Engine/Transmission (1998.5 - 2002) Intake grid air heater

[Steve Robinson]

I find my volt meter does not cycle charge/discharge etc. during cold morning start-ups. What generally happens is the volt meter shows a state of discharge until I have driven a shot way. I had the alternator checked and it is fine the tech in the generator shop said he thought the gauge was probably at fault. I don't know. I also replaced the two batteries but the condition continues.



My thought is, what ever mechanism cycling the grid heater on and off is not doing so and therefore, the heater is staying on and the volt meter is indicating the power use. Does this sound right to any of you? Also, what is the fix for this problem? Thanks for the help.

 

[Midnite]

Sounds like your grid heater relays are sticking maybe? That's an easy thing to test for--just swap them with others like the horn relay.

Mike

 

[Steve Robinson]

Thanks Mike, I'll try that.

 

[ALepley]

Can you tell if the tone of your truck changes? Thats a sign that they are working. All dodges seem to do that when the intake heater kicks on it kinda loads the engine and when it kicks off you can hear a difference in tone.

 

[Steve Robinson]

I don't detect any cycling on and off of the heater by looking at the volt meter as I used to be able to do. Also, I haven't noticed any change in engine noise, again, no cycling.
I am wondering if a multimeter could be connected to one side of the relay to see if cycling was indeed occurring or if the relay remains in a constant "on" mode? Have any thoughts about that?
I also took a quick look at what I believe is the heater relays, one each connected to each of the batteries, and they appear to differ from the horn relay so I don't know about swapping them as a check for a faulty relay. What do you think?

 

[Skydiver]

Place one VOM lead to the large grid wire that goes to the grid heater and ground the other VOM lead to check for voltage. Do this right after cranking the engine to see if they are cyclying. If they are stuck close and the engine is warm try tapping them LIGHTLY with a plastic screwdriver handle to open them up. You can pull one small wire from each relay to temp. disable them.

 

[Steve Robinson]

Thank you for the advice and I will give that a try tomorrow morning. Do you know the method by which the relays are signaled to close and open? I suspect it is a timer or a temperature sensor but really, I don't know. Certainly, the relays are nothing more than switches and ,as you say, sticking may be the problem and that will be my first check. Thank you again for your response and your help.

 

[Bob Cochran]

Thank you for the advice and I will give that a try tomorrow morning. Do you know the method by which the relays are signaled to close and open? I suspect it is a timer or a temperature sensor but really, I don't know. Certainly, the relays are nothing more than switches and ,as you say, sticking may be the problem and that will be my first check. Thank you again for your response and your help.

They are controlled to turn off/on by temperature via the ECM I think. And I believe once speed gets above I think 15 MPH(not sure about that number) then again ECM turns them off.

 

[CToney]

Do a search and you will find more info. The grid heaters are cycled according to intake air temp. One or both may come on. If your truck is plugged in (block heater for 4 or more hrs) they shouldn't cycle unless it is very cold or very windy. Relays are not cheap. I disconnect mine, trigger wire, so they don't cycle so much so that when I may need them they will work. Plug your truck in. It saves fuel and your engine.

 

[GHerrmann]

Are you starting the truck and driving it right away? Or are you letting it idle and warm up for a while? If I fast idle my truck while the heaters are running they will not cycle. I think if you are driving right away you may be pulling a larger volume of cold air. The heaters may not be able to keep up. The IAT may never see warmer air to cycle the grid heaters.

 

[Steve Robinson]

CToney and GHerrman, thank you both for your interest and input, vocationally, I am not well suited so you help is much appreciated. I'll attempt to address both of you responses.
I live on the coast of Southern California and so when I say "... cold morning start-ups" it is a relative statement. Cold winter morning may be in the high 40s or low 50s and I think plugging the truck in might work but it doesn't seem cold enough.

When I start the truck in the morning, or really anytime, I sit there and idle for a while. I watch the gauges until I have full oil pressure, scratch my head about why the volt meter is in so deep a discharge position and no obvious cycling is going on (I'll know more in an hour or so after I check the relays with my meter) and finally drive off. It normally takes a block or two until the volt meter begins to return to the charge position regardless of the engine speed or speed over ground.
As Bob Cochran surmised earlier, the signal to cycle may come from the ECM and therein I may discover the origins of the problem. I don't know, and ultimately, I don't know what that would mean in terms of repair. Do you guys have knowledge of the source of the signal which causes the relays to cycle? Anyway, first thing is I am on my way out to meter my relays and then I'll take it from there. Thanks to you both (and all others) for your kind input, helping me solve this