Aux. Fuel Cell Issue

[TexasCanesFan]

I thought I had seen a post regarding this, but I can't seem to find it. I know a few of you have auxilliary fuel cells and somebody was having the same issue. I have a 100 gallon fuel cell in the bed that is hooked directly into the fuel line utilizing a 6 port valve. The equipment is orginally from Auxilliary Truck Accessories, formerly of Garland, but lastest install was done by one of their old technicians. It has a switch in the cab for changing from main to aux. and both tanks read on the factory gauge. The truck is either running off the main tank and reading its sending unit or running off the aux. and reading its sending unit. No kind of transfer from aux. to main at all.

I keep getting the P604 error code, i think that is the code, for the fuel level sensor. Basically, the truck does not understand how we have went 800 miles on half a tank of diesel.

Anybody got a good remedy for this? I had thought of using a seperate fuel gauge for the aux. tank, but then the factory gauge will always read the main tank and will not change when running off the aux. tank. I would think this would create the same problem and get the same error code.

Any suggestions??

 

[Kleetus]

Are you sure that's what P604 means? I'm thinking that depending how that switch operates, it might either short or completely open the contacts before connecting up to the other tank. This is make before break or break before make.

Maybe the computer is seeing that temporary and quick disconnection and is reading that as a fault. The reason I think this, is the fuel gauge is washed through the computer, as a continuous linear average. They did this to keep the needle from bouncing around on slosh in the tank. That's why if you fill the truck up while it's still running the gauge takes time to read full. But if you cycle the key, the computer picks up the reset, and then takes a tank reading making the assumption that it's not sloshing too bad, and displays some value of fuel remaining. Make sense? So, it the computer sees open circuit for a moment, and it's not supposed to ever see that, it will probably bitch about it.

Try doing your tank switch, and cycle the key off and on and see if that doesn't make the reading change faster, and make this P604 go away.

 

[TexasCanesFan]

I thought that was the number of the error code, but I may be wrong. I just had it hooked up this morning and the check engine light turned off. But I do know it was the fuel level malfunction error. The gauge has been reading correctly the whole time, with no loss of power or anything like that.

Actually I had not flipped the switch when the light came on. I had run about 700 miles on the aux. tank when it came on. This is the 2nd time and it has come on the same way both times. The light will stay lit when the truck is started, not while the truck is running down the road. When it came on this time, the switch had not been flipped in the 2 weeks, since I filled up the truck.

Maybe that will make more sense!!!!

 

[TexasCanesFan]

Just called my buddy back and the code is actually P0460, I was close!! It is a fuel level sensor malfunction.

 

[Kleetus]

But it only throws the code when you're running on the aux tank, right? Maybe the resistance of the sender is off, or there is a high resistance short to ground or ground loop that the ECM doesn't like.