Fuel Sending Unit/Gauge - SOLVED

[strutaeng]

One of the possible failure mode of this code is "Malfunctions within the PCM". I'm not experiencing any other issues so I assume this is not a likely source of the issue. Thoughts? I guess I will need to drop the tank to complete verify wiring issues. My gut, tells me this is a sending unit issue.

You could back probe the wire for the fuel sender at the PCM, and monitor the voltage.

I came across a thread on performancetruck.net of a guy that posted what voltages should be for a given fuel tank level. I would post it, but I don't remember how I even came across that post honestly. I vaguely remember the thread was about some changes GM had done for different years on the impedence values for the senders? IIRC?

 

[Fless]

I'd say pull the two connectors on the PCM and check for cleanliness and pin fitment.

Also see this thread that seems to indicate that there may have been an updated "calibration" for the later models (the thread is for a 2004) but something like that might also apply to yours. If you have a scanner that reads the calibration IDs you may be able to see if a newer one is available.

2004 Suburban PCM/Fuel Level Problem

Hey Y'all. My 04 Suburban is driving me nuts. I'm not sure where to go from here. Heres what's been done. New rebuilt cluster, new Delphi fuel pump, used PCM matching numbers and from a truck with matching RPO codes. I had a junkyard PCM I installed on Saturday, then we installed a new...

www.tahoeyukonforum.com

 

[iamdub]

You could back probe the wire for the fuel sender at the PCM, and monitor the voltage.

I came across a thread on performancetruck.net of a guy that posted what voltages should be for a given fuel tank level. I would post it, but I don't remember how I even came across that post honestly. I vaguely remember the thread was about some changes GM had done for different years on the impedence values for the senders? IIRC?

The early GMT800 ('99-'02) was 250Ω full, 40Ω empty. The switch to CAN bus in '03 and on through the GMT900 had the impedance scale reversed to 40Ω full, 250Ω empty.

 

[iamdub]

James @swathdiver shared this with me a few years ago when I was replacing my pump module and discovered the failed level sensor:





Keep in mind that this is for a GMT900. Just invert the "E", "1/4", "1/2", "3/4", "F" and "Low Fuel Indicator" gradients for your pre-'03 model.

 

[RAMurphy]

Wow, great information. I will most definitely look and check on these numbers. Thanks again everyone.

 

[swathdiver]

From the shop manual:

 

[RAMurphy]

James @swathdiver shared this with me a few years ago when I was replacing my pump module and discovered the failed level sensor:

View attachment 421727



Keep in mind that this is for a GMT900. Just invert the "E", "1/4", "1/2", "3/4", "F" and "Low Fuel Indicator" gradients for your pre-'03 model.

This is great. Thank you.

 

[RAMurphy]

From the shop manual:
View attachment 421739

Great information. Thank you.

 

[RAMurphy]

T0ok my scanner out to the Tahoe and did a little trouble shooting. I took numerous screen shots and I will post data a little later after my wife and go out for a drink and dinner. First - the gauge would not drop to empty during this test (bummer). But it did fluctuate from just over a half a tank to nearly a full tank. Third - which is interesting, it stated my fuel capacity was 21.6 gallons. Which is not accurate. I've added more than that during a couple of fill ups. More to follow.

 

[RAMurphy]

Some random and crazy numbers/readings. So like I said in my last post, for whatever reason my scan tool reads that the fuel tank capacity is 21.6 gallons, i know that is incorrect. When my gauge indicated full the volts were 2.90 and the indications for fuel level remaining 21.6 gallons. When the gauge indicated slightly less than full (between 3/4 full and full) I had 1.84 volts and 17.4 gallons remaining. When gauge indicated slightly less than 3/4 tank, I had 1.92 volts and 15.1 gallons remaining. Closer to half a tank - 2.02 volts and 12.9 gallons remaining (at 60% fuel tank remaining).