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Tahoe 2002 service engine soone light is on: What are codes 178 and 440? Thanks

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Code p0178 is fuel compensation sensor circuit low input.
Code p0440 is evap emmision control system malfunction.
I retrieved this blog for you on the Flex fuel Issue.

How to fix SES P0178 and P0179 - Flex Fuel Sensor

Tahoe 2002 service engine soone - dot.gif What is Flex Fuel?

A flexible fueled vehicle (FFV) has a single fuel tank, fuel system, and engine. The vehicle is designed to run on unleaded gasoline and an alcohol fuel (usually ethanol) in any mixture. The engine and fuel system in a flex-fuel vehicle must be adapted slightly to run on alcohol fuels because they are corrosive. There must also be a special sensor in the fuel line to analyze the fuel mixture and control the fuel injection and timing to adjust for different fuel compositions.

What Service Engine Soon codes does it throw?

P0178 and P0179 are directly related to the sensor its self

P0178 - Fuel Composition Sensor. Sensor Circuit Low Volts
P0179 - Fuel Composition Sensor. Sensor Circuit High Volts

Can this really effect anything?

Yes, It can cause your truck to run richer then it should.

Also codes (P0440), should go away after replacing the Flex Fuel sensor.

How much does this sensor cost and what is the part number?

There are 2 part numbers (both are the same part):
The first one: 12568450 (older part number)
The second one: 12570260 (most recent)

From a GM dealer this part will run $613
From it runs $350

dealer will charge around $900-1100 to fix!

Where is the sensor located and what does it look like?

Passenger side, Front frame rail. Right behind the wheel well.

It has 2 fuel lines coming out of it and 1 power.

Actual pic from engine area:

Stock picture of the part:

What kind of tools are needed to replace this myself?

Size 13mm Socket
Fuel Line disconnects ($5 - $10)

I CiTahoe 2002 service engine soone - fuelline.jpgrrect one to use:

How long does it take and is it easy?

Yes it is easy, and it takes about 2-3 hours depending on how you go about getting to it. Take your time and be careful! (a little bit of gas will come out of those lines)

I pulled off the passenger side wheel and went thru the wheel well with a friend under the truck helping. Hard to remove I don't recommend a DIYer on this one.

Posted on Aug 29, 2010


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