Engine/Transmission (1994 - 1998) Grid Heater sticking on. Troubleshooting help needed.

[mtarcher1]

My '95 Ram grid heaters seem to be sticking on. I first noticed a hot electrical smell (not real strong, but noticable) a couple of days ago on a cold start. I shut it down and tried to find the source but couldn't really zoom in on anything. I felt the alternator and it was pretty warm for having just run of a minute or so. I started it up again (using the normal wait to start process) and this time watched the amp gauge....it was reading around 10V and clearly was not going through the usual cycle indicating the grid heater was coming on then off...the gauge just stayed down at 10V. I shut it off and started again immediately and the gauge showed 14V. So, it looks like one of the relays is stuck.

I tested both of the relays today (http://dodgeram.org/tech/dsl/troubleshooting/Maniford_htr.htm[/URL]) and they both clicked closed like they're supposed to.

I checked resistance on air intake temp sensor and it seems to be pretty close to where it should be based on the table showing ohms at various temps.

I've done a cold start and it'll stick and then if I shut it off and start again immediately I can bypass the problem. I can also do a cold start and by driving it over about 10 mph I can bypass the problem.

Anybody have any thoughts on where to go next?

UPDATE 5/10. I pulled the leads on each relay independently this morning at 38 degrees and the system functioned properly...cycling on and off after the start. I then tried it with both connected and it also functioned properly (I jus' love problems that fix themselves!). I'll continue to track when it malfunctions and try to isolate the problem to one relay or the other before moving on to the intake air temp sensor or the ecm.

UPDATE 5/11. Cold again here this morning at 29 degrees. I started it up and the system funcitioned properly. I let the truck sit until midday when the ambient temp was 50. I started it and the grid heater stuck on. I'm thinking this suggests the intake temp sensor is bad. I plan to replace it in the next week or so.

UPDATE 5/20/16. Replaced the intake temp sensor and all seems to be functioning correctly now.

 

[The patriot]

If it's warm enough out, you could always unhook it from the drivers side battery + lead. Assuming it's the same as my early 1998.
It's the one with about 10gauge double lead wire.
I usually take mine off in the spring, so I dont even cycle the grids all summer.

 

[BigPapa]

I tested both of the relays today and they both clicked closed like they're supposed to.

I've done a cold start and it'll stick and then if I shut it off and start again immediately I can bypass the problem. I can also do a cold start and by driving it over about 10 mph I can bypass the problem.

This leads me toward a sensor issue, feeding bad or no data to the PCM or, less likely in my opinion, a bad PCM.

If the relays are functioning properly and the PCM is commanding them off above 10mph as it should, the only thing left is the sensor or related wiring.

 

[fest3er]

Disconnect one of the two control leads on each relay. If either relay still comes on, you have a bad relay or two.

The stock relays can *sound* OK (though they always sound anemic). But they have weak springs that often wear out after a couple/three years and no longer hold the contactor off the high-current terminals. If you notice your headlights/dashlights flicker at night when you drive across a rough-ish road but they don't flicker on smooth roads, you probably have bad relays.

After the second set on my '98 failed, I replaced the stock relays with "industry standard" relays. See my solution. 15 years and the Stancor relays are *still* as good as new.

 

[BigPapa]

Just relaying my experience, I'm still running the original '95 relays. 17 years old and 500K+ miles.

 

[GAmes]

My original relay(s) failed when mine was still in warranty. The dealer in Newport News, VA replaced them, then charged my wife for two new batteries because they had boiled over. (I was out of town) I bypassed the PCM and have the ground wires hooked to a toggle switch. That was the last time I let a dealer work on my truck.

 

[Missouri Mule]

You can clean the tip of intake air temp sensor with alcohol.*
It could be the pcm. If it turns out to be pcm you can run a remote switch to relays.8

 

[Missouri Mule]

You clean the iat sensor tip with alcohol.
It could be pcm, lf it is you can run one or two switches to the relays.

 

[The patriot]

This leads me toward a sensor issue, feeding bad or no data to the PCM or, less likely in my opinion, a bad PCM.

If the relays are functioning properly and the PCM is commanding them off above 10mph as it should, the only thing left is the sensor or related wiring.

Mine seem to go off around 18 mph. fwiw....