I've never used E85 in my Tahoe. A few months ago, I got a CEL P0178, fuel composition sensor circuit low output. It's intermittent, seems to pop up when I'm under half a tank and goes away when I fill up so, I've been putting it off. My tags expire next month so, I purchased a new, aftermarket sensor from Amazon since the dealer wants around $600 for the part alone. I replaced it but, the next day I not only got a P0178 but, also a P0179 fuel composition sensor circuit high output.
I have a bidirectional scan tool so, I looked over the sensor values. On cold start, the sensor showed
On time - 2 ms
Frequency - 52 Hz
Fuel alcohol content - 31%
Over the course of about 2 minutes, as the truck warmed up, I watched the fuel alcohol content drop 1% at a time until it reached a reading of 2% where it held.
I know these sensors are a common problem but, the OEM ones aren't cheap. I don't ever plan on using e85 so, is there a way to bypass this sensor or deactivate it somehow?
Thank you.
I have a bidirectional scan tool so, I looked over the sensor values. On cold start, the sensor showed
On time - 2 ms
Frequency - 52 Hz
Fuel alcohol content - 31%
Over the course of about 2 minutes, as the truck warmed up, I watched the fuel alcohol content drop 1% at a time until it reached a reading of 2% where it held.
I know these sensors are a common problem but, the OEM ones aren't cheap. I don't ever plan on using e85 so, is there a way to bypass this sensor or deactivate it somehow?
Thank you.
Sep 21, 2025 at 7:37 AM
