Engine/Transmission (1994 - 1998) 98 12v killing batteries- grid heaters?

[dlefebvre]

We have a problem with my friends 98 12 valve killing the batteries when it is not running. He got back in the truck after a day at work to find the "wait to start" light clicking off and on and both batteries pretty much dead. I fugure it is maybe the grid heater relays, but if they click they are working, right? What would cause it to pull current with the key off? The problem started a week or two before when driving in the dark, I noticed the headlights flickering. I pulled the leads off the grid heaters, we charged the batteries and he has had no problems since, but it is getting cold here now and he needs the grid heaters back. Any help at all would be greatly appreciated.

 

[WDaniels]

Seriously doubt it. You probably have another draw somewere else. The grid heaters or their connections would burn up if there were on for 10 or 15 minutes solid. Besides, if they stayed on all the time you would see that when you started the truck in the ammeter. It would stay drawn down between 8 and 10 volts all the time.

WD

 

[kentdiesel]

One of the grid heater relays stuck on my truck and drained both batteries. I unhooked the wire that corrects the bad relay to the grid heater so right now I'm down to one grid. I plan on installing new relays soon. I should of known a relay was going bad because the head lights starting flickering. I thought it was a bad connection but it was the bad relay turning off and on as I went over bumps. I feel very lucky the truck didn't burn up, you could look at the wire end cover and tell it got hot.

Kent

 

[Skydiver]

My grid heater relays were sticking about 5 years back. The volt meter would remain around 10. 0 for 3 miles then the "Gen light" would come on. I would have to remove a cable from both batt's to reset computer. Not sure but I think it was the computer causing the problem, again not sure.



To correct: I pulled 1 wire from each relay that is until it drops below 25 degrees. Smokes bad when below 45 degrees. I always plug in block heater when below 50 if possible. Just testing I did start my cummins at 23 degrees with 4 seconds on the starter and no grid heat or block heat. I always add 1/2 inch of pedal when starting.



Our "True diesels" do not need help starting, but grid heat helps and keeps the smoke down. .

dlefebvre,your friends problem sounds different from mine. Could be bad relays or another cause killing batteries.

 

[Howard Durand]

The grid heaters get power from the batteries directly through the relays. The relays are not energized until the ignition key is turned on. They do not close until the PCM switches the ground lead for each relay. Your friends problem is most likely a stuck relay.

If the contacts on either of the grid heater relays is stuck or welded, that grid will remain energized, even with the key off.

The heater cables are fed directly from the battery through the relay. They either have fuses or fusible links to protect them.

Unplug one of the small wires connected to each of the grid heater relays. This will keep them from operating. If a grid heater still has voltage on it that relay is probably bad or possibly a short in the relay ground wire.

 

[kentdiesel]

If the contacts on either of the grid heater relays is stuck or welded, that grid will remain energized, even with the key off.

.

That's what happened to me, I turned the truck off when I got to work not knowning a relay had stuck. When I came out that evening the batteries were totally discharged.

 

[DieselDoghouse]

HMM! I smell a monitor tap off each grid heater stud back to the dash for a set of those new LED dashlights to monitor each relays status. Would look kinda nice flashing on'off at startup. Or mebbe I just git too much solder smoke in my head!!

 

[Katmandu]

Is there a thermostat for the grid heaters or are they on a timer ??

 

[Joe G.]

There is an air intake temperature sensor. If it is bad it would cause excessive use of the air heater grids. However, even a bad AIT will not cause the PCM turn on the heaters if the key is off. You need to get a volt meter and see what is going on.

 

[Katmandu]

There is an air intake temperature sensor. If it is bad it would cause excessive use of the air heater grids. However, even a bad AIT will not cause the PCM turn on the heaters if the key is off. You need to get a volt meter and see what is going on.

Where is the AIT sensor located on a 98 12 Valver ??

I did install a BHAF a few months back. Would that have anything to do with the AIT sensor ??

What controls the cycling of the grid heaters ???? Is it dependent upon the Air Temperature or is it on a Timed Circuit ???

 

[Joe G.]

If it's located the same as my '95 it's on top of the intake manifold between the air horn and the fire wall. It has two wires on it.



The PCM turns the grid heaters on if the AIT detects a temp below some value. I think it is 59° on my '95.



It's a better idea and will probably cost less to get your meter or circuit tester light and see what is going on. Just throwing parts at a problem is never a good idea. First thing is to unplug the AIT and see what happens.



This sort of thing is why you should have a service manual. The problem would have been solved already with the information in it.