OK..... It has been about 30 to 40 degress F around here lately and I have had the truck in the mountains down to 5 and the heaters won't cycle. Can someone give me step by step instructions about what to check first to last. I know the IAT and I think the battery temp sensors (?) control the grids to come on. I pulled the IAT and it was dirty. I cleaned it off with a type of non-residue cleaner (like a break cleaner) and replaced it. It did not change anything. The light will come on for a few seconds (2 or 3) and then go off and stay off. I know this has been covered and I have spent the last 1 1/2 hours trying to find everything I need to check. What are the volts to the heaters (12?). The truck is getting very hard to start now with temps in the 30's. It idles very rough and lots of white smoke. When I was in the mountains hunting, I could not get it to start until it wamed up (the batteries were low from having my trailer plugged in to the truck and running the heaters in the trailer all night. )
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Archived Grid Heaters Again
- Thread starter FFL8N
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Do you have the factory service manual for your truck? The heater grids on model year 2000 Cummins/Rams have, for the most part, independent circuits. Unless you have had two parts of the circuit fail, it's likely that your problem is in something common to both heater grids. If you remove any wires from the relays, don't mix them up when reattaching.
Easiest thing to check is the pair of 6 gauge wires from the relays (beneath driver's side battery) to the driver's side battery. These wires go through separate fusible links before they join and attach to the positive battery post. You should always see 12 volts at the relay ends of these wires.
Each relay will have three more wires attached—two small and one large—that go into a harness. The large wire goes to the heater grid. The two smaller wires are the trigger wires for the relay. One goes to the ECM and the other (black/tan) goes to joint connector #2 in the PDC and then to ground. The two relays are triggered by different pins at the ECM.
If the relays don't "click" when the key is turned on during cold conditions I would remove a black/tan wire from one of the relays and check for ground.
Easiest thing to check is the pair of 6 gauge wires from the relays (beneath driver's side battery) to the driver's side battery. These wires go through separate fusible links before they join and attach to the positive battery post. You should always see 12 volts at the relay ends of these wires.
Each relay will have three more wires attached—two small and one large—that go into a harness. The large wire goes to the heater grid. The two smaller wires are the trigger wires for the relay. One goes to the ECM and the other (black/tan) goes to joint connector #2 in the PDC and then to ground. The two relays are triggered by different pins at the ECM.
If the relays don't "click" when the key is turned on during cold conditions I would remove a black/tan wire from one of the relays and check for ground.
Both my heaters were inoperative. Both relays were bad. I bought 2 new ones from Allied Electrical. Way cheaper than the Dodge dealer.
Check a few things first before condemning the relays though.
The relays look a little like starter solenoids, and are located on the left fenderwell, lower than battery tray level. They'll have 2 big wires and 2 small wires.
The relays are ground-side triggered. That means the control side of the relay has power all the time and the PCM supplies ground to the relay to make it work.
On each relay one of the big wires will have power all the time. If not, follow that wire to the B+ on the battery right above it to find the problem.
One of the small wires will have power with the key on, the other is the trigger wire for the relay. When that wire is grounded the relay should click on, and put 12V on the wire going to the heater grid(the other big wire on the relay). If it doesn't then the relay is frozen and needs to be replaced.
Hope that helps.
Joe
Check a few things first before condemning the relays though.
The relays look a little like starter solenoids, and are located on the left fenderwell, lower than battery tray level. They'll have 2 big wires and 2 small wires.
The relays are ground-side triggered. That means the control side of the relay has power all the time and the PCM supplies ground to the relay to make it work.
On each relay one of the big wires will have power all the time. If not, follow that wire to the B+ on the battery right above it to find the problem.
One of the small wires will have power with the key on, the other is the trigger wire for the relay. When that wire is grounded the relay should click on, and put 12V on the wire going to the heater grid(the other big wire on the relay). If it doesn't then the relay is frozen and needs to be replaced.
Hope that helps.
Joe
"The relays are ground-side triggered. That means the control side of the relay has power all the time and the PCM supplies ground to the relay to make it work. "
The truck with the problem is a model year 2000 ISB Cummins. The trigger circuit for the heater grid relays on the 24 valve engines is spelled out in the third paragraph of my post above. One side of the trigger coil is always grounded (black/tan wire) and the other side of the trigger coil receives its signal from the ECM.
