2006 Chevy Trailblazer

The gas gauge is not working properly. Two years ago it began to move to empty when I would fill the tank up. Then, without explanation, it worked fine until three weeks ago. I was traveling on the Mass Turnpike when the check engine light came on and the gas gauge showed that I had a full tank, when I knew that I had less than half a tank based on the mileage. I took the car to have the code read and discovered the gas gauge sensor was not functioning correctly, the ABS sensor coded, and the coolant system showed a code as well. I took the car to a mechanic who checked out the electrical system and said that he found no problem. I then took the car to another mechanic who immediately said it could be an electrical problem or the fuel pump. The fuel gauge still doesn’t work correctly. I did not have this mechanic look at the car. I filled up the tank and the indicator went to empty immediately. My question is, if the fuel pump is the problem, would it take two years for the pump to malfunction? What else could the problem be, and why doesn’t the mechanic just replace the sensor? No one seems to be concerned about the other two codes for the ABS system and the coolant system. I also should mention that the engine now sounds like a diesel engine on a tractor trailer revving up before you switch gears. I don’t remember the car ever sounding like this before. Also the vehicle has 120,000 miles.


You need to find a better mechanic

Diagnosing a fuel gauge and sender is not rocket science.
Here’s what I would do:
Disconnect the fuel module connector
Connect a decade resistance box to the fuel sender wires going to the cluster
Simulate 1/4, 1/2, 3/4 and full tank
If the gauge shows the corresponding amount of fuel, the gauge and wiring are fine
In that case, the problem’s in the tank (stuck float, faulty sending unit, etc)
So, in one fell swoop, I’ve eliminated the gauge and wiring and have narrowed it down

Another thing the mechanic should do:
Connect a professional level scan tool
Sweep the gauges
If the gauge doesn’t read full when commanded to do so, or empty when commanded to do so, the gauge itself (the whole instrument cluster, in your case) is the problem

Please post the ABS fault code and the coolant system fault code

The strange sound could be the fan clutch

The codes for the ABS are B0455 and B0244. The code for the coolant system is P0128. The fuel sensor code is P0463. Thanks so much for your reply. I hope to find a mechanic that will address the problem correctly and make the necessary repairs. Your information has been very helpful, even though I may not understand what you have written, I can certainly take the information to a new mechanic who should understand the instructions, and if they don’t, then I will know to move on.


P0128 means the engine coolant temperature did not increase enough within a certain time frame.

First check if the coolant level is correct.

More than likely, the code set because the thermostat is stuck open/sluggish.

P0463 “fuel level stuck high primary tank” . . . most likely a stuck fuel sender (float)

Here are the fault code diagnostic parameters for your car (assuming you have the 4.2 engine)


If you wind up needing to buy parts, I highly recommend sticking to AC Delco

As for the other codes, check this out. This person has those exact codes


Thanks! I mentioned to one of the mechanics that it might be a stuck float in the fuel pump. I am so glad to know that I have a little knowledge about my car. I will take all information that you have shared to a mechanic.

@clljhns Good luck

I hope the mechanics diagnose the car in a logical fashion . . .

The fuel level sending unit on those is attached to the fuel pump. Those can go bad without the pump itself going bad. It’s kind of a flimsy apparatus on those and they have been known to go out. The unfortunate part is, you can’t just replace the sensor; you have to replace the entire pump.
The Diesel sound of the engine could be several things. You have to figure out if it’s exhaust leak or valvetrain ticking. Check your exhaust manifold bolts to see if they all still have heads on them. Once again, these trucks are known for popping the heads off and causing an exhaust leak. Valvetrain ticking is a little tougher to diagnose. Does the noise start and stop? Worse or better when the engine first starts up?


You CAN get the fuel level sender by itself

Regular wheelbase

Extended wheelbase

I do agree that it might be best to do the whole module, though. It would be a shame to replace the sender, only to have the pump fail in 2 months time.

A fuel guage reading backwards (reads empty when full & visa versa), could be simply that the sender unit connector is plugged in backwards for some reason. Sometimes when work is being done on a car a mechanic will disconnect a wire to gain needed clearance, and could accidentally hook it up backward. Ask your mechanic to double check the sender unit connector by comparing the wire colors to the schematic.

fyi, some ECM’s (engine computer) monitor the fuel tank level when deciding when to test the evap system. They’ll only do the evap test if the tank is less than 3/4 full and more than 1/4 full for example. If the tank level isn’t registering correctly, this could confuse the ECM, and result in an evap code thrown, when in fact there is no problem with the evap system. Since you didn’t indicate evap codes were part of the problem, not likely to be the cause in this case.


I’ve worked on several GM vehicles, and I believe it’s practically impossible to plug the sender connector in backwards.

Of course, if the connector has been damaged/altered, all bets are off

my apologies @db490 . Last time I had this problem, the sending unit was not available as it’s own part. Thanks for the info!

I meant @db4690

The temp code can cause the engine to run poorly because the computer thinks the engine is cold and making it run rich.


If this were my personal vehicle, I’d do the complete module.

But I can understand that someone may want to save a few bucks . . .