Hi,
My 2005 A6 diesel fuel gauge is playing up. It was incorrectly showing empty but is now permanently showing full, with a half empty tank. I know this is a problem with the fuel sender (part of the fuel pump) or possibly the wiring to the fuel sender (a common issue I understand).
So far as I understand, the fuel sender is based on a variable resistor and the fuel level is measured by measuring the resistance to ground, i.e. 0 ohms should be an empty tank and , say, 100 ohms (or whatever is the correct resistance for my sender ???) should be a full tank. For example, if the gauge always shows empty then there is no resistance to ground and perhaps the sender wire and a ground are touching. However, for an always full reading there is 100% resistance, indicating a fault such as a break in the wire.
So, how do I diagnose this with my multimeter before opening up fuel tank and/or replacing the fuel tank and sender unit? I can see the top of the plug has five wires - a chunky earth and power wire at each of the plug, presumably to power the pump, and then three thinner wires in the middle - purple, brown and white. I'm a bit stuck about what to do next. I think there might be two senders and the third wire is to the instrument cluster. Does anyone have a wiring diagram, the pin outs for the plug or better information on this. I'm not sure how to proceed.
Thanks, Keith
My 2005 A6 diesel fuel gauge is playing up. It was incorrectly showing empty but is now permanently showing full, with a half empty tank. I know this is a problem with the fuel sender (part of the fuel pump) or possibly the wiring to the fuel sender (a common issue I understand).
So far as I understand, the fuel sender is based on a variable resistor and the fuel level is measured by measuring the resistance to ground, i.e. 0 ohms should be an empty tank and , say, 100 ohms (or whatever is the correct resistance for my sender ???) should be a full tank. For example, if the gauge always shows empty then there is no resistance to ground and perhaps the sender wire and a ground are touching. However, for an always full reading there is 100% resistance, indicating a fault such as a break in the wire.
So, how do I diagnose this with my multimeter before opening up fuel tank and/or replacing the fuel tank and sender unit? I can see the top of the plug has five wires - a chunky earth and power wire at each of the plug, presumably to power the pump, and then three thinner wires in the middle - purple, brown and white. I'm a bit stuck about what to do next. I think there might be two senders and the third wire is to the instrument cluster. Does anyone have a wiring diagram, the pin outs for the plug or better information on this. I'm not sure how to proceed.
Thanks, Keith