I'm new to the forums.. I'm an up and coming DIYer. I bought a 03 2500 (5.9L Cummins) a few months ago and have 2 glitches I need to work out.

1. I suspect the grid heater is cycling in cold weather. The truck won't start when it sits for 5-8 hours in cold weather. I tested the continuity of the grid heater like a friend told me and it was ok. But I'm not getting any voltage to the grid heaters during the pre-start cycle. I traced the wiring back to the relays on the left side of the engine compartment, by the battery. So how do I check and see if they're ok? Also, where is the fuse for this circuit?

2. My master switch operates the passenger windows, so I know the motors are working. But the individual passenger window control switches don't work. I checked the fuse and it looked ok. I popped open the passenger side panel piece and checked that the wiring was connected. Anybody got any other ideas??

Thanks for any help, in advance.

 

Moved to Cummins Diesel section for better replies.

 

Thanks for moving thread. Sorry I put it in the wrong section.

No replies yet?? What's the deal folks? It's winter time and I need help!

Ok. In the process of narrowing down my grid heater problem, I've checked both relays and they're good. I checked the grid heater for continuity. Continuity to ground and studs is correct. Relays have power. I'm about to check to make sure power is getting from the relays to the heater + terminals. What I think I've narrowed it down to now is an Air Temperature senser problem. The manual that I have doesn't really help me find the sensor. Any tips?

Also, I have a very suspicious electrical connector that is just hanging loose near the driver's side battery. It seems like it wouldn't have been there if something weren't supposed to be connected to it. I've looked all around and can't find a spare female connector hanging loose anywhere. Does anyone know if this could be related to the grid heater somehow?

 

the plug is probably for some option your truck didnt come with, how cold is it during the no start situation? does it only do it below a cirtian temp? the window, i would suspect the switch has failed in one of the doors

 

When the truck does start, do you see your lights dim/ get bright repeatedly? The grid heater should cycle when the temp is below 57-59 degrees. Do you have a quad cab with 4 operating windows? Are all 3 passenger switches not working? There is a lock-out switch on the drivers master switch that will prevent the passenger windows from operating on their own switches.

 

Hey thanks for the reply. You're right about the connector. My friend pointed that out a little while ago too.

The truck isn't cold starting below 60 degrees unless I plug in the block heater, in which case it has started at about 30 degrees. I'm in Alabama so it has only gotten down to about 20 degrees at night so far.

My dad and I just did some more testing, and found that the relays are getting 12Vs to the signal wires and are getting good voltage from the battery. They are clicking. However, the heater isn't getting voltage (but has continuity). When we bypassed the relays the heater did operate. Which leads me to now conclude that the relays must be stuck closed or something. I'm going to order replacements tomorrow and pray that it fixes the issue.

As far as the switches are concerned, I'll go down and check them again, but I'm pretty sure the door lock buttons work but not the window buttons...? The switch only has one connector for all wires.

 

I know I'm double posting here.. but I saw your reply after my last post.

Quad Cab. All windows work from the master switch, but three passenger windows don't operate from their individual switches. Lock out button is not pushed down. Please review my last post. I checked the passenger switch, and the door lock button works, but not the window switch.

And when I turn the switch to the on position, and the wait to start light is on, no voltage is drawn to the grid heater, which I think is what you're asking.

 

What I'm asking you to look for is the interior dome lights. When the grid heaters are working you should see the dome lights dim then "get bright" the same time the wait to start light goes out. Also, you should see your voltage gauge move when the wait to start light goes out. We are trying to help you figure out if the heater is actually working or not. I'm trying to show you the easy way to see if you grid heater is actually working. You don't need any meters to do the tests I'm asking. That's what makes it easy.

As far as your windows. I still say the problem is your lockout switch on the drivers door. It may have gotten wet or something. I highly doubt that you have 3 bad window switches.

 

Thanks for the reply Brian. You're right, it does seem like the lock out is pressed down, but I promise it's not. It could be the switch. I bought a used master switch off a truck right after I bought mine, thinking it would fix the issue.. but it didn't. I guess it's possible that the one I bought is messed up too.

As far as the heaters are concerned, after replacing the relays:
1. I left the truck unplugged that night.
2. It was about 33 degrees the next morning when I went to start it.
3. I pre-start cycled the truck twice. (The wait to start light only stayed on about 5 seconds, and the book said it should stay on like 15 or 20 seconds at that temperature)
4. Cycled the "Wait to start" light twice.
5. Truck didn't start after two tries of about 10 seconds.
6. I have two brand new 850 cold cranking amp rated batteries. Battery voltage may have dropped a little but not a whole lot, maintained right at 12V I think.
7. Interior lights did dim for a few seconds, go bright, then dim again a couple times.

I hope this helps someone help me. I don't care about the windows.. I just want these grid heaters figured out. I'm just worried that the sensor has gone bad or something.

 

sounds like a possiable manifoild ait temp sensor issue, if you know some one that has a programmer with the data logging option, pulg it in and see if the temp looks correct