So sitting at traffic lights after my truck is fully warm, but outside air temperatures are in the 30's, it seems my grid heaters are cycling. The idle drops slightly in sync with the volt meter dropping. Is this normal?

Truck is a 97 with 55,000 miles. Thanks

 

It will cycle off the info it rec's from teh IAT sensor. If the temps are cold enough from the reading , the heaters cycle til its up to temp.

Temp's in the 30 will do it. Is your water temp coming up? A bad thermostat will stay open and keep it too cool with outside temps below 45F or so...

 

Water temp is coming up like normal. That makes sense though, both times it happened the truck was warm, sat for 5 minutes while I was in a store, than did it on my way home. I just never noticed before.

Thanks for the reply

 

I'm not sure this is normal. It would have to be really cold out for the grids to cycle while the engine is operating. Whats the engine temp when this happens?

Here is a couple links for you which may help:

http://dodgeram.org/tech/dsl/FAQ/cold_wx.htm

http://dodgeram.org/tech/dsl/trouble...niford_htr.htm

 

I'm starting to also think its not normal, happened yesterday when outside temp was around 45-50 f.
The temp is in the normal range of being warm, it happens after the truck was running for say a half hour, than shut off, than ran again. Like if I went into a store or something.
When I searched the Internet I did find something interesting about it being associated with a low washer fluid, how I don't know. My low fluid light was on when it was happening, I filled it up and it hasn't happened since.
Could it be a bad air temp sensor for the grid heaters?

Thanks for the reply and the links

 

Washer fluid.....? Have to remember that.

Also, just noting that if the grids are cycling after a restart then thats normal. The ECM will cycle the grids for a minute or so post startup even on a hot engine when the ambient temps are around 60* or colder. This warm engine post cycle is considered unnecessary but nonetheless, its normal. So if this is what you're experiencing then you're OK.

 

Where is the sensor that determines engine temps and reports to the ecu that then decides it's time to turn on the heater grid?

 

I believe what the ECM uses is a combination of the IAT sensor (registering the intake temp), the coolant temp sensor, and the overhead display outside temp which comes from the sensor mounted just in front of the radiator and behind the grill.

Definitely if the ECM reads the ambient temps 60* or cooler then the grids will cycle when the engine is cold, and even on post warm engine start up. But if the IAT and engine temps drop to a certain point while the engine is idling, then I believe that the grids will cycle. But as I mentioned, it has to get pretty cold out for this to happen. Its also what triggers the three cylinder high idle function.

 

mine were coming on at any time, and got stuck on and drained the battery.

So yes they can and do come on after starting for a minute or so in cold weather. but anything more then that and you may want to check it out a bit better.

 

Been a long time ago but when one of my trucks was new the low washer fluid light made my ABS light come on too.
My solution has been too not let the fluid get low...

 

I'll have to keep a close eye on that blinker fluid too.

 

It is the IAT (Intake Air Temp.)sensor. Located at the driver's rear of the head, above and behind the LP. It takes a 13/16" deep socket to remove and has a two pin connector. The first one you usually find in this general area is the MAP (Manifold Absolute Pressure) sensor. The IAT is further back at about the same height.

The other info comes from the water temp sensor, which is at the front of the engine.

A shot of electrical parts cleaner will do it...

 

How do you all know that your heater grid is cycling?
I see the light in the dash. Noticably "click" when it goes off and the dash light goes off.

Start the truck, and then...how would you know if/when it cycles again?

 

The voltage drops to the left side of the gauge...

 

Like the a/c compressor cycling when the defroster is on?
Or more dramatic?

I've seriously never noticed this. If I did, always just thought it was the a/c compressor cycling.