2000 GMC erratic gas gauge

[Wayne02]

2000 GMC Sierra 2500LD new body style, 6L, auto, 4x4, ext cab, 87K miles.

Several years ago while driving on a rough forest service road the gas gauge started acting erratic. The gauge will show fuel in the tank and suddenly drop to completely empty and the low fuel light comes on. Hit another bump and it pops up again to the proper level. Another bump and it drops to empty again.

I have been living with it for the last several years but it seems to be getting much worse very quickly these last couple of months and I should probably fix it I guess.

A scan with the OBDII scanner shows no trouble codes, but my assumption is it's the sender in the tank since the gauge seems to be working. I seem to recall hearing or reading that these trucks may have weak fuel pumps from the factory and are given to failure after some miles are on the rig. Hmm, I wonder if the sending unit is part of the pump assembly?

So my questions are:

- Are there any tests I can or should do to confirm a faulty sender before dropping the tank? Or is it pretty likely it is the sender?

- Are the in-tank fuel pumps on these trucks prone to failure or is my memory off on that?

- If the pump is a weak spot, with 87K on the rig I wonder if I should just go ahead and replace the pump when I replace the sending unit? If so, should I go with an oem pump (assuming it has been improved) or go with an aftermarket pump?

I'm fortunate to have a lift in my shop and a tall transmission jack that I can use to position/hold the tank for removal and installation. Otherwise I might consider cutting an access hole in the bottom of the bed to change the pump rather than go through the hassle of dropping the tank.

Thanks

 

[gunsmith11]

Dont rule out the instrument cluster

 

[MK]

I'm not much up on what GMC is using for senders.
I'd make sure any wires to ground are making good connection.
Almost sounds like it's losing a ground or sumtin..
I'd need to see a manual to guess any farther than that.

 

[2Loud4You]

The fuel pump and sending unit are 1 and they're hella expensive. Sounds like the sending unit has gone haywire on you.

 

[jbouwens]

Howdee,
Pumps fail when they fail, no telling, I have changed them from 60,000 -300,000 miles. If you go in for the sender, change the entire assembly, most aftermarket parts are fine, This should be under 200 bucks- call around, As for testing -if the gauge was at "E" then I would attempt to ground the sending wire at the tank—if the gauge sweeps to full or buries past "E" then that confirms the gauge operation—your gauge works at times- these are the toughest problems to find, there is a remote chance that the cluster is bad but I am betting it is the sender.
As for cutting a hole in the bed----DON"T--- take out all the bolts to the fuel hose holding it to the body (through gas door), take out all bed bolts except the two rear ones-- loosen them about halfway, put a jack/lift under the front of the box (one side or the other ( a 2x4 might gain you enough lift) and lift it like you would a dump bed, you can now get to the top of the tank and remove the fuel sender/pump assembly and replace it. This procedure save a ton of time and you shouldn't have to turn a bolt on the tank. Be careful to lift slowly watching the rear of the bed/bumper joint and look out for anything else like electrical wires from the front to the middle of the bed area. Most of the wiring is in the back of the bed so you should not have to remove/disconnect it. Make sure you securely support the bed while it is up so you don't get a "drop box head" The only trucks that I have run across, with this method not working is the 70s/80s Chevy trucks with the front of the tank under the cab (damn things). Good luck and be careful and take your time if you do it this way you will grin about not having to screw around wrestling with the tank.

 

[feralmerril]

If you find out, let me know as I also have a 2000 sierra 1500 with the exact same problem! I just been setting my trip meter and liveing with it. I think you have to pull the tank to fix it and I am not ready to do that!

 

[sjmjax]

Add me to the list...

I've got a 2001 sierra 1500 and it's been doing that for couple of years now. If I fill it up, it shows empty. Works ok most of the time when around half full but will go to empty seemingly at random moments. Hit a bump or shake the truck and it works again. Maybe I'm due for one of those center fuel tank explosions!

Like Merril, I just set my trip odometer and live with it. Got almost 135K miles on it now. About the only problem I have with the beast.

It's a shame it's my last. Kind of like Chevy/GMC trucks. Have driven them since I was a teenager. But, I have no intention of buying another from Government Motors.

 

[nisamo]

I had a 2000 z71 and when I filled the tank it showed empty but after I drove it a few miles it was like it built up pressure and was accurate. It would also drop to E when ideling thru a fast food line or bank drive thru. Again a few miles steady driving and it got to reading accurate. I lived with mine for about 3 years and then told the buyer how it acted. I always filled up and reset the odometer. I was told sending unit was in the tank and a fairly expensive fix.

 

[feralmerril]

Funny how we all have the same problem! My wife has a 2001 silverado. That one is ok.
Its also the only problem I have had. The horn on hers just quit. However, it works on the alarm system? Go figure! I have been toying with the idea of selling both and buying a new 4wd for probley my last new vehicle, if I can get a new one by a dealer going under cheap. Might turn into a classic!

