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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.

  • I try to get the fuel level using OBD from mazda 3 2010. 012F returns 'NO DATA'. Nevertheless, It is hard for me to believe that the fuel level is not reported by the ECU. – teddy yossef Feb 18 '17 at 17:46
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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).

Fuel sender pulled out from the tank. Note the potentiometer on the side

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.

  • Thanks for the reply. I figured the Fuel Sender Unit had to be sending something based on the floater device but was hoping not to have to splice into wires. Because VW 2004 cars used K-Line I was hoping there was a way to perform a query (from the OBD Port) to get the signal from the Fuel sender Unit to the Instrument Panel, perhaps even sniffing the data to figure out the signal and then from then on, listen for that signal and retrieve it. I don't need to query using OBDII, perhaps another protocol that can go through the Diagnostic Port. I am not sure if what I want to do possible. – paulboyden Mar 9 '16 at 13:40
  • Well, it's a diagnostic port, so the car will report only the values that are queried. If this PID is unsupported then you won't make the value come out without reprogramming the ECU. The K-Line is simply a communications line for OBDII, the only thing that goes through is what you inquire. If the ECU isn't programmed to give you the fuel level when asked then there is nothing to sniff, I'm afraid. The diagnostic port uses a single protocol for communication. I think your best bet is splicing the wire, maybe someone else can come up with something better. – I have no idea what I'm doing Mar 9 '16 at 15:00
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    Thanks for this. As you say, the bottom line is that if the ECU doesn't report the Fuel then I am not going to get it through the K-Line. I need to start considering what you say about splicing the wire. – paulboyden Mar 9 '16 at 18:02
  • Instead of generic OBD-II readers, have you tried more specific VW diagnostic software? That would tell you if the values are actually exposed at all, possibly in some proprietary way. – Rob Pridham Mar 11 '16 at 9:10

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