Fuel gauge not working properly after new battery fitted

[Blugnomad]

Our MY14 Golf Wagon needed a new battery several weeks ago, due to Covid it didn't get used much for a few weeks. On the next fill the gauge stayed up near full until about 500km run and the range to empty didn't change either. In the last quarter of the tank it seemed to be accurate.

It is apparently doing much the same thing on this tank of petrol as well.

Is there anything in the instrumentation that could have been upset by the battery change? The service technician reset the battery capacity via the OBD port after installing it and the voltage was maintained between batteries.

Cheers,

Tony

[gregozedobe]

Because you maintained voltage during the changeover I can't see any reason why it would affect your fuel gauge. Nor should coding for a new battery.

Probably worth checking if you have any error codes recorded, particularly anything to do with the fuel gauge sender or gauge.

Have you checked your battery voltage ? Should be around 14.2 -14.9V when the engine has been running for a few minutes.

If the voltage is OK then my purely speculative guess is it might be the sender (but on-line diagnosis of car faults is a very imprecise "science" )

[sn809]

Our MY14 Golf Wagon needed a new battery several weeks ago, due to Covid it didn't get used much for a few weeks. On the next fill the gauge stayed up near full until about 500km run and the range to empty didn't change either. In the last quarter of the tank it seemed to be accurate.

Tony

If you are willing to experiment a bit, just try another tank full. Most likely there is a fuel level sensor fault. Could be the sensor was near fault and just carked it. Does the range change as well?
If yo have a VCDS cable, it can help diagnose instrument cluster 17 is where the fuel level settings are.

[DV52]

The fuel gauge needle position can be adjusted on Mk7's - but you need access to a diagnostic cable like VCDS, or OBD11. But this facility modifies the overall reading - it won't change the "linearity" of the measurement across the entire sweep range

For VCDS it's done like this (OBD11 instructions are similar):

1. Select Instrument control module @ address hex17
2. Enter security code: 20103 if build year before MY15, or 47115 if after
3. Select Adaptation and find "IDE02818-IDE02689-Offset for tank calibration values-Complete tank calibration"
4. Adjust value (factory setting: -12.8 ) range: -12.8 to 8.0 more negative values decrease the needle position, more positive values raise the needle position.

Don

[Blugnomad]

Thanks for the replies, today's report follows :

Based on the trip meter and the fuel consumption since last fill the fuel used is about 30 litres. Range to empty is showing 320km, which means the computer thinks there's about 18~20 litres left. The fuel gauge is now just under half. This is basically what it did the previous tank.

If it continues to be accurate in the second half of the tank I think I'll just wait and see whether it gets unreliable.

Cheers,

Tony