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!

 

[wsl1971]

I just so happen to have my 98 blazer in the shop today. My fuel gauge was doing the same thing and finally yesterday the fuel pump went. My mechanic told me it was the sending unit making the gauge act like that. So $900.00 later i have a new fuel pump and no crazy fuel gauge. I say keep good records of your fuel and miles and just prolong the agony until the pump dies.

good luck
bill

 

[bricker]

fuel gauge

I have a 2005 Envoy with the same problem. Techron brings the needle up to 1/8 tank even when full. Then it registers empty the next day. Cryin shame they can't get it right after all these years!

 

[Wayne02]

Some pricing investigation on the parts (I'll do the install myself) reveals the least expensive to be ebay for an OEM replacement for $180. Comes with pump, strainers, level sensor, tank seal / o-ring. Plus $13 at napa for the wiring harness that is recommended to be replaced at the same time.

Shucks, Napa and GM parts direct have the oem replacements for $333-$352 or so.

Shucks also has a Carter aftermarket kit with harness for $274.

All of these only had a one year warranty though. I did not see any (including the $500+ Bosch units) that had more than a one year warranty.


Good call on removing the bed for the install. I looked at that today and it certainly seems to be the most expedient method. Looks to me like the bed just needs to be walked back a couple feet and may be able to be set/rested on the rear tires. However, I don't know how much that short bed weighs but I suspect it is more than just my son and I can handle. I think I can back the truck under the hoist arms, sling the bed from the tie-down points in the four corners and use the hoist to lift the bed off the chassis. It will be nice not having to mess with draining the fuel, tank straps and hose routing.

 

[bayfisher]

You originally said that you have a lift and a tall trans jack in your shop.

I drop tanks all the time. All you have to do is, raise the truck,put your trans jack under the center of the tank, loosen the 2 hose clamps on the fill and vent tube, pull the driveshaft(gives me room to get a stool to stand on), Remove the two bolts holding the straps that hold the tank to the body, and slowly lower the jack.

You can lower the tank to the point where you can remove the pump assy from the tank without fully removing it. Just make sure you have the tools to disconnect the fuel lines from the pump assy.

The harness problems others have spoke of was if your pump has the flat straight across plug, replacement pumps come with a more squared plug which requires cutting the old harness and wiring the new squared harness to match the new pump assy.

One last word of advice, DON'T go with an airtex or master replacement pump. Put an AC/DELCO in and forget your problems for years. Or you could go cheap. But how many times do you want to change out that pump just because they offer a lifetime gauranty(SP?) Thats why i put ac/delco in my 98 Z71, 6 years and still going strong.

 

[USAF385]

I had something like this happen once. At first there would be small movements of the needle. Eventually they got more and more extreme. It would sink all the down to empty and then jump to full. The entire time I'd be driving it would be doing this. Finally it "snapped" and stuck on way past full. The car ran fine the entire time, and ran for another 3 years. I never bothered having it fixed or finding out what it was... my trip odometer let me know when it was time for gas.

 

[Class III]

I had the same problem on an '88 K-5 Blazer, '93 1500 4x4 and an '02 2500HD 4x4. Loose ground wire on the '93, easy fix. The Blazer and the 2500HD both had a broken baffle in the tank. The spot welds that hold the baffle in place break and the baffle slides around in the tank causing the guage to go crazy at times. Replaced the tank on both the '88 and the '02 with aftermaket tanks and the problem went away. On the Blazer I went with a high capacity poly tank (45 gal). It hung down about 4" lower than the stock tank. Only drawback to the poly tank is that it is more suseptable to puncture than a metal tank. I fabricated a skid plate for it using corregated steel and angle steel and bolted it to the frame. With the extra 14 gal of gas in the tank it was nice being able to fill up every other day. That beast got 12 MPG in town an 14 HWY.

Class III

 

[2Loud4You]

Wayne, be careful using some cheap ebay part. If it doesn't work then you have to do it all over again it might be a pain to return for a working one. I say spend the money and get one from a store near you. Sometimes peace of mind is worth more money. I've done enough to know that sometimes brand new pumps go out.

 

[1968hawkeye]

I have a 2005 Envoy with the same problem. Techron brings the needle up to 1/8 tank even when full. Then it registers empty the next day. Cryin shame they can't get it right after all these years!

I had a similar problem last Christmas with my 2006 Envoy. We were on our way to OK City to visit our son and stopped for gas somewhere on I-40 in TN. Filled up, started the Envoy and the gas gauge was on E and the little yellow light was on. Well, I knew I had gas so we hit I-40 again, as we drove the gauge gradually worked its way to to what seemed like an accurate reading. This didn't go away. When we got back to NC took it in and they replaced the sending unit. Thank goodness, it was still under warranty.

Hawkeye

 

[41]

Good call on removing the bed for the install. I looked at that today and it certainly seems to be the most expedient method. Looks to me like the bed just needs to be walked back a couple feet and may be able to be set/rested on the rear tires. However, I don't know how much that short bed weighs but I suspect it is more than just my son and I can handle. I think I can back the truck under the hoist arms, sling the bed from the tie-down points in the four corners and use the hoist to lift the bed off the chassis. It will be nice not having to mess with draining the fuel, tank straps and hose routing.

Mine is a 1990 with a short bed. I used the mail man to help me lift it off and set it in the yard. Not sure you can slide it back because of the bumper.

It is so much easier working from the top versus dropping the tank. I did a search of the message boards and that was the preferred way to do the job.

I only replaced the fuel pump and it was about $70 at Advanced Auto Parts.

My fuel pump got weak because the fuel filter was not changed as often as required. Overall it was an easy job.

41