Thought I'd jump in here and provide some info. You have 2 grid heaters that are controlled by 2 relays. The two positive cables coming from the battery connect to one stud on each relay. The other thick black cable goes from the relay to the grid heater. The battery cables should have constant battery voltage. The cables going to the grid heater should have battery voltage only when the relay is activated. The relay is activated by the PCM depending on intake air temperature.

When the relay is activated, the cable from the battery connects, thru the relay, to the cable going to the grid heater so there should be voltage on each cable stud during the heater on cycle.

Each relay also has 2 thin wires which are the trigger wires. The lt green/blk are the battery feed wires and are fed from fuse #9. The yellow/blk and orange/blk go to the PCM and are used by the PCM to ground the circuit and turn on the relay. You should have battery voltage on the pin for the green wire.


Check all this out and turn on ignition and test for voltage going to the grid heater on each relay.

There is a test for the relay if you suspect a relay is not working.

 

hello et ran
ok the irst thing that i will check is the #9 fuse tomorrow morn. but just for giggles, what is the test for the soleniods?. cuz it was 36 deg out when i left work tonight and it did not come on again!!!!. so if i read and understand u correctly the grn/blk wires are batt feed so they are hot with the key one and cold out--- right -- or does the engine need to be running?? yel/blk & org/ blk are ground for the pcm--correct???
grn wire should be hot with the key?? not important that it does not work but i like my stuf to work if it is there---just the way i am-- sorry.. i have one very stupid ??? or u what the heck is the PCM lol? thanks mike

 

No need to check that fuse. It also feeds the fuel shutdown solenoid hold coil. Since you are not having problems with the fuel solenoid, the fuse is good.

The green wires have battery power anytime the ignition switch is on or in start regardless of temperature. The yellow and orange wires are used by the PCM, computer: Powertrain Control Module, to ground the relay activation circuit to turn the relay on and thus turn on the grid heaters.

The way the system works is, power for the grid heater comes from the 2 cables from the battery. When you turn the key to on or start power goes to the green wires. The PCM then grounds the yellow and orange wires to turn on the relay. With the relay on, the cables from the battery connect to the cables going to the grid heater and the heater turns on.

I will post the relay test later tonight.

 

ok thanks ill look for it lator

 

ok the two soleniods on the fender, test meter grnd lead to batt, the two big wires atop each sol. one is grnd and one is hot, engine running, all four small wires, yel/blk,org/blk, and both green(mine are blue) are all hot, if i grnd (to chassis) either the yel/blk--or the org/blk, heater comes on but it stays on and does not cycle,until i remove the grnd to chassis. so is it a soleniod or a computer problem??. now i say the heater comes on only cuz the volt meter (in cab) drops to eight volts when i grnd to chassis, did not leave it grounded for to long cuz i dont want to cause any problems, i did leave it grounded long enough for it to cycle but it did not cycle so i removed the grnd to chassis.thanks mike

 

Ok, I am trying to understand what you are saying regarding your test.
What I understand is that on the two big wires you have one that tests hot and the other tests to ground. If this is correct then the tests you did are correct. With the relay off, you would have the battery cable hot and the grid cable would test to ground. With the relay on, the battery cable would connect to the grid cable to ground to complete the electrical circuit. With the relay on, you would have voltage on both cables.


On the small wires when you test for voltage, you would read voltage on both pin connections. Power comes from the fuse to the blue wire connection, thru the relay coil to the other wire that goes to the PCM. So yes, those wires would show voltage up to the PCM.

What apparently is not happening is the PCM is not grounding the circuit for the grid heater to turn on. When you ground the yel/blk and org/blk the relay activated and the grid heater turned on until you released the ground. What you did is you became the PCM by grounding the circuit.

I would say you have a computer, PCM, problem. But, it may be related to the intake air temperature sensor. I will have to read some on how the sensor works, see if there is any info there that will help.

Right now I would say the PCM is not controlling the grid heaters. The relays are working because you ground the trigger wire and the grid heaters turned on. The problem goes back to the PCM.

One more test you can do is ground that circuit again and test for voltage on the cable that goes to the grid heater. You should have voltage.

Are you having a hard time starting cold. You may be able to rig it temporarily to get the grids going for starting.

 

no it is starting fine, i just like it to work like it should,, one wire at the grid is hot and one is not, so i will ground the soleniod again and see if both get hot when i do that, i am sure it will cuz the grid turns on when i do that. i know it wont hurt anything for the grid not to come on , i just like it to work like it should. i was told the pcm is located on the right inner fender, i can not locate the ecm(pcm ) as u call it . is it somewhere else. 93 1st gen 5.9 12v d350

 

anyway to bypass the air temp sensor to see if that is the problem??

 

ok grnd the system and everything at the grid gets hot, mabe i excited the system cuz it worked this morning when i started the truck

 

Check to see if you have any corrosion on the relay terminals. Remove the negative battery cable from both batteries. Disconnect the wiring to the relay and clean the terminal posts and wire terminals. See if that helps.

My manual only goes to 94 so not sure where the computer is mounted. I will check another source and see if I can get the info.

Haven't had a chance to check on that air temp sensor. Will let you know.