Fuel Level Sensor Issue

[Ian Mills]

So my gas gauge intermittently reads 0 and the low fuel light comes on. However, about 75% of the time it gives a proper reading. It throws code P0463 every time the gauge drops off. 

 

Is there anything I should try before servicing/replacing the fuel sending unit in the tank?

[Mr. Z71]

There is a possibility that it is the fuel gauge. GM had problems with the stepper motors on the tach, speedo, and gauges resulting in false readings. Sorry I can't provide more info or assistance.

 

[davester]

given that the gauge mostly works, it's unlikely to be the stepper motor, other than possibly a bad solder joint on it.  Intermittent problems like this could be the gauge, or could be a wiring problem.

[Ian Mills]

Well I have to say Im leaning away from the gauge. Partly because of the DTC. Would that get thrown if it was just the gauge?

 

Also, I had the cluster rebuilt by Circuit Board Medics about a month ago and they advertise that they replace all the steppers. It's possible though I suppose. How would I test for that?

[davester]

If I were doing it, I would use a tool to display the fuel level in the BCM, and then drive around and see what the bcm reads when the fuel level drops to zero.  If the bcm indicates the fuel level is zero, then the problem is between the bcm and the fuel level sender (including the sender),if it reads the same level, then problem is between the bcm and the IP.

[Ian Mills]

That's a good thought. I don't have a tool that will do that on hand. Would it throw the code "Fuel level senser voltage high" if the issue was between the computer and the gauge? It seems like that would be more along the lines of "cluster circuit something"

 

UPDATE:

I was driving today and noticed a very interesting pattern. The issue only pops up when the truck has been at idle (both drive or park, I checked) for at least a minute. Like at a long stop light or warming the truck up because it was cold this morning. As soon as I put it in drive and move 2 feet the gauge pops right back up where it's supposed to be. I came to a stop three times and waited and the issue popped up all three times after about 1 minute. I tried revving it in park to see if it was rpm/voltage dependent and that didn't fix it. My next step (later today) will be to stop on a hill, wait for the gauge to go to zero and then coast away in neutral and see if the movement is what causes the problem to be fixed.

[Ian Mills]

Any movement at all causes the gauge to pop back up to where it should be. It seems like the fuel sloshing in the tank causes the sensor to make a connection.

[Ian Mills]

RESOLUTION: The sensor in the tank had corroded. I could have just replaced that but I went with a new Delphi pump assembly so I wouldn't have to open up the tank again soon (hopefully)

[txab]

You did the right thing by replacing the entire assembly

[Ian Mills]

16 minutes ago, txab said:

You did the right thing by replacing the entire assembly

Yeah, with 167,*** miles I figured the original pump was on borrowed time anyways

Edited January 21, 2021 by Ian Mills

[kickass audio]

as you found out the stepper motor won't set a CEL for a broken tooth inside the motor. My fiance had the fuel level sensor on her old car do the same thing except it would trigger a CEL at random but typically whenever she filled up the gas tank past 3/4 of a tank and start to use up the gas it would make the fuel gauge go to a full tank of gas and then to empty and set the alert for running out of fuel and then go back to normal for the actual gas in the tank.

 

I pulled the pump out of her gas tank since it was super easy to do without dropping the tank and I had found that the little contact pads where the level sensor rides on and produces varying levels of resistance had a small burn trace on the pad. I had tried to use some contact cleaner for the contacts and clean the graphite contact and it didn't help for more than a few days.