Gas Gauge from Hell

gmc
1500

#1

I’ve got a 2001 GMC Sierra 1500 with about 80,000 miles and with a gas gauge that is possessed. It sometimes appears to be working normally, but is just as likely to do very weird things, like: When I fill up the car with gas, it will always register empty. And it will stay there until it sees fit to move to full. BUT: if, as I’m traveling down the road, I move the transmission from drive to neutral, the gas gauge will move to full. This also happens arbitrarily between fill-ups, with the gauge sometimes registering empty and sometimes finding some random place around where it should be. Once again, if I put the car in neutral, the gauge will move to its correct position (at least I think it’s the correct position!). I was told my one mechanic that the problem is that the fuel pump is wearing out, and that this problem is not uncommon for the Chevy/GMC trucks. The fuel pump is in the gas tank, I’m told, so to replace the fuel pump is rather expensive: $700./$800. bucks. I would greatly appreciate any help in either confirming this diagnosis or identifying the true cause of my erratic gas gauge. Thanks!


#2

The fuel level sender is the most likely culprit and it’s attached to pump. The way you get them nowadays is the whole module which includes pump. This can be diagnosed before before replacing module, so there should be no need for misdiagnosis. Besides being fuel module it could be wiring, gauge, or powertrain control module. Is this something you are prepared to tackle yourself? If so reply back and let us know. We’ll help you through the steps.


#3

You Should Be Able To Buy Just A Fuel Level Sensor After Diagnosis Indicates It’s Bad.

GM has had several model-years and several makes / models that have in-the-tank fuel sensors (sending units) that are literally eaten up by sulfur in the gasoline.

I replaced one in one of my cars myself and saw what happens. There are tiny little electrical “fingers” on the “wiper” portion of the sensor arm that is connected to the float. It wipes over a part of a small circuit board as the float moves with fuel level and sends a signal indicating the fuel level. Those little metal fingers dissolve and start making poor contact with the circuit board.

The bad news is that after proper diagnosis and confirmation that the sensor is bad, I do believe that the tank has to be lowered and the fuel pump module extracted in order to install the sensor.

The good news is that I believe your vehicle has available just the fuel level sensor as a replacement part from GM and the part is not extremely costly. Some vehicles make it necessary to replace the whole fuel pump module / fuel sensor assembly at a much higher cost.

My GM passenger car had a small access panel in the trunk and I was able to replace the sensor (mine was about $50) myself in my driveway. Anyhow check with your Chevy dealer and / or GMC to check on the sensor availability and price.

Many will tell you that you need to buy the whole fuel pump / fuel sender module, but I don’t think so. The way I understand it is that GM had to replace so many senders under warranty that they made the part available as a separate piece. I bought a GM Part # 1582-4379 from a dealer. It fits trucks, not cars, but I just used the wiper piece and it worked great. A parts guy should be able to tell you if this whole sender unit will fit your module. It should easily snap into and plug into your fuel pump module, once it’s pulled. It was about 50 bucks if I recall.

Get it fixed, but keep the mechanic happy and let your fuel level get pretty low before going for replacement. Otherwise the tank will be heavy and have to be pumped out.

CSA


#4

If your fuel pump was bad, you would have drivability problems. The fuel sending unit could be the problem, but they way you are describing the problem, I’d suspect the body control module. This could get very expensive to fix. Of course it could also be something as simple as a ground wire connection, but that could be costly to find.

My suggestion to you is to reset the trip odometer every time you buy gas and refill based on that odometer.


#5

This is a common problem on GM’s of this vintage. The gauge on my 2000 Blazer quit working nearly 3 years ago. Evidently sulfur in gas builds up on/corrodes the contacts on the fuel level sending unit. Chevron Techron states that it has additives to clean the sending unit. GM also has a fuel cleaner to clean the sensors. I’m pretty sure it’s rebranded Chevron Techron at 3x the price. Since your gauge is working part-time, try the Techron first.

