obtaining Remaining Fuel Level from a 2004 VW Polo (Mk4)

Question

If I have a 2004 VW Polo and this uses a K-Line Bus (I think), how can I retrieve the fuel Level in the tank if the information is not made available as part of one of the standard OBDII PIDs (I think PID 012F is set aside for Fuel Level).

I know some car manufacturers do not make it easy to get the fuel Level but I know the car can measure the remaining fuel level because a signal of some kind is making its way to the instrument cluster which is showing the fuel Level on a gauge. I am trying to work out is there any way I can issue a query of some kind either using OBD or a more specific query on the K-Line bus to obtain this value.

Any guidance as to what is and isn't possible would be a great help.

Answer 1

If your car does not support the Fuel Level PID (mode 01 PID 2F) then you cannot read it via OBDII. You'll have to figure out how the dashboard instrument panel reads it.

Usually the level is measured by a floater connected to a potentiometer - it's quite likely that the panel is reading an analog voltage signal coming from the fuel sender unit. You could splice into it, the wire shouldn't be hard to find, it would be coming from the rear of the car (the sender unit is often screwed into the tank). Then you could simply measure the voltage (probably 0-12V depending on the fuel level).

Another possibility is that the signal will be PWM, but I've never personally seen the fuel level transmitted this way. In that case you'll need a microcontroller or low pass filter to read it.