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Flex Fuel Sensor Repair

My hubby’s car needs a flex fuel sensor- 2004 Chevy Tahoe. Sadly he had a stroke a while back; he knows about car repairs but cannot do a lot of the work himself. The dealership quoted $900 to fix this and I would like to have he and my father replace the sensor. We cannot find out any info on where this part is located in th engine and if it can be replaced easily. Any help would be appreciated!

Maybe get a quote from a local mechanic, they are usually a little more reasonable than the dealer.

If you guy insist on DIY, look into getting a repair manual (Haynes is halfway decent for the price). It should show you, step by step how to replace the part.


I would think the sensor would be in the gas tank, but the manual will tell. How do you know it’s bad?

Yes, what happens now that it is bad? If adjusts the engine for E85 fuel and its default is 100% gasoline or 10% ethanol in the gas, I wonder if it is even a necessary repair (if you don’t use E85 fuel).

all I can see is the flex fuel sensor is located ‘‘between the fual tank and fuel injectors’’.
That covers a lot of territory. Follow the fuel lines under the truck , looking for a small box, aluminum housing, two fuel lines both on the same side and an electrical plug perpendicular to those.
There ar four little bolt holes as though it’s mounted somewhere.

To see what it looks like go to any parts store online ( like Auto Zone ) and look it up.

There’s a problem with the fuel compensation sensor.

Here’s where it’s located.


Well, here’s what it looks like:

It’s $300-$400 just for the part from Rockauto, so $900 installed by the dealer sounds about right.

If the default is E-10 (regular unleaded) then why spend the money on something you don’t need? Is there a drivability problem? Or is it just a warning light issue…

“Can this repair be avoided?”

This may well be an unneeded, expensive repair.

Does the sensor default to adjust things to run well on gasoline, or gasoline with up to 10% ethanol? I am guessing so. In that case I would let it be, save lots of money, and avoid using E85 fuel. There are many reasons for everyone to avoid E85, but these folks have an extra incentive.

If, as Caddyman asks, there is a warning light on because of the malfunctioning sensor and for no other reason, you could take the sensor out of the warning light circuit. This should be easy. Then, the warning light will turn on only in case of a new, possibly important, issue.

You mentioned taking taking sensor out of warning light circuit. Could I just unplug sensor. How do I take it out of circuit ? thanks

I just removed mine (2004 Z71 Suburban) and sprayed good quality B-12 Chemtool Professional carb cleaner into the fuel ports. After sloshing it around for a while, I noticed I could hear the liquid moving around after a while. My opinion is that the same bad gas that ruined my fuel-pump clogged up my sensor too. I cleaned it out a few more times and reinstalled it. Works fine, can’t smell or see the exhaust anymore (not running rich like before) and there’s no code. You might try this first instead of spending those dimes.

I recently went thru some rock hard snow and had the oxygen sensor connector and the flex fuel sensor connector ripped out, now I am just have 7 wires hanging and need help on connecting the wires to the new pigtail connectors