Flex Fuel Sensor Failed Again

[Justinj360]

I just replaced the flex fuel sensor on my 2004 Yukon with the 5.3L flex engine approximately 45 days ago. Today I got a check engine light for the fuel composition sensor again (P0178) and had the same symptoms the last time it went bad. I even cleared the code and it came back the next time I started it. What would cause the sensors to go bad? Am I just that unlucky? Before I replaced it I checked the voltage on the plug and it was correct. I bought the current sensor brand new.

 

[shreksbrother]

That must be aggravating.

If you do not run flex fuel, this is what I did... Only cost $160 and took just a minute or two to install (and no fuel mess!)

www.pointaengineering.com

 

[Justinj360]

That must be aggravating.

If you do not run flex fuel, this is what I did... Only cost $160 and took just a minute or two to install (and no fuel mess!)

www.pointaengineering.com

It is very aggravating because it doesn't make sense. Tonight I got another check engine light (the same P0178 code) on the second new sensor... When I first installed this one the check engine light came back the first time I drove it. Just to be sure I disconnected the battery for about half an hour. Then, for a full week after that there were no symptoms or a check engine light until tonight. Am I missing something here? Is there something else I can check? I'll recheck the voltage in the plug tomorrow but other than that I don't know what to do. If I can't find a way to fix it I will get one of those emulators you mentioned. I just wish I knew what was causing the code because I really doubt it would cause two new sensors to go bad that quickly.

 

[Justinj360]

Does anyone else have any ideas?

 

[Justinj360]

SOLVED: Turns out it doesn't like when you mix new and old oxygen sensors. Just before this problem started happening I replaced my exhaust and the upstream oxygen sensors. I replaced those first because they were easy to get to while I had the exhaust out. I completely forgot about the downstream ones and as soon as I replaced those with new ones all the issues went away. It's been about 4 months now and still no issues!

 

[Justinj360]

It looks like I spoke too soon. The code just started coming back right before my fuel pump died. I had the fuel pump replaced and the code is still constantly on. My theory now is that it could be the new high flow catalytic converters. Is that possible?

 

[rockola1971]

It looks like I spoke too soon. The code just started coming back right before my fuel pump died. I had the fuel pump replaced and the code is still constantly on. My theory now is that it could be the new high flow catalytic converters. Is that possible?

Your fuel composition sensor has nothing to do with your oxygen sensors nor your catalytic converters. Your upstream oxygen sensors detect oxygen level in your exhaust stream and this information is used by the PCM to determine what the pulse width (Open and close time) of your fuel injectors along with input of some other sensors too. Your downstream oxygen sensors perform no function whatsoever for your fuel injection, instead they are there to tell you when you catalytic converters are no longer performing as designed.

Here is a good read https://sparkys-answers.com/2010/03/2004-chevrolet-tahoe-code-p0178.html and troubleshooting for the fuel comp sensor. You need a meter that can measure frequency as well as volts. I would also suggest checking the ground wire resistance to ground and inspect splices or actual ground connection for this wire. This wire would prevent the frequency from getting to spec if the ground connection was bad/dirty/loose/corroded. Check your plug for wire breaks at the plug and dirty or loose connection within the connector (vehicle side).

 

[retiredsparky]

Why not simplify--install the replicator that Adam mentioned above and avoid E85. The only people that benefit over the long haul from E85 are the mechanics who replace the sensors. They are notoriously unreliable.

 

[Justinj360]

Why not simplify--install the replicator that Adam mentioned above and avoid E85. The only people that benefit over the long haul from E85 are the mechanics who replace the sensors. They are notoriously unreliable.

Because I doubt that would solve my problem since I've tried 2 new sensors. Plus everything here has at least 10% ethanol now and I would imagine the flex fuel sensor adjusts for that too.

 

[rockola1971]

Because I doubt that would solve my problem since I've tried 2 new sensors. Plus everything here has at least 10% ethanol now and I would imagine the flex fuel sensor adjusts for that too.

You dont need a fuel comp sensor for 87 octane 10% Ethanol. The non FFV dont have them.