 

[MKT]

I would imagine that the 2000 and newer Suburbans have a different style tank but prior to my 2004 I've had a 1999 and a 1993. Both the '99 and '93 had erract gas gauges, the '93 was the worst. I'd been told that the tank baffles would come loose and interfer with the float, fix was something like $900. The '99 had a dancing needle, sometime. The rest of the time it just sort of vibrated. The dealer didn't nerrow down the possibilities beyond a bad gauge or a bad sending unit. I opted to live with it until it quit completly.

 

[viking1]

Had the same problem on a car, a 2000 Buick Century. I just learned to live with it and check mileage on each tank. Wasn't worth getting fixed. Gave the car to my daughter and schooled her on how to not run out of gas.

 

[jbouwens]

I would imagine that the 2000 and newer Suburbans have a different style tank but prior to my 2004 I've had a 1999 and a 1993. Both the '99 and '93 had erract gas gauges, the '93 was the worst. I'd been told that the tank baffles would come loose and interfer with the float, fix was something like $900. The '99 had a dancing needle, sometime. The rest of the time it just sort of vibrated. The dealer didn't nerrow down the possibilities beyond a bad gauge or a bad sending unit. I opted to live with it until it quit completly.

I pulled an explorer tank down that had a baffle that had indeed broken loose from the bottom of the tank an broke the support structure for the float and pump, The funny thing (for me anyway) was that the owner dropped the tank, repaired the broken upright with that silly steel stuff, and replaced it only to have it wiped out but the baffle again. I ended up pulling the baffle out of the access hole in the tank in little pieces after I broke it up. I don't remember if the 2000 GMC/Chevy trucks using that type of baffle though.

 

[bobf]

My 2000 GMC occasionaly goes to empty then starts working again.
My neighbor is a mechanic and has fixed several of them. He says some trucks have a problem with the wiring at the tank. If I remember correctly it was a pigtail or extension that went bad, if not that the next step is the pump/sending unit assy. $$$$

Bob

 

[41]

I had a 2000 z71 and when I filled the tank it showed empty but after I drove it a few miles it was like it built up pressure and was accurate. It would also drop to E when ideling thru a fast food line or bank drive thru. Again a few miles steady driving and it got to reading accurate. I lived with mine for about 3 years and then told the buyer how it acted. I always filled up and reset the odometer. I was told sending unit was in the tank and a fairly expensive fix.

While idling...your voltage drops because the alternator is not turning fast enough so the battery supplies the voltage. This is a sign of resistance in the wires so you have a bad connection.

Not sure your year model has a separate ground wire instead of using the frame. I would run a separate ground wire from the tank area to the dash panel ground.

The best way to replace the fuel pump and sending unit is to pull the bed. Jack up the rear and pull the wheels off to give clearance when removing the bed. There are only 6 or 8 screws that hold the bed on.

 

[Wayne02]

Thanks very much for the replies so far, once again this forum is such a great resource with knowledgeable folks on all kinds of subjects.

I didn't mention it in the original post but my truck will drop to empty while at idle as well like some others have mentioned. However, it will also do this on a frequent basis while driving down the freeway and then eventually pop back to the proper reading. It seems like it is taking longer and longer for it to recover these days though, and then it is only good for a couple of minutes before it cuts out and goes empty again.

 

[Spotteddog]

Late model (EFI) use a combo pump/sender. Lousy ground or signal leads can cause your issue. But you very nearly have to drop the tank to get to them to verify. It's not uncommon for float set up's (which are actually a variable resistor hooked to a float) to develop so called dead spots in the resistor. To determine if it's the sender you very nearly have to drop the tank as well. No quick and dirty, unfortunately?

 

[fldigger]

My 2000 Chevy Silverado does the same thing. I recall hearing from the local mechanic, that Chevy put out a service bulletin asking that the wiring harness connector at the tank be replaced if you did any work on the gas tank. If that's true, the folks mentioning the grounding issues are probably dead on.
Does anyone else have their ABS and Brake lights come on randomly and stay on? Mine do that off and on. I never know when it will happen. Comes and goes of it's own accord. I have 147,000 on the truck and this about the only problem I have had with it.

 

[Vulcan Bob]

Could be sulpher build up on the electrical contacts on the sender unit, this will isolate the contacts intrermitantly and show an empty condition. Try a fuel cleaner with techron. This will remove the sulpher build up and restore proper function. Give her a shock dose and run the tank out. Had a lot of trouble with a fleet of Ford Crown Vic's. with this and it worked.

 

[GaryDean]

I am a moderator on a GM truck forum and I see people with this problem all the time. The trucks of that era have a gauge cluster problem and GM usually fixes them for free under a silent recall. Contact your dealer to see if you qualify.

 

[Spotteddog]

Thanks Gary!
Don't you just LOVE those "silent" campaign's!