I have a 2008 stingray with flex fuel conversion. I am seeing a P0178 "input signal had low voltage" error. I contacted the system designer who stated the sensor rarely fails. He suggested checking connections and wires...which i did...but saw no issues.

Is it safe to drive 8 miles to have it diagnosed? I am thinking the tune should revert to a safe settings when error is experienced. Error appeared shortly after fill up with 91 octane pump gas but that should not be cause of error.

Thank you.

 

An ASME master technician diagnosed my flex fuel error, P0178 as a bad sensor using only a voltmeter I bought exact same GM sensor, installed it and still have error. Tried 3 start stop cycles, no fix. Manually cleared error withmy obd reader and same error came back almost instantly.

Is it possible an error code is "locked" in the ECU so new sensor fixed problem but error persists? Does clearing error require tuner type software access to the ecu to reset a P0178 error? All voltages, continuity checks are correct but I still have an error. The wire from ECU is goos as it supplies 5.6V when not connected to sensor. I really doubt 2 sensors are both bad.

Also, it is impossible to check output frquency of sensor with just a voltmeter? The voltage sent out from ECU (with sensor not plugged in) is 5.56V. When connected, the sensor pulls this signal to ground via square wave with varying frequency based on % Ethanol. So if technician only used a voltmeter, how would he know sensor was bad? He could read a lower voltage based on frequency and it be ok. I can check signal voltage when connected but no idea what it "should" be for my current % Ethanol. Should output be 5 volts with highest Ethanol % or lower voltage with high Ethanol %? Nothing explains voltage vs % Ethanol relationship from sensor.

I know. Lots of questions but I have ready spent $250 on parts and labor with no resolution. Tuner in Phx cannot get to car for 6 weeks so I am trying to fix it if I can.

Thank you.

 

Which tuner are you trying to get in with?

 

If your on pump gas you should be fine to drive it but I wouldn't get on it. If the sensors not reading ittl default to pump gas stoic (as it reads no ethanol content). We just had a similar problem with my cousins set up on his 08. Where are you sourcing power? We we're pulling our ignition hot off one of the coil feeds and it was causing some sort of intermitten issue. I rewired it to an Add-a-circuit in the fuse box on an ignition hot (cant recall which fuse of the top of my bead but i can find out) and it seems to have taken care of his issue. If that doesnt work maybe check your connection at the pin. Sensor should see 12v at the red wire at all times. Also just double check your ground. Our issue was weird as it would drop in and out. Not sure if thats what yours is doing or not but we had a scanner so we could watch it. Never tripped the code though.

Edit: just looked up the code. Says Fuel Composition Sensor low imput which leads me to believe your issue may be on your ground side. I'd double check all your grounds and make sure its making good contact.

 

After replacing sensor, error still there. Ordered new connector to sensor (same coil pack plugs) and no error code in 3 drive sessions. New plug was soldered in with dual wall heat shrink tubing.

I have no idea how a connector which was not unplugged goes bad but it did. Maybe being in engine bay, heat and vibration are cause.

 

wrong. flex fuel sensor works off of 5 volts. check your ground. check to see if the output wire is putting voltage out. should be less than 5 volts. if all connections are good at the sensor.... you will need to see the connector at the ECM and check the connection there. Most of us have to add a pin to the connector to get the voltage reading to the ecm. depending on how your tuner set things up.... you can set the default ethanol reading in case something happens. I have mine setup at 70% so it doesn't go lean if it happens while running e85. if it happens while running 93, mine will be running a bit rich.

 

Showing 12v Keyed source here... I understand the sensor uses a 5v reference but at the Red wire it should read 12v hot if everything is functioning properly, if it doesn't you either have a short to ground or no connection. The white wire is your 5v reference