Fuel Sending Unit/Gauge - SOLVED

[RAMurphy]

Hey all, just recently started experiencing some issues with my fuel gauge readings. A little background, almost 2 years ago I replaced my fuel pump. I replaced it with the A/C Delco. What a pain in the ass dropping the tank and getting the retention ring off and back on. But I got it done. The issue: Randomly the fuel gauge on the dash will go from full to empty and stay there. I will get the low fuel warning indication when this happens. Then after awhile it will move back to full. Now this happens more often when the tank is full. Less often when less then full and almost never when the tank is below a half of tank. Correct me if I'm wrong. I seem to remember that the low fuel warning light is tied to the fuel float sensor. So my assumption is I either have a faulty sensor or problems with the wiring - not the gauge on my dashboard. Thoughts?

 

[Fless]

Agreed. No matter what the gauge needle or stepper motor shows, it has no effect on the Low Fuel light.

You could monitor the fuel level with a scanner that reads that PID to see what the circuit is reporting for fuel level.

 

[89Suburban]

I swore I just read something today about this same phenomenon somewhere on here somewhere.

 

[SilverSport]

I have read and experienced similar issues that were traced to the fuel and float in the tank and each time it has been cleared up by a dose (I double dose) Chevron Techron...

the stepper motor issue would be my first guess and using Chevron Techron Complete Fuel System Cleaner would be something I'd give a shot to next...also use Top Tier fuels when you can

good luck with your Tahoe

Bill

 

[RAMurphy]

Agreed. No matter what the gauge needle or stepper motor shows, it has no effect on the Low Fuel light.

You could monitor the fuel level with a scanner that reads that PID to see what the circuit is reporting for fuel level.

Thank you for the response, sounds like a plan and what I need to do. When it goes back to reading fuel quantity it appears to go back to the correct fuel amount. Sure hope it is a wiring issue, I don't want to drop the tank again and the rest of the work associated with getting the fuel pump unit replaced.

 

[RAMurphy]

I have read and experienced similar issues that were traced to the fuel and float in the tank and each time it has been cleared up by a dose (I double dose) Chevron Techron...

the stepper motor issue would be my first guess and using Chevron Techron Complete Fuel System Cleaner would be something I'd give a shot to next...also use Top Tier fuels when you can

good luck with your Tahoe

Bill

Thank you. I will give the dose of Chevron Techron a shot. I've always used top tier fuels.

 

[strutaeng]

Hey all, just recently started experiencing some issues with my fuel gauge readings. A little background, almost 2 years ago I replaced my fuel pump. I replaced it with the A/C Delco. What a pain in the ass dropping the tank and getting the retention ring off and back on. But I got it done. The issue: Randomly the fuel gauge on the dash will go from full to empty and stay there. I will get the low fuel warning indication when this happens. Then after awhile it will move back to full. Now this happens more often when the tank is full. Less often when less then full and almost never when the tank is below a half of tank. Correct me if I'm wrong. I seem to remember that the low fuel warning light is tied to the fuel float sensor. So my assumption is I either have a faulty sensor or problems with the wiring - not the gauge on my dashboard. Thoughts?

I've got this exact same issue on my 04 project Suburban. In my case, however, I get a code for the auxiliary tank. I don't drive that vehicle. I thought maybe the float had gotten stuck from sitting and I put fuel in it and did a few wot and braking, but didn't issue came back.

I suspect the float/sender...

With my scan tool I can see the voltage of the auxiliary tank kinda fluctuating, it's not a steady voltage.

I just happen to also have a cluster that drains the battery, but I "believe" my guages are all good. I have to fix the cluster for the battery drain issue, but I don't think that's the issue with the intermittent fuel gauge going to zero.

Good luck and keep us posted.

 

[Fless]

the stepper motor issue would be my first guess and using Chevron Techron Complete Fuel System Cleaner would be something I'd give a shot to next...also use Top Tier fuels when you can

The gauge stepper motor DOES NOT AFFECT the Low Fuel light circuit.

 

[RAMurphy]

Thanks all. An update: Ran my scan tool and although the gauge was steady and reading about 3/4 of tank (which is pretty close to accurate based on the amount of miles), I was able to pick up a stored intermittent code of P0463. Seems like I have a fuel sensor problem, although I will do some additional troubleshooting.

 

[RAMurphy]

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.

 

[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).