gas guage acting up

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2005 Trailblazer. When tank is full, guage reads empty. When gas level drops to between 1/2 and 3/4 it starts reading normally and works fine all the way down. I thought if the guage sender went bad, like a break in the resistor, that it would read normal when full then as the tank level lowered to the break it would suddenly drop to zero. Does this guage work opposite of that, or is it likely that the resistor is corroded and needs some type of cleaner?
 
The Fuel sending unit is bad. Needs replacement. My dad's caravan did the same thing as yours before it was replaced.
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Originally Posted By: another Todd
2005 Trailblazer. When tank is full, guage reads empty. When gas level drops to between 1/2 and 3/4 it starts reading normally and works fine all the way down. I thought if the guage sender went bad, like a break in the resistor, that it would read normal when full then as the tank level lowered to the break it would suddenly drop to zero. Does this guage work opposite of that, or is it likely that the resistor is corroded and needs some type of cleaner?


I got a recall notice or warranty extension about a year ago for my 2004 Avalanche. You might call the dealer and ask if there are any hidden warranties or recalls on the gas gauge. I'm guessing it is the same issue.

A few guys on the Avalanche forums have reported that techron concentrate can fix this problem. I'd run a few tanks of this back to back. It's a problem with the in-tank sensor if I'm not mistaken. It gets gunked up with fuel additives. Techron is supposed to help.
 
Originally Posted By: Jim 5
A few guys on the Avalanche forums have reported that techron concentrate can fix this problem. I'd run a few tanks of this back to back. It's a problem with the in-tank sensor if I'm not mistaken. It gets gunked up with fuel additives. Techron is supposed to help.


You do realize that Techron is a fuel additive? Maybe you didn't mean exactly what you typed?
 
Originally Posted By: benjamming
Originally Posted By: Jim 5
A few guys on the Avalanche forums have reported that techron concentrate can fix this problem. I'd run a few tanks of this back to back. It's a problem with the in-tank sensor if I'm not mistaken. It gets gunked up with fuel additives. Techron is supposed to help.


You do realize that Techron is a fuel additive? Maybe you didn't mean exactly what you typed?


I was of course referring to the additives as well as impurities in the fuel that you pump into your tank at the gas station.
 
Hopefully this might help. I actually received a letter from GM offering to fix this problem if it came up in the next few years. I don't have it anymore because I gave it to the next owner of my Avalanche.

See this thread. It is thought to be Sulpher content from the gasoline that corrodes the in-tank sensor. The rememdy is the GM stuff (which apparently is just techron concentrate).

Trailblazer forum Thread Here



Here’s an excerpt from a GM Bulleting (interestingly, a Saab 9-7x is just a fancy trailblazer with the 5.3 v8 isn’t it?)


Fuel System - GM Fuel System Treatment Plus(R)

Bulletin No.: 05-00-89-078A

Date: September 14, 2006

INFORMATION
Subject:
GM Fuel System Treatment PLUS, Fuel Sending Unit Corrosion and Fuel System Deposits

Models:
2007 and Prior GM Passenger Cars and Trucks (including Saturn)
2003-2007 HUMMER H2
2006-2007 HUMMER H3
2005-2007 Saab 9-7X

Supercede:

This bulletin is being revised to add additional model years and update information. Please discard Corporate Bulletin Number 05-00-89-078 (Section 00 - General Information).

The GM Fuel System Treatment PLUS is not recommended for use with diesel fuel. The GM Fuel System Treatment PLUS is specially formulated for use in gasoline and/or E85 fuels.

GM Fuel System Treatment PLUS

GM Fuel System Treatment PLUS, P/N 88861011 (for U.S. ACDelco(R), use 88861013) (in Canada, 88861012), is now available for use in gasoline engines.

Added Benefits and Uses

The PLUS portion of GM Fuel System Treatment PLUS is the addition of a filmer additive that, when used regularly, can protect fuel system sending units from the corrosive effects of certain sulfur contaminants found in some of today's gasoline.

Sulfur contamination can disrupt electrical continuity of certain fuel sending units and lead to erratic or false fuel gauge readings. With scheduled usage, GM Fuel System Treatment PLUS protects against the effects of harmful sulfurs in gasoline.

The Four Benefits

Just pour in one bottle of the GM Fuel System Treatment PLUS into the fuel tank when refueling around each oil change interval:

Cleans - Sulfur corrosion from fuel gauge sending units.

Prevents - Harmful sulfur components from attacking sensitive fuel system electronics.

Protects - By coating metallic surfaces of the fuel system.

Removes - Engine deposits left from use of poor quality fuels.

NOTE: The interval for using this cleaner is NOW 3000 miles, NOT 1500.




The other alternative is that it is a gauge cluster problem or even as simple as a problem with the wiring harness connector as set out in this bulletin:

Probably in the cluster, starting point is Tech II scantool! Only thing you can check without it is the connector and pins on the cluster. Here's the layout, yellow is the fuel signal.


And also check this connector, Important!
Posted By: Administrator 1 Flag Post For Monitor Review
Shop: Mitchell 1 Admin
Date: 6/29/2007 3:37:12 PM



Models:

2004-2007 Buick Rainier
2002-2007 Chevrolet Trailblazer, Trailblazer EXT, Trailblazer SS
2002-2007 GMC Envoy, Envoy Denali, Envoy XL, Envoy XUV
2002-2004 Oldsmobile Bravada
2005-2007 Saab 97x

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described below.

Condition/Concern:

A vehicle may exhibit: 4WD inoperative, SIR lamp, erratic fuel gauge operation and/or a Service Stability Message. Possible DTCs are C0186, C0196, C0327, C0455, P0452, P0453, P0461, P0462, P0463, P0464 and or U1088. A possible cause of these symptoms is a loose connection or backed out terminal(s) at the C101 connector, a 38-way connector mounted along the under hood fuse block. This harness may be routed tightly around the UBEC that could induce any of the concerns listed.

Recommendation/Instructions:

All terminal connections should be checked in this connector for integrity. Female terminals should be inspected for pin drag and Male terminal should be fully seated in the body cavity of the connector. Be certain that no terminals are bent or damaged in any way. Re-route the harness to prevent future harness and/or connector strain.

Note: When servicing this connector special care should be made not to damage other terminals. Fully seat the connector squarely with both hands and then latch the locking portion of the connector (CPA). Do not use the lock mechanism on the connector to pull the connector halves together as this may cause terminals to bend or a poor connection.

Source: GM Preliminary Information Bulletin #PIT3208D - (06/19/2007)
 
Measure the resistance of the tank unit - no need to take anything apart to check it.
Check it at various tank levels - full of course.
This will identify a sending unit or gauge problem.
 
Originally Posted By: Jim 5
A few guys on the Avalanche forums have reported that techron concentrate can fix this problem. I'd run a few tanks of this back to back.


+1

This will actually fix it sometimes.
 
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