'04 Impala Gas Gauge Bad

[sbagdon]

The gas gauge on our '04 Impala is always E. Trying to figure out if it's the gauge, the sender, or something in between. Is there an easy way to check the gauge... ground a wire, etc? Other debugging techniques?

To replace the sender appears to be about $30 and a few hours, yet wanted to trouble-shoot before throwing time/money at what might not be the root-cause.

Thanks.

[maxwedge]

Disconnect the sending at or near the tank see if the gage moves, more than likely it is the tank unit, was on mine.

[jyount]

Originally Posted by maxwedge

Disconnect the sending at or near the tank see if the gage moves, more than likely it is the tank unit, was on mine.

Like he said, probably the fuel level sensor. Replaced a bunch of them when I worked at the dealer, particularly around those years. The fuels today make quick work of the pile in them. Not only that, they are probably made in China with next to nothing QC.

[Tech II]

Agree with Max...that sender varies from 40 ohms(E), 140 ohms(1/2), to 240 ohms(F)...so the higher the resistance, the more the gauge swings up towards F....as Max suggested, by disconnecting the harness to the fuel tank, this creates infinite resistance, so the gauge should go to "FULL"(key has to be "on", vehicle not running)...

Didn't work on Chevy's, but I think the fuel module is accessible through the trunk, so the gas tank does not have to be dropped....easy job...messy, and because of the fuel fumes, should not be done in an enclosed area.....

[jyount]

Originally Posted by Tech II

Didn't work on Chevy's, but I think the fuel module is accessible through the trunk, so the gas tank does not have to be dropped....easy job...messy, and because of the fuel fumes, should not be done in an enclosed area.....

Some you can and some you can't. Can't remember specifically that year, but easy enough to see, raise the carpet up like you are pulling the spare and look. I think the Monte's were accessible through the trunk and they are the same platform, but different bodies.

[sbagdon]

Originally Posted by Tech II

Agree with Max...that sender varies from 40 ohms(E), 140 ohms(1/2), to 240 ohms(F)...so the higher the resistance, the more the gauge swings up towards F....as Max suggested, by disconnecting the harness to the fuel tank, this creates infinite resistance, so the gauge should go to "FULL"(key has to be "on", vehicle not running)...

Didn't work on Chevy's, but I think the fuel module is accessible through the trunk, so the gas tank does not have to be dropped....easy job...messy, and because of the fuel fumes, should not be done in an enclosed area.....

That was the part I was missing... if the gauge were good and the sender were bad, what would the behavior of the gauge be? If it's "unplug and it goes to F then it's the sender", that's exactly what I was looking for. Thanks!

There's some write-ups on the web about how to do this, and it appears this year/model can be done completely from the trunk, just watch out for the hose that's pressurized, and fumes.

Thanks to all!

[sbagdon]

They finally came over to debug the harness, and yes, unplugging the sensor at the tank drove the fuel gauge to F. So bad sensor. Looks like I can get it locally for about $36+tax, and the online guides show it taking about an hour to replace. Will update after replacing.