UK-POLOS.NET - THE VW Polo Forum

Yes probably it will

Ok guys I’ve scanned the car with obd11

Shows no faults at all, I’ve checked in central electrics and run an output test which does activate a relay click in the bcm for both the heated rear window and the heated mirrors but neither remain working

Any suggestions to fix? Thanks again

Could it be adjusted in long coding?

Apologies I’ve a novice to vag coding etc

Well, if the command to switch these functions inside the BCM does actually switch the relays, then the coding would seem to be correct - so maybe the issue is further along the power supply line(s).

From memory, in VW Group world, where a switchable function switch is provided with an indicator, ie "power on" indicator, that indicator will only "light" if power is actually being sent to the switched load, for instance, if the BCM relay is actually functioning and responding to the switching request, but the/these relay outputs supply to load has blown its fuse, then that indicator will not "light" - but please correct me if I'm wrong.

It only switches the relay(s) though through an output test. In normal conditions when you operate the heated rear window switch or the heated mirror switch nothing happens. The hrw switch led doesn’t illuminate and the mirror heating doesn’t function

Would that indicate coding was incorrect?

Sorry, yes maybe someone has messed up the BCM coding to disable these functions, which is strange as performing at least the HRW would be a default coding for all versions of thus Polo.

I'd still expect these functions to get power just by performing these output tests - that is if everything else wiring wise and fuse wise are okay and the HRW element and mirror heaters are still intact.

Edit:- mind you, a relay making a "relay switching" noise, does not always mean that the contacts are all still working okay - it just means that the signal is getting to the relay coil and the coil is moving the switching elements.

Are you checking for voltage on the rear screen and mirrors with the engine running? Both of these functions are high load heavy consumers of current.

Equally this could be a faulty switch ?

I’m not sure what to do next haha

CarbonChaos wrote: Sun Feb 26, 2023 8:24 pm Are you checking for voltage on the rear screen and mirrors with the engine running? Both of these functions are high load heavy consumers of current.

Equally this could be a faulty switch ?

I’ve tried a new switch on both, no change. Yes engine on and running. No voltage at mirrors, haven’t checked the rear window but with led not illuminating at all I would assume it’s not switching what so ever

Just checking through the various settings, in the can gateway it says front heating/air con is set to 0 should it be set to one?

Get a probe test light, and see if there is power on the fuse, on the rear window defroster etc.

amer6R wrote: Mon Feb 27, 2023 9:50 pm Get a probe test light, and see if there is power on the fuse, on the rear window defroster etc.

I did check the fuses and it’s showing voltage at the fuse, I’m thinking it can only be either coding or a broken wire somewhere or bad Earth?

In the BCM there is an option to enable or disable rear defroster in long coding.

You should also be able to run output test on the derfrosters. If they work then you have a probbably issue with switch.

If it doesnt work then the issue in wires

amer6R wrote: Tue Feb 28, 2023 5:57 am In the BCM there is an option to enable or disable rear defroster in long coding.

You should also be able to run output test on the derfrosters. If they work then you have a probbably issue with switch.

If it doesnt work then the issue in wires

I did run an output test and the led for the defroster illuminates and then you can hear the bcm relay click for both the defroster and mirror heating. But neither work after.

Are they independent circuits? I know they are fused separately but do they function through the same relay in the bcm

I’ve also just pulled back the rubber boot where the loom passes into the tailgate as I thought that could be the location for possible broken wires but the loom appears good (it still has its cloth tape around)

Mine had cloth tape but the wires were broken. Why dont you try taking some measurments on the defroster grid

You dont have any errors stored in bcm?

What happens when you turn the knob on the mirrors to defrost position?