GM Flex Fuel Sensor Failures
 

I have now been through 2 "small" GM flex fuel sensors. They have both been genuine ACDelco units but fail in a bizarre way. They will randomly (as far as I can tell) start reading 30-33% ethanol content regardless of actual ethanol content and then after some time slowly go back down or up to the correct ethanol content. I have attached a log showing the issue, just look at the ethanol content throughout the log. At this point, I am tired of the car randomly deciding to run extremely rich for short periods of time when the sensors decide to shit themselves, does anyone have a decent aftermarket sensor that they have found reliable? I'd prefer to have fuel temp as well.

I have swapped the smaller GM flex fuel sensor with the larger GM part (13577379). It worked fine for a short period but is now giving me the exact same symptoms as before:

Randomly misreads ethanol content at around 33% even though fuel temp works, now randomly shows "Flex Fault" on TS with baseline e85 content and 101* (default) fuel temperature.

At this point it has to be my wiring or my ECU. The power (12V) and ground for the sensor are both pulled from the wiper motor connector and the signal wire was ran from the sensor to the DB37 connector on my MSLas MS3 basic. Next step is to test continuity and see if I have issues there, but I cannot understand how the ethanol content suddenly starts reading wrong while the fuel temp works fine if it is a continuity/wiring issue.

Has anyone else experienced this or have any ideas I should try?

Was this car running consistently with the ethanol sensor in place for some period before the sensors started failing?

Have you made any ECU changes, ie firmware updates, lately?

I have yet to get a single sensor working consistently. No firmware or wiring changes since I installed the first one either.

Get both power and sensor ground from the DB37 instead. The ground is critical, get it from pin 3.

That will be easy as I am making a new extension harness for the engine bay anyway. From my understanding the sensor expects 12 bolts (although some have claimed it works on 5). I believe the only 12v source from the DB37 is the fused 12V for the wideband correct?

Generally the sensor works better with 12 volts, not 12 bolts. Maybe 12 bolts if you are really angry with it. :bowrofl: It will not work with 5 volts. Yes, use the wideband 12V source.

But 5 bolts instead of 12 for maximum weight reduction, obviously :noob:

Thanks for the tips!

Just about done with my harness and came across one more question: Should I ground the flex sensor to sensor ground or 12V accessory ground? Logic says sensor ground is best to reduce noise and I assume it’s safe to ground 12V to it but wanted to confirm.

Sensor ground.