Andy,

Are you saying above that if there is no input to the PCM from the signal wire from the fuel level sensor in the tank at the fuel gauge will read past full?

So that would be an undefined voltage but close to zero volts, yes? Does a GM compatible fuel level sensor then send ground voltage on the signal line when the tank is truly physically full?

P0463 is for the sensing circuit being high, which seems like it would correspond to having too high voltage going to the PCM. And the dash gauge currently reads empty. I'm not sure where that voltage would come from unless something is crossed up in the sender itself from the 12 volt signal that runs the pump.

Since we need 3/4 to 1/4, if we can short it on purpose to get 1/2 or will that only work if everything else is functioning as designed? can we assume that 0 volts equals full, 5 volts equals empty, or is it 12, and proportionally calculate half which would be either 2.5 or 6 volts DC. Then tap into a 12 volt wire /5V wire near the PCM, put two identical resistors in series run to ground, tap in between them, get half the voltage, and send it to the PCM fuel sensor input. I'm thinking 5 volt because it is an input to the PCM.
Might this work?

 

My understanding is that the gage has voltage either 5 or 12 to one side. The other side is connected to the variable resistor in the sender. Open or disconnected wire reads past full. 75 Ohms is full down to less than 1 reads empty or short to ground. This was the old days before BCMs. Now I am not sure without digging into the factory manuals. I have an L series car which is an Opel = European design. Ion is an American car with American design. So I don’t know for sure.

Someone with Ion knowledge could read a sensor and then supply resistance half way between full and empty. The car should run the evap monitor after a cold soak.

 

Thank you Andy.

I'm having a damn hard time locating ion schematics on the net for an '07. Can't use the red line schematics as it is a different engine and a different animal.

I was able to find pinned out descriptions for the BCM connectors and surprisingly I did not see an input for anything except instrument cluster, so I don't know where the input goes for that fuel level sensor. I suspect the PCM ECU ECM whatever that I can't find a pin out for it. A wire trace is always an option and usually not fun but if you're going to do the shunt resistor, I think you'll have to do that anyway at least from the back forward.

DropDead,

Are you able to assist this gentleman with schematics or otherwise? Thank you

 

I'm attaching a pdf file with portions of the 2005-2007 Ion wiring diagrams. It contains diagrams for the BCM, PCM (for both 2.2 and 2.4 L engines), computer data lines, and instrument panel. Disregard the titles in red and blue as they are headers for the next section of the diagrams.

Fuel pump and fuel quantity unit are shown on the PCM diagrams.

 

Thanks for the responses. When I get some free time will try and figure out the fuel level sensor circuit. Will look for bad connections, a wire that is worn/ grounded. When I was driving this car the other night the fuel gauge would read 1/2 a tank at times then drop off to empty. Going to need to look at all the wiring as this car in a previous life was towed behind an RV. Just wish my son would have listened that you do not buy cars with CEL illuminated. Thanks John

 

Awesome, Oldmarine.

Where did those diagrams come from?

 

Great, unplug and check harness resistance at pin 44 on the ecm. Purple wire from the fuel sender. Ohm reading? Looks like ground is empty by the drawing. Pcm tells bcm then bcm tells the dash. Used to be simple but a lot more wires.

 

Two years ago, when I bought my '04 Ion, I found and purchased a digital service manual online for Ions. Don't remember where, and it's not very high quality. Not organized very well either, but it serves the purpose if I search enough.