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Malibu Maxx fuel gauge never goes above 3/4

I just purchased a 2005 Malibu Maxx about three months ago; it only has 19,000 miles on it. The fuel gauge never goes beyond 3/4 when I fill up. It does go down as I drive, so it seems to be working other than not registering full. A friend suggested trying Seafoam. I’ve never heard of that product and I’m wondering if anyone thinks it will help. Is this fuel gauge problem something to worry about? Or should I just keep driving and not worry about it? Any advice is appreciated.

More than likely the float on the fuel pump assembly is hung up. The next time you fill the tank, go under the vehicle and bang on the gas tank with a rubber mallet and see if doing that free’s up the float.



Forget the seafoam. That doesn’t belong in the fuel tank.

Bring the car to a shop and have them diagnose it.

Have the mechanic use a decade resistance box to simulate empty, 1/4, 1/2, 3/4 and full.

If the gauge is capable of displaying what I just mentioned, then the fuel level sender is faulty.

By the way, are you 100% certain that you are actually filling past 3/4?
I’m not insulting you. But if you have evap problems, there might be factors preventing you from actually filling up completely.

What is the specified capacity of the tank? What’s the most gas you’ve ever put in it when the gauge was near empty?

I am going to disagree with the comment that Seafoam does not belong in your gas tank.
In fact, Seafoam can be used as both a gasoline additive and as a very short-term oil additive, albeit for different purposes.

But, to return to the topic of the thread, there is a known issue with GM fuel sensors, resulting from a build-up of sulphur deposits. While GM’s Fuel Level Sensor recall only applies to Trailblazers and perhaps some of their other SUVs, if you take a look at online forums for Corvettes, Cadillacs, and other GM models, you will see that this exact same problem afflicts many GM models.

Just because a specific model has not been recalled for this problem by GM should not be interpreted to mean that the issue is not a problem with that model.

The recommended “fix” (other than replacing the fuel level sensor), is to use a bottle of Techron, or Seafoam, or GM’s own proprietary gasoline additive. All of those products will rid the fuel level sensor of the sulphur deposits, and will usually restore normal functioning of the gauge with just one treatment. That is the good news.

The bad news is that you usually need to repeat this treatment a few times per year in order to avoid problems. However, some GM owners claim that consistent use of Chevron and other “Top Tier” gasolines also prevents this problem from recurring. Perhaps the higher level of detergents in those Top Tier brands (in order to prevent Fuel Level Sensor problems) is one of the reasons why GM recommends using Top Tier gasoline brands.

This link will show you which gasoline retailers are certified as “Top Tier” brands by GM, Toyota, VW, BMW, etc:

@VDCdriver I’m saying straight out that I just flagged a disagree on your post.

There. I said it.

I log onto the official GM website every few weeks. And I’ve never seen any bulletin, document, recall, etc. which specifically mentioned Seafoam as a repair for faulty fuel level senders.

When I worked at the Benz dealer, I obviously had daily access to their technical website. Same thing. No mention of Seafoam or any other cleaner. And Benz had more than their share of faulty senders. No secret there. Part numbers were frequently revised and there were many TSBs.

I’ve logged on to various factory websites over the years. Never was Seafoam mentioned.

I’ve been doing this for awhile. Neither I nor any of my colleagues past or present ever mentioned this stuff.

Never have I worked anywhere that this stuff was stocked. And the places I worked stocked plenty of chemicals, from various manufacturers.

I’m not saying it doesn’t work.

I’m just saying that perhaps it’s not nearly as popular as you claim.

If somebody reading this wants to post an OFFICIAL GM bulletin, document, etc. specifically recommending the use of Seafoam to fix/prevent faulty fuel level senders, I would appreciate that.

Until then, I’m not convinced.

'nuff said.

Those of us in the auto repair industry in the know have used Seafoam for years.

Don’t immediately write something off unless you’ve tried it.


Providing the other guages work ok, it’s unlikely to be the guage voltage regulator. Here’s the 4 likely causes imo.

How it works: The rising fuel level pushes up a float inside the tank, which is attached to a variable resistor (rheostat) on the outside of the tank (the sending unit). The rheostat is connected by wiring to the dashboard guage, and the amount of resistance in the rheostat is measured, and displayed by the fuel guage and associated electronics. What could go wrong?

  1. Sticking (or leaky and sinking) float mechanism in the gas tank. 2. Faulty rheostat attached to the float, in the sender mechanism. 3. Bad connection between the sender and the guage. 4. Faulty guage. 5. Incomplete tank filling due to an evap system problem.

