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On a warm day (low 20s) where the Polo has been parked up during the day and I drive it after I turn on the sidelights. At the same time, the rear fog lamp warning light illuminates as does the lamp itself. After driving for say 10-15 mins, I try the sidelights again and this time the rear fog lamp does not illuminate.
I've had a similar issue in the winter time, especially when the it's foggy and the air is damp, e.g. during November. Any thoughts on the likely cause?

sounds like a short circuit somewhere, but you'd expect that to occur at colder and/or wet weather rather than hot-ish weather

It does exhibit odd behaviour during hot weather and cold weather. Reversal of the power windows left to right and up to down (everything backwards) durign wet winter weather is the most interesting!

The latest oddity I've seen in hot weather is front n/s position lamp on with lights switched off and ignition off. When I went for a drive I put on the side lights and then the rear for came on again!

Update. When switching on side position lamps while engine is running/under way, the instrument cluster LEDs dim.

No 'whoosh' sound when opening the petrol filler cap.

No warning buzzer when sidelights left on (some of the time)

Gear position indicator LED segment not illuminating completely. I thought I had fixed this with the removal of the instrument panel and re-soldering of prime suspect joints.

littlepolo wrote: ↑Mon Jun 26, 2023 9:20 am Update. When switching on side position lamps while engine is running/under way, the instrument cluster LEDs dim.

Is this not intentional? For instance when you need headlights(side position lights on their own are not legal in UK if you are moving) on the ambient lighting level is lower and so if the instrument panel lights stayed at their daylight brightness, then they would be annoying and probably causing your eyes to "close down" a bit and that would reduce your vision of what is going on out with the car.

littlepolo wrote: ↑Sat Jul 29, 2023 3:28 pm No 'whoosh' sound when opening the petrol filler cap.

No warning buzzer when sidelights left on (some of the time)

I'm not convinced that I always notice a "whoosh" when removing the fuel cap to refuel, but I maybe just guessing that bit.

No warning buzzer when side lights are on and you open the driver's door points to a wiring failure or door lock function failure.

RUM4MO wrote: ↑Sat Aug 12, 2023 12:54 pm

littlepolo wrote: ↑Mon Jun 26, 2023 9:20 am Update. When switching on side position lamps while engine is running/under way, the instrument cluster LEDs dim.

Is this not intentional? For instance when you need headlights(side position lights on their own are not legal in UK if you are moving) on the ambient lighting level is lower and so if the instrument panel lights stayed at their daylight brightness, then they would be annoying and probably causing your eyes to "close down" a bit and that would reduce your vision of what is going on out with the car.

That is a very good explanation!

RUM4MO wrote: ↑Sat Aug 12, 2023 12:56 pm

littlepolo wrote: ↑Sat Jul 29, 2023 3:28 pm No 'whoosh' sound when opening the petrol filler cap.

No warning buzzer when sidelights left on (some of the time)

I'm not convinced that I always notice a "whoosh" when removing the fuel cap to refuel, but I maybe just guessing that bit.

No warning buzzer when side lights are on and you open the driver's door points to a wiring failure or door lock function failure.

The thing is, there was a whoosh on occasion (not always) and now there is not.

Yes, potentially a wiring or door lock issue. In total with the strange things going on with the rest of the electrics (crossed electric window operation, fog lamps coming on with side position indicators, and tailgate not unlocking on central locking and intermittent rear wiper operation, etc.) makes me wonder.

Recent fuel consumption calculated at 45mpg (60/40 highway/urban). Knocking has not been such an issue this summer, possibly due to the milder temps.

I was surprised to record 47mpg 60/40 highway/local recently.

Emissions results at recent MOT:

Fast idle
CO 0.00 % vol
HC 11 ppm
Lambda 1.001

Natural idle
CO 0.02 % vol

the fuel filler flap has got a bit of spring in it (from somewhere) and now needs to be held in to be locked (on the key).