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Gas Tank Please help!

I have a Chevy 2006 Malibu LT V6 and when i first got the car a year ago I had no problems. After a few months, I would fill up the tank up completely and then drive it around and stop at a stop light. The gas meter would drop from Full to Empty with the light coming on then reset itself. It happened sparingly so I thought nothing of it. Now just a few days ago I filled the tank up and now the gauge is staying at Full when I know for a fact that I do not have a full tank. Whenever I turn on the car, the gas gauge needle jumps from full to empty to half to full to quarter until ending at full. Lately, I’ve been trying to go off the fuel mileage on my radio but with that resetting to what my fuel gauge says I’m getting fearful of running out of gas. Any help would be greatly appreciated! Thank, Ally.

There is a sending unit inside your fuel tank that sends a signal to the dashboard gauge. The problem could be in either unit or the wiring between the two…In todays world, most mechanics will first replace the inside the fuel tank sending unit and see if that fixes it…If not, they will replace the instrument cluster and hope that fixes it. You get to pay for it all whether it gets fixed or not…80% of the time, it’s the sending unit in the tank. The tank must be removed to replace the sender…$$$$$$. Or just write your mileage down and fill up every 300 miles or so…

I gotta agree with Caddyman. You likely have a defective sending unit in the gas tank, and replacing it will cost you big bucks. It will cost you nothing to leave your car alone and fill up according to your written record of miles traveled.

You can go to an auto parts store and ask for a ‘mileage minder’. It’s a little plastic gadget that sticks anywhere on your dash. You turn the little wheels to set the mileage display to whatever you want, such as 300 miles from current reading. About $3.

GM sending units in the early 2000s had issues with the sulfur in gasoline corroding the contacts in the unit. The gas gauge in my 2000 Blazer stopped working 4 years ago. Since the tank has to be dropped to replace the sending unit, the repair is labor intensive. In the case of my Blazer, I believe the sending unit is built into the fuel pump so the repair would be in the $700-$800 range.

I keep track of the mileage and gallons needed at each fill-up in a notebook. I have a good idea of the mpg year round. I try not to go below 3 gallons in the tank between fill-ups. Knowing the mpg and getting a full tank of gas at each fill-up, I start looking for a gas station at 255 (summer) and 240 miles (winter). Once you know the mpg (I calculate it every 3 or 4 fill-ups) of the Malibu, you should know when to refuel with a healthy reserve.

Ed B.

I agree with the others. You can learn to slap the gas tank to see how much gas is remaining until you get the problem fixed. It works…I used to drive vehicles when I was younger and used this method whenever I was in doubt of the gas tank’s true volume. Dull thud…you have gas. Tinny sound…get some gas quickly.

Yeah, I went for years without a gas guage with a 100 mile commute, They wrecked it when they replaced the tank. I just punched the odometer and computer when I filled up. I always knew how many miles I went and how many gallons I used, but not how much was left in the tank. When the prices zoomed up and down, I just filled up every day for dollar cost averaging.

Thanks for all the tips and advice everyone. I’ll adjust to the problem, just wanted to see if it was worth fixing. I appreciate your time and answers. Thank you! Ally

I disagree with all the above. There is no direct connection between the gas gauge and the amount of gas in the tank. The sending unit sends information to the BCM (body control module) where it is digitized by a codec, then it goes tot he dashboard where the digital signal goes through another codec to be converted to a voltage for the gas gauge. The problem is in the BCM and that is not something that can be fixed for a reasonable cost.

This is another example of GM’s unnecessary use of a computer, or in other words, Rube Goldburg is alive and well and working at GM. Or in other words, If it ain’t broke, then GM will redesign it till it is. Or in other words, To err is human, but to really foul things up, GM will use a computer.

I dunno Keith, my gas gauge problems in my Riviera were clearly caused by the sending unit in the tank and not the BCM. Maybe these symptoms are different but my guage would register low and turn the light on, then sometimes full.

My evidence is it started when my tank was replaced and continued until the pump was replaced and sending unit some years later. The sending unit did the trick, until another couple years later, another pump was installed and they wrecked the $300 sending unit again. Clearly was the sending unit. But if not, you can get a junk yard BCM pretty cheap.

I don’t disagree on all the electronic stuff but still if the signal gets screwed up in the tank, the BCM has no way of knowing its screwed up and just sends the wrong info onto the gauge. The thing that irritated me was the yellow low fuel light was on all the time.

The fact that it jumps around in discrete steps indicates the BCM, and you can’t just use one from a junkyard. If it stayed in one position all the time, then I could see the sending unit as the problem. actually it probably would be worth a try as that is the only affordable repair and since the jumping around only occurs at start, that could be due to the booting process of the BCM.

The lowest cost solution is to reset one of the trip odometers with each fill up and refill after x number of miles, i.e. every 300 miles.

When my gas gauge stopped working I used the trip odometer- and bought a locking gas cap, for a little added insurance. Three years later the fuel pump went, and with the new one came a new sending unit and it works fine.