My first guess would be the float or the rheostat. What I’d do first: Fill the tank, then have your mechanic measure the resistance directly on the rheostat (attached to the tank). Does it measure according to the shop manual spec?


I am “in the auto repair industry” and have been for some time.

I simply said I never saw it mentioned in any factory bulletins or documents.

Therefore, I believe it is not recommended by auto manufacturers to fix faulty fuel senders.

It all boils down to who is recommending the use of something.

I am not doubting your experience, abilities, etc.

Wow never thought would see a contentios debate about sea foam, for 7 bucks give it a whirl.

It’s worth 7 bucks for a try, but only if it is known to be compatible with all the materials used in the fuel system. The fuel lines, fuel filter, fuel pump, fuel pressure regulator diaphram, or even the injectors themselves could be damaged if the materials are not compatible.

It Could Be The Fuel Level Gauge Or It Could Be The Fuel Level Sensor (Sending Unit) In The Tank. Some Sensors Have Been Known To Be “Eaten” By Sulfur In Certain Gasolines. The “Fingers” On The Electrical Wiper Portion Of The Sensor, Located On The Float Arm Dissolves.

I have experienced this and pesonally replaced the wiper on two GM cars and I’ve seen what happens and know what fixes it.

However, your symptoms don’e exactly fit with any of the above situations, in my opinion, although diagnosis needs to be done.

GM published a 2 page TSB 04-08-49-025 (Technical Service Bulletin) to help their technicians diagnose a fuel gauge problem found in some 2004 - 2005 Malibu Maxx (only) vehicles. The bulletin addresses customer complaints involving
" Fuel Gauge Does Not Read Full When Fuel Tank is Full ."

On these vehicles with this complaint, GM says the problem is most likely caused by a deformed fuel tank (deformed during production) that does not allow the sending unit arm to travel to the full up position. The fix is to install a new fuel tank 22677577.

So, have somebody check the gauge and sender operation and if they check out, suspect the tank.


SeaFoam is a great product for its intended use, if needed, and that does not include gauge repairs.

Chevron Techron Fuel Additive Has Been Recommended (I Believe, By GM) To Remedy Some Fuel Tank Sender Problems. I Tried It Before Replacing My Sender And It Didn’t Work, But May Have Cleaned Parts Of My Fuel Delivery System, No Harm.

You can get it at an auto parts store and give it a try, according to directions on the bottle. However, if it’s a deformed tank or a faulty gauge or a “dissolved” wiper fingers on the float arm it won’t fix the faulty gauge function problem.


Ok, took it the garage and here is what their notes say: “EEC tested, code PO463. Pinpoint tested and found the fuel sender is out of spec. $555 parts and labor to replace sender.” So this is Greek to me (except the $555 part). I would obviously rather not pay to replace the sender, since I’m still paying for the car itself. Does anyone think the Seafoam or banging on the gas tank would help in light of this diagnosis? Is it something I can just let go?

I would live with it.

As long as the fuel gauge lets you know when it’s time to refuel, at least you’ll never run out of gas.


How would your use of the car improve if the gauge showed that your tank was full?

What really matters is whether the gauge is accurate when the tank is below half full.

@Bijou I would bite the bullet and have the guys replace it.

$555 is not the end of the world.

It tested faulty, after all.

After the repair, fill up the tank. If it doesn’t read full, go back to that shop and complain.

I Have Replaced Two Of These In The Driveway, One In A Bonneville, One In An Impala. It Took About An Hour.

Many places will sell you the entire fuel pump module with pump, filter, sender, etcetera. The sender usually just unplugs and clips into the module. The sender alone, that I purchased at Advance Auto on 08/12/012 cost $22.06+tax (33.99 less discount).

Sometimes the fuel tank has to be dropped down in order to install the sender into the top of the tank.

My Bonneville and Impalas have an access plate in the trunk that allows one to extract the pump module without removing the tank. That’s why 23 bucks and an hour of spare time replaces the sender, not $555. It’s a piece of cake for somebody who knows what they’re looking at.

Check and see if the Maxx has the access plate in the trunk (under the carpet/lining) or below the rear seat bottom/back. It’s a small oval metal plate held in place by six or seven small screws around it’s perimeter. Obiously, it is located above the fuel tank. Look under the car to see where it is.

Then check an auto parts store for the sender. At any rate $555 is insane. You can get this done for far less.