The truck with the problem is a model year 2000 ISB Cummins. The trigger circuit for the heater grid relays on the 24 valve engines is spelled out in the third paragraph of my post above. One side of the trigger coil is always grounded (black/tan wire) and the other side of the trigger coil receives its signal from the ECM.
FF1607, a couple of questions.
Does the "wait to start" light only stay on for the 2 to 3 seconds?
When you cycle the key do you get a voltage drop on the voltage gauge during the cycle?
If both are true I would suspect the IAT to be bad.
You can use a ODB scanner to look at the temp. being reported to ecm and pretty much tell by the value if it is.
No ODB? Buy the IAT (not too much money) and give it a go.
Mike
Does the "wait to start" light only stay on for the 2 to 3 seconds?
When you cycle the key do you get a voltage drop on the voltage gauge during the cycle?
If both are true I would suspect the IAT to be bad.
You can use a ODB scanner to look at the temp. being reported to ecm and pretty much tell by the value if it is.
No ODB? Buy the IAT (not too much money) and give it a go.
Mike
ooops!
I was mistaken... . The wait to start light does stay on the the normal amount of time..... 10 seconds maybe... It doesn't matter how many times I cycle the grids, I get the same result. This morning was the worst yet, except for when I was hunting in the mountains. It wasn't wanting to start. It started on about half the cylinders it sounded like and almost died until the rest caught and then the idle smoothed out. By the way, I don't have the cold weather start added to the truck.
I also did check the wires first to make sure they were tight. No problems there.
Any more help, before I start checking for power and probing my truck???
I was mistaken... . The wait to start light does stay on the the normal amount of time..... 10 seconds maybe... It doesn't matter how many times I cycle the grids, I get the same result. This morning was the worst yet, except for when I was hunting in the mountains. It wasn't wanting to start. It started on about half the cylinders it sounded like and almost died until the rest caught and then the idle smoothed out. By the way, I don't have the cold weather start added to the truck.
I also did check the wires first to make sure they were tight. No problems there.
Any more help, before I start checking for power and probing my truck???
The trigger coils of the heater relays are attached to different pins of the ECM. While not impossible, I think a failure of both ECM connections is unlikely. The common part of the trigger circuits is the ground. The ground is easily checked. The 18 gauge black/tan wire at each heater relay should always be connected to ground.
Hi Thomas,
My mistake on the ground side switching. My '96 is wired like I posted. What year did it change?
AKAMAC, if the light is coming on like it should check the relays. If you disconnect both small wires to the relay, supply 12V to one side of the relay and ground to the other it should click on. It should only take a minute or two to try that.
Joe
My mistake on the ground side switching. My '96 is wired like I posted. What year did it change?
AKAMAC, if the light is coming on like it should check the relays. If you disconnect both small wires to the relay, supply 12V to one side of the relay and ground to the other it should click on. It should only take a minute or two to try that.
Joe
JoeBiodiesel... ... do you have a part number for the relays?? Also, how about a contact number for allied electrical. If I find out that is the problem, I would like to get the best price I could find. Thanks... ... I haven't had a chance yet to start looking for the problem, but anymore sugestions out there... .
I do have the factory service manual for my truck Thomas... Just not much of an electrical guy... . I do have a good voltmeter though. I will try to figure the wires out. The black and tan 18g wires..... are there two of them... one to each relay... then there was a red wire and another colored wire... . I don't remember... . one to each seperate relay also, right?
I do have the factory service manual for my truck Thomas... Just not much of an electrical guy... . I do have a good voltmeter though. I will try to figure the wires out. The black and tan 18g wires..... are there two of them... one to each relay... then there was a red wire and another colored wire... . I don't remember... . one to each seperate relay also, right?
Wait! Before you condemn the relays, check the two 12 gauge fusible links right off the battery first. There are two of them, one for each heater. One or both could be blown, causing the heaters to be inoperative.