Two bottles of Chevron Techron didn’t help the sending unit on the Blazer, but the truck ran smoother afterwards. I add Chevron Techron or Seafoam to my vehicles once or twice a year anyway.

What I do is fill the tank up completely and keep track of the miles. For example in the summer the Blazer can go 255-270 miles with a ~3 gallon reserve and in the winter 240 miles between fillups.

Ed B.


#6

I’ve Seen This In Action And Although It Does Sound Like A BCM Problem, It Very Well Is Just The Wiper On The Fuel Level Sensor.

I replaced a BCM once (Chrysler) because of a fuel gauge / w/wiper issue and I’ve also replaced a GM sender that had these same symptoms that mmorlock321 describes. Edb1961 is correct. I had the wiper from my sender in my hand and you can clearly see that the sulfur literally dissolves the metal fingers on the sensor’s wiper. This is quite common on Chevy and GMC trucks.

CSA


#7

If testing shows the problem to be with the tank sending unit–which is quite common–the sender is available as a separate unit. Should save you $150 on the parts. However, the labor cost will be the same, as the tank still needs to be removed from the truck to remove the fuel pump module and replace the sender.

Be sure your shop checks fuel pump operation first–and I don’t mean a pressure test, as that’s not really useful. Have them use their labscope and low-amp probe to test the pump rpm, amperage draw, and waveform. An experienced tech can do this in 5 minutes and come to a determination about the “health” of the fuel pump. If it looks less than perfect, just replace the whole assembly rather than have to do the job again in a year.


#8

I purchased my 2001 gmc sierra 1500 extended cab new in july of 2001. I had no problems with the gas gauge until about 80k when I started experiencing the low fuel light would come on even when the gas tank was full to 1/4 tank. When the vehicle had 103,000 mi’s on it I spoke with a local garage who charged me approx $675 to replace the fuel pump. They had to remove the drive shaft, and the gas tank to replace it. Everything was fine for about 20k miles. Now the truck has 123,000 mi’s and the same thing is happening again only much more frequently. I came to this site today to try and find a solution that will disconnect the current fuel pump asssembly and allow an after market fuel pump to be installed outside the fuel tank. Who are the damn engineers that have thought this through? T Bittner BBL CA


#9

I’d Hate To Think You Replaced A Perfectly Good Fuel Pump Module When All You Needed Was A Fuel Sensor Installed On The Old Fuel Pump Module. Many Mechanics Don’t Know It’s Available As An Individual Part.

The damn engineers may not be the ones causing all of your grief. Was an OEM pump installed or an aftermarket one ? Were you having pump problems or just gauge problems ?

CSA


#10

Thanks so much, Pete. I don’t have the skills to do this, so I’ll have to take it to a mechanic. Will the GMC dealership be able to diagnose this? How about a general mechanic who would be a lot less expensive?

Thanks again,

Mark


#11

Thanks so much for your great response. Everyone else who’s responded feels basically the same way, so I think I know what to do.

Best wishes,

Mark


#12

Thanks, Keith. I think I’ll see if I can get it diagnosed, but in the meantime I’m taking your advice and using the trip odometer.

Best wishes,

Mark


#13

Thanks for the quick response. I’m taking your advice and using the trip odometer, but will try at some point to get the problem diagnosed by a qualified mechanic.

Best wishes,

Mark


#14

Thanks for the great advice. I’ll do all of what you recommend.

Best wishes,

Mark


#15

Thanks for your reply. It must have seemed like a good idea at the time…

I guess I’ll try to get it diagnosed by a qualified mechanic.

Best wishes,

Mark


#16

Thanks for the reply. I guess I’ll have the problem diagnosed by a qualified mechanic at some point.

Best wishes,

Mark


#17

Thanks, Keith. I’m taking your advice on using the trip odometer. I’m hoping a qualified mechanic can at some point diagnose the problem.

Best wishes,

Mark