NEED HELP GMC Sierra Driver's Information Center

[JRW81]

Greetings: The truck is a 2005 GMC Sierra 2500 HD diesel.
The fuel gauge is reading off scale, so the stepper motor is probably inoperative. I had the shop check the tank sending unit and they said it seemed to be operating and they estimated from their reading that the tank was at about 3/4 full. That would also have been my estimate judging from the time I filled it up.
The Drivers Information Center presents a Range message (miles to go) of only 58 miles and a similarly low reading even after fill up.
The question is:
From where does the DIC get the information to present a computed "miles to go?" Is it from the tank sending unit, or the Gauge or from somewhere else?
Thanks for your help.

 

[azswiss]

Just a guess, but I would suspect the PCM calculates a range value based on known tank capacity, fuel level (remaining), and most current MPG. When you say the fuel gauge is off the scale, which side, full or empty? How did the shop check the fuel level reading, scan tool or direct measurement?

 

[Mooseman]

It calculates it according to your fuel level and the average MPG it is calculating from the instant MPG over time. You can reset it and it will recalculate it once you've driven it a while.

 

[TJBaker57]

fuel gauge is reading off scale, so the stepper motor is probably inoperative

A stepper motor issue should not cause the "miles to go" to be incorrect.

 

[JRW81]

Just a guess, but I would suspect the PCM calculates a range value based on known tank capacity, fuel level (remaining), and most current MPG. When you say the fuel gauge is off the scale, which side, full or empty? How did the shop check the fuel level reading, scan tool or direct measurement?

Thank you for your thoughts. When the ignition is turned on the fuel gauge stepper motor randomly flips the pointer to anywhere between off scale full to off scale empty. I'm not sure what method the shop used to determine that the tank sending unit was working properly, or how they estimated the fuel in the tank. But this place has been around since 1984 and probably has about every piece of test equipment I could imagine. Since I will get the instrument cluster rebuilt for the stepper motor issues, I was just wondering if the Driver's Information Center problem would be resolved following the stepper motor replacement. Thanks again for your input.

 

[azswiss]

Sounds like you have another issue in addition to the erratic stepper. As @TJBaker57 points out above:

A stepper motor issue should not cause the "miles to go" to be incorrect.

The PCM may be getting an incorrect reading so the next step is to compare the fuel level signal at the PCM connection to the signal right at the level sensor connection at the tank. Also, check the connectors to make sure there is no junk/corrosion.

 

[TJBaker57]

probably has about every piece of test equipment I could imagine

Reading fuel level doesn't require any fancy hardware. A $20 Bluetooth OBDII adapter is capable. The data is likely available with a request for standard PID $2F, or the usual GM PID $1155, or maybe even a Class B Data message to the "Fuel System".

Of course one would need to know how to do that !

 

[Mooseman]

I would definitely get fuel level data directly using a capable scanner or @TJBaker57 's method, which is cheaper.