time duration of the cycle is dependent on how cold that ambient temperature is.
Maybe someone more understanding of the 3rd gen grid heater system would confirm if thats accurate.