V70: Electrical My V70's fuel gauge does not like church! puzzle

[Peter V70 D5]

Sunday mornings I drive my wife eight miles to her church (Where she plays the organ) I wait in the car about 2 hours watching TV on it's own battery.

Ive posted this before but it's happening again after the 2 hours I start the car and the fuel gauge shows empty the warning diesel pump symbol is lit and the miles to empty tank display shows - - before I put this down to parking on a slope and the float sender device sticking in the tank but I now park in the car park which is dead flat. this fault clears after about 5mins drive with the fuel gauge gradually going back to normal and associated warnings clear and miles to empty tank display returns correct.

The above only occurs while parked near the church and never anywhere else.
The only thing I can think is near the church is a small electricity substation housed in a metal cabinet with a yagi beam antenna sticking out the top presumably for transmitting/ receiving data or control purposes. can this data be getting into the processor and disabling the fuel gauge?
Any ideas welcome.

[SwissXC90]

Likely to be interference from the substation
You can determine this easily. Change parking positions next Sunday to another level surface further away from the substation, and observe what happens

[tommyweaves]

It's God's work Peter, "fisher of men". He's cross with you for wasting 2 hours of fishing time!

[Simon Jones]

How much fuel does the gauge show before you stop/after you move away from the church? Does it happen when you don't use the TV for 2 hours?

[cheshired5]

It sounds to me more like a low system voltage issue.
Once driven for a few minutes and the alternator has replenished the battery a little, everything returns to normal.
You could measure voltages before during and after the 2 hour stop and replicate the car use in another place to eliminate interference issues near the church.

[Simon Jones]

I read it that the TV was running on it's own battery, rather than the car battery, but if the latter is the case then it could be a drop in voltage as suggested.

[cheshired5]

Originally Posted by Simon Jones

I read it that the TV was running on it's own battery, rather than the car battery.

I did too but an active car can still pull a decent current drain so if the car battery isn't tip top, you could get unusual behaviour.

[Peter V70 D5]

Originally Posted by Simon Jones

How much fuel does the gauge show before you stop/after you move away from the church? Does it happen when you don't use the TV for 2 hours?

Fuel shows over 1/2 full when I park up, nothing left on in the car for the two hours ,TV uses it.s own battery which is 18 months old but stranger things. happen.

[cheshired5]

Just unlocking my car creates a 4A drain which increases further if the key is in Pos I or II so even though you having nothing turned on, active modules will cause drains of which you may be unaware.

[Simon Jones]

I would eliminate the TV (which generates RF interference) by not watching it on next trip to the church.