Fuel gage is acting up - sending unit?

**trailblazer58** · 10-23-2008, 09:37 AM

This is an '05 Trailblazer I bought new. The fuel gage first started going haywire immediately after I filled up at the gas station (Connoco). Prior to filling the gage was working fine and never had any problems. After filling up, the gas gage needle read zero and the light was on. In addition it gave me the "range low" warning in the driver info system, where it shows all of the range and mpg data, etc. Because the gage seemed to be working somewhat I decided to shut the car off after driving for a couple of blocks to see if it would reset. This did help and the gage came back up to full. On the way home, however, (about 10 miles) the gage gradually started going down, like there was a leak in the tank.

Because I was not absolutely certain there was no leak in the tank, it was a little scary seeing the gas gage going so quickly to empty so I called On-Star and had them run a diagnostic. While doing this the gage started to stabilize and come back up and the diagnostic they ran did not show any problems. The gas gage was actually running normal again for an entire week mostly right up until I filled the tank again. This time it got worse. It took a long time to even get back to normal and I saw it completely cut out from around a quarter tank (when it should have said "full") to empty with the light on and then go back again. It did this twice on the way home. Today it shows almost full again but it's hard to trust the thing. Something is definitely up with it.

Do you think it's the sending unit? Does anybody have any experience changing a sending unit on one of these vehicles or any GM truck? Is it a difficult job? Sorry for all the questions and the long post. I changed a sending unit on an old (now) '88 Toyota truck way back when the truck was about 3 or 4 years old. It was a pain because I had to drop the gas tank. I'm not sure if I want to do it myself this time, or if this is even the problem. That time I was certain it was the sending unit because it always got down to 3/4 tank and then drop to empty. This time I'm not so sure because it's acting eratic. And I can tell this is a much more high tech and accurate fuel gage system than the old Toyota had, which means to me that it may not be as simple a problem as the sending unit only. Any suggestions would be appreciated. TIA

**k.daddy1** · 10-24-2008, 03:54 PM

There is no sending unit, it's part of the fuel pump and you'll have to replace both as an assembly. It's expensive.

**Springthing** · 10-24-2008, 07:06 PM

Pump assembly or gauge problem? I'll go for pump assembly/sending unit.

**trailblazer58** · 10-27-2008, 09:43 AM

What about a bad or poor connection on the ground wire? The fact that it's been working okay in between fill-ups and only malfunctions when I fill the tank makes me wonder if the system is okay but is just not making a proper connection somewhere. If it's a real expensive fix, I will be limping along with it for as long as I can as long as I know I'm not gonna run out of gas! Right now, for example it's working just fine, but I'll need to fill it again soon cause it's approaching 1/4 tank.