Grid heater controller

[radixr]

Hey, guys. I got a problem. My grid heater cycles whenever I start my engine; hot, cold, or warm. Thinking back, the operation of my grid heater has always been a bit erratic. Sometimes it would cycle when the engine was warm and it never had more that two modes of operation -- full cycle or none even though the shop manual describes 4 different modes of operation. The "wait to start" light either went out right away or stayed on about the 30 second max.

There is another strange symptom -- my 4-wheel drive dash indicator light stays on all the time. I pulled the plug on the switch and it is still on. These two problems showed up in a span of less than one week. Do we have a central computer like those overvalved engines? What does control the grid heater cycle (besides the input from the intake manifold temp. sensor)?
Help! I'm pulling what little hair I have left out by it's roots trying to figure this out.

Thanks, Dave

 

[BTanzini]

Radixr,the heaters are all controlled from the PCM(Power Control Module)through the temperture sensor which sends a signal to the PCM. It is located on the passengers side mounted to the fire wall,engine side, on isolater pads so it does not come in contact with the vehecle ground. Hope this answers part of your question.

 

[Missouri Mule]

radixr,
When your "wait to start" light stays on his your volts doping down to 8 on the voltemeter(pre cycle) 10 to 11 (post cycle)?
If it is check out sensor then heater relays, connections and wires. I doubt that computer is messing up.
I thought I read in book that the sensor activates the light directly but could be wrong(it mite send message to computer first.
Which switch did you unplug?(Trying to eliminate light).
When light is on is your front axle engaged?
I would have to look at manual to see which one activates light( axle switch or switch in transfer case).
If not a switch gone bad, we are back to shorted wire,connection. As I recall the computer has nothing to do with 4 wheel drive operation.
Will look thru manaul tomorow and try to find out something. But I tink both problems is short somewhere or I should say grounding out. I believe that the computer recieves a singal by change of resistance in the sensor I think this is what turns on the light also.

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Bill Thomas
Missouri Mule - 96 Wht 4X4 ST CC,5 spd, 3. 54, 8 ft bed, 1 ft high cheater boards.
99 Freightliner bl/wht FL60 ISB-5. 9 24v,215 hp,520 tq,6 spd, 3. 59 nsr,16 ft box, 19. 5 tires,Wt/gvw 11,000/23000

 

[radixr]

Bill T,
When my "wait to start" light is on the voltage does drop down. I ordered a DMM to check the resistance of the temp. sensor.

I unplugged the switch on the back of the front differential. The light is on whether or not I'm in 4-wheel drive. I didn't know there was a switch in the transfer case.

I thought the 2 problems might be connected because they showed up at the same time. Thanks for your help! #ad


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1996 Dodge 2500 4X4 SC, SLT, Cummins 12V, 5-spd. , JRE 4" exhaust (my kitty ran away into the woods and the muffler fell off!), TST 280 HP/685 Ft-Lb Uprate Kit, AFC Spring Kit, Horton Fan Clutch, Jacobs/Ram Exhaust Brake, MagHytec Differential Cover, Prime-Loc, Rancho RS9000 Shocks, Combo Gauge, K&N Air Filter, Brite-Box, Geno's finger-touch oil pan drain plug, Optima Yellow Tops, no turbo silencer ring, full-time fog lights.

 

[illflem]

Dave,the sender for the 4 WD light is on top of the pass side front axle. Try unpluging it, if goes off the problem is with the switch or maybe vacuum and you are stuck in 4WD. If it stays on you've got me.

 

[Missouri Mule]

radixr,
Got the manual out today switch is located at front axle none in tranfer case. There is a switch but not for the light.
When you unplugged the switch did your light go off?
If not look for bad connector or wire grounding out. 4 wheel drive light is turned on by the switch grounding. The Light has power all the time(if ignition switch is in run posittion).
If it went off more than likely switch is bad or your always in 4wd.
Hope fully just switch or bad connector/wire but if stuck in 4wd vacuum leak or pinched hose.
Also stuck axle could be caused by front axle dis/connect motor could of went bad.
I've seen trouble shooting section on this but have to roam thru manual to find it.

On heaters sensor most likely to be the problem but check out the relays/connectors/wiring.
Book says that ground is provided by PCM (computer)to coil. You also have power being supplied thru the PDC to these coils. The power is provided thru same wiring but ground is supplied on diferent wires(circuits).
One of the small wires going into relay must be ground wire.

[This message has been edited by Missouri Mule (edited 01-30-2001). ]