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Ron Z.
Ron Z., - Chevy Tech -
Category: Chevy
Satisfied Customers: 19043
Experience:  18+yrs experience. State Inspector and Chevy Diagnostics
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My 2000 chevy S10s Service Engine Soon light has come on.

Customer Question

My 2000 chevy S10's "Service Engine Soon" light has come on. I went to Autozone and had them put the diag unit on it and the report indicates that the "fuel type sensor" within the power train control module has an issue.

This truck has a flex fuel system in it meaning I can run thee truck on E85 fuel or Unleaded regular. The truck seems to run fine on either fuel type.

I think it may just be a bad connection but I'm not sure. How can I go about getting this fixed, e.g. getting the light to turn off.
Submitted: 6 years ago.
Category: Chevy
Expert:  Ron Z. replied 6 years ago.

Welcome to! My name is DriveFast71(Ron) and I will do my best to answer all of your questions completely and accurately.


Can you give me the actual "p-code" that was retrieved? (Usually just to the left of the description on the AutoZone print-out)


Customer: replied 6 years ago.

aa1 - Fuel composition sensor defective
aa2 - Check connector and wiring to sensor

Originally, it went on and then when I fiddled with the PCM a little, the light went back off. And then later came back and has stayed on consistently.

Sorry, I didn't have the slip with me, so I had to wait until I got home.
Expert:  Ron Z. replied 6 years ago.

Ok- the P0178 is actually becoming a very common GM problem with the FlexFuel system. Most commonly, this is going to be a faulty Fuel Composition Sensor (aka Flex Fuel Sensor) but make sure you check the wire harness and connector for any loose, broken or rubbed through wires, first. If the visual inspection checks ok, then more than likely, the sensor will need to be replaced. It's located on the driver's side frame rail, front.



Ron Z. and 5 other Chevy Specialists are ready to help you
Customer: replied 6 years ago.
You answer seems sensible and will pay but what's more common in this scenario, a faulty connection or a faulty sensor?

I just looked up the part on line and it's incredibly [email protected]#ING expensive. The price rang is from $180 on ebay to $741 dollars at Autozone.♠

That's a lot of money for a part.

Expert:  Ron Z. replied 6 years ago.
Unfortunately, most commonly is the sensor itself. Like I say, i've been seeing this P0178 more and more lately, and it usually comes down to the sensor. Obviously, check that wire harness, it's always a possibility.
Customer: replied 6 years ago.

Can't I just bypass this this? I've used both E85 and unleaded regular and franyly, I am dissapointd with E85's mileage. So I haven't used it in a while. There a non oem device on the market. I think I would rather do this anyway and then just not use E85 anymore and especially since there is only one station within a 50 mile radius that carries this shit.


Hre is the unit I'm considering getting:


You'll have to cut and past this into you web browser.

Expert:  Ron Z. replied 6 years ago.
I've actually seen this before with another customer. The customer I dealt with had this unit put in place, and it did solve the problem, but only for a short time. I believe it was more a defect/poor design of this particular unit. (If I recall correctly, it was a Suburban 1500, with a 5.3L Flex)
Customer: replied 6 years ago.

So, are you saying, don't do it? I can probably find a standard unit but then there's to two hour install time and the tinyb bit of fuel that spills out. There is another unit that does the same thing. I'll look into it.


Expert:  Ron Z. replied 6 years ago.

To be perfectly honest with you- I have very little experience with these by-pass units, and can only tell you what i've dealt with in other customers. I'm here in Rhode Island, and aside from California, I think we've got THE most anal DMV in the country. We MUST do everything "by the book" here. No by-passes at all! I'd lose my Inspector's License if i got caught installing a "by-pass" and then putting a sticker on that car.


Customer: replied 6 years ago.

That I do not understand. All the emission systems are still there. It's just that someone elects to go with one type of fuel over another. If the sensor tell the systems that it's using unleaded fuel instead of E85, what's the problem here?


Expert:  Ron Z. replied 6 years ago.

There is no problem with it by the view of the vehicle's on-board computer... the problem is with RI DMV. They don't allow units like this. I mean, in all honesty, what they don't know won't hurt them, and as long as the Check Engine Light is not on- it's no big deal. Just at my garage, we don't take the chance.