Engine/Transmission (1998.5 - 2002) No power to grid heater

[farkum]

This question has been asked a thousand times and I have read half the responses. However I still cant figure out what is wrong with this truck. My friend has an 01 CTD and we live in Bozeman, MT. The temp recently dropped and now his truck is really hard to start when cold. First thing I did was pull out the test light and check for power to the grid heater, nothing. Then I tested power to the relays, nothing. I have looked through both fuse compartments to no avail. Is there a fusible link somewhere else that I can check, this is bugging me. The relays are fine, if I use a jumper to give them power they both will switch and then the grid heaters come on.

 

[JFaughn]

Not sure about your yr mod , but most have a fuseable link at the battery on the drivers side , that go down to the relays on the fender well , below & behind the battery , so the connections at batt. or the fuessable links [ if the links are bad then there probubly is a high res. on that circut ] .

 

[B.G. Smith]

A schematic I have shows the hot side of the relay coils comes from a splice that also feeds the shutdown relay and the fuel heater. That should be a 20 ga. wire, light green with a black tracer. The other side of the relay has a red with black tracer on one and a orange with black tracer on the other and goes to the PCM which controls when they come on. bg

 

[farkum]

As far as I can tell the light green wire with black tracer is supposed to be the ground and the other two go to the PCM and control when the grid heater is on. Is this correct? If not then we have issues because the light green wire with black tracer is definitely a good ground and I have nothing at either of the other two wires for negative or positive, even when the wait to start light is on. This would lead me to think that the PCM isn't ever engaging the grid heater. Is there a intake temp sensor on this truck? If so is it possible that its always showing hot and the PCM doesn't think it needs a grid heater ever? Any other sensors that may stop the PCM from turning on the grid heater? Tomorrow I am going to try to manual power the relay to make sure they both work and the grid heater still works. Don't worry I will disconnect the wires going to the PCM first, don't want to risk frying that. If anyone can think of anything else to check please let me know. Its getting cold again and his truck does not like starting right now. Almost had to get the hair dryer out last night.

 

[B.G. Smith]

After looking at the schematic again, I see that the circuit that has the light green wire and black tracer has a "G" designation, for ground I assume. I am definitely challenged when it comes to trying to read these. The temperature sensor that triggers the heaters is the IAT, intake air temperature sensor and is mounted in the intake manifold toward the rear of the engine. bg

 

[Bodie]

After looking at the schematic again, I see that the circuit that has the light green wire and black tracer has a "G" designation, for ground I assume. I am definitely challenged when it comes to trying to read these. The temperature sensor that triggers the heaters is the IAT, intake air temperature sensor and is mounted in the intake manifold toward the rear of the engine. bg

Can you post the schematic?

 

[B.G. Smith]

I'm sorry, I don't have the equipment or expertise to send. I could mail a copy to you if that would help. bg

 

[mhenon]

I think this will work on an '01... turn the key on and off 3 times. . leaving it on the third time. Your odometer will now be a code reader.

Tell us what codes are showing and maybe we can run down the problem. I believe the grids are supposed to come on anytime the temperature is under 70 degrees (or some figure). Sounds like the PCM isn't getting the message.

Mike

 

[JFaughn]

The computor almost never turns any thing on directly , they need a sensor to tell the what is going on , then they are not rated for heavy loads , the basics of working on computor controled engs is a pyramid , sensors one point , progam 2nd point , and actuators [ relays, solinoids ect. ] the 3rd point .
The conputors control dievices through grounds , so for the heaters it works like this , the sensor says its cold [ how cold is the progam ] the computor grounds the wire to the relay , closing the points [ + ] sending power to the heaters .
Most offen the prolums are connections , and on this problum for these trucks the comin is the fusable links at the battery + and the points in the relay .
Hope this helps .

 

[farkum]

okay guys I replaced the IAT sensor and still nothing. However the resistance on it is way off what the specs for it are so I am sure it will have the gas mileage. Is there any chance someone can get me a copy of the wiring schematics for this truck. Also any other sensors that could be off telling the computer to not run the grid heater? There has to be at least four relays for this and I have only been able to officially test the two bigger ones. There is no way the computer is controlling those, there have to be two smaller ones somewhere that I haven't tested. Anyone know where to find these? I looked in the fuse box and the closest thing I found to grid heater was Fuel Heater Relay.

 

[farkum]

Tried getting codes and this is what I got



p ecu

------

p1693

-----

p done

p ecu

------

p 0382

------

p done

 

[farkum]

I looked up those codes and I am definitely going to need a schematic for this. I am sure with that and patience I will be able to find the problem.

 

[Bulldog80]

farkum, Did you find any other relays? I'm having the same problem. I've got power to the two big relays on the fender but they're not triggering. I've even replaced them thinking it was the relays themselves. Still no power.