If they check out ok, then move on to checking for high resistance from the ground lug on the heater assembly to the intake manifold. If that checks out ok, check the relays. Make sure they got good ground and trigger connections. Then check for a voltage drop across the relays when they are activated.
If there is an open circuit in the trigger side of the relays, it should set a P380 or P382 code, depending which circuit is bad. It won't indicate whether the heaters are good or bad though.
On my '01, I added LED pilot lights to the intake heaters so I could easily monitor what was going on. Since I have a 6-speed, I mounted the LEDs in the knockout where the automatic transmission indicator usually resides. However, I did disable the heaters about a year ago, because they are just not needed. It gets fairly cold at night sometimes (mid-20s), and the thing lights right off with no problem. I have even had it sit overnight in colder conditions (teens), and it still fires right off. Smoke is minimal, and yes, it is running on all six.
Hi FF1607,
Here is a link to Allieds search page.
http://www.alliedelec.com/Search. ASP
You want two Stancor relays part # 120-902.
Search by manufacturer part # to find it easiest.
They just came off backorder. I have installed 4 of these in the last month. They all failed the same way. When you triggered them they didn't even click(and they normally click pretty loudly).
If you end up ordering these relays you will need to modify the stock bracket a little bit in otder to make it fit nicely.
I remove the entire bracket.
Bend the tabs at the base of the old relays, the relays will fall apart.
Cut the tabs off with a pair of side-cutting pliers.
File or grind the sides of the bracket where the tabs used to be, gring them the entire length of the bracket.
Bend the brackets on the new relays backwards around the old bracket. Put the bump on the bottoom of the new relays into the depression in the old bracket and they will stay in place nicely.
If you'd rather call Allied on the phone, their # is 800-433-5700.
Good luck,
Joe
Here is a link to Allieds search page.
http://www.alliedelec.com/Search. ASP
You want two Stancor relays part # 120-902.
Search by manufacturer part # to find it easiest.
They just came off backorder. I have installed 4 of these in the last month. They all failed the same way. When you triggered them they didn't even click(and they normally click pretty loudly).
If you end up ordering these relays you will need to modify the stock bracket a little bit in otder to make it fit nicely.
I remove the entire bracket.
Bend the tabs at the base of the old relays, the relays will fall apart.
Cut the tabs off with a pair of side-cutting pliers.
File or grind the sides of the bracket where the tabs used to be, gring them the entire length of the bracket.
Bend the brackets on the new relays backwards around the old bracket. Put the bump on the bottoom of the new relays into the depression in the old bracket and they will stay in place nicely.
If you'd rather call Allied on the phone, their # is 800-433-5700.
Good luck,
Joe
Last edited by a moderator:
Re: fusible links
Nope, not using block heater. Would like to, but there's no outlet close by.
Nope, not using block heater. Would like to, but there's no outlet close by.
OK... This is wierd..... Four day ago... . They came on on worked two mornings in a row... They haven't came on since and the temperatures have remained pretty constant... in the low 30's. Any new ideas? I still haven't checked anything yet... I have been busy with Christmas and New Years stuff.
Wow... do I feel stupid... First I would like to say thank you for all those who responded!!!!!
Next... like someone said... check the simple things first. My ground right off the heater was almost broke in half and looked burnt. I still need to find a better wire for it, but I put the thickest wire I had available on it and sodered the heck out of it. Now it works. Anyone know how I can get this wire. I called Dodge... of course its "Dodge" and they told me I would have to order the whole engine wiring harness to get it. NOT!!!! Anyway... Cummins can't find it on there books... local auto parts stores don't cary anything that thick... Looks like I will have to have a custom wire made!!
Next... like someone said... check the simple things first. My ground right off the heater was almost broke in half and looked burnt. I still need to find a better wire for it, but I put the thickest wire I had available on it and sodered the heck out of it. Now it works. Anyone know how I can get this wire. I called Dodge... of course its "Dodge" and they told me I would have to order the whole engine wiring harness to get it. NOT!!!! Anyway... Cummins can't find it on there books... local auto parts stores don't cary anything that thick... Looks like I will have to have a custom wire made!!
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Issue 128 – Digital Version
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FREE!
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Renew
Subscribe
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Back Issues
Subscription Status
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Buyer's Guides
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