2005 Skoda Fabia Ambiente (5-door hatchback)

 

For the last week I have been attempting to track down the cause of a suspected parasitic drain that prevents the car from being started on a Monday morning, having not been used since Friday lunchtime.

 

As part of my process of elimination I pulled Fuse 4 from the dashboard fusebox to disable the interior light, reading lights, boot light, and glovebox light.

 

Upon arriving home from work today and taking the key out of the ignition, I noticed that the interior light had come on, albeit dimly. The switch was in the right-hand Doors position.

 

I have now moved it to the center Off position to disable the light completely, but even when looking at the wiring diagrams I am struggling to understand where the power could possibly be coming from if the fuse has been removed.

 

I would greatly appreciate some advise please?

 

(in the attached photo, the Fuse 4 that I removed is the red one that is the fourth one down from the very top right corner)

In the door-activated switch position, two things have to happen to bring on the interior light. The relay (within J519 unit) which connects fuse 4 to the high side of the bulb must be on, and a FET switch in the same unit must be pulling the low side of the bulb down to ground (as commanded by the door switch). If/when this FET isn't pulling that line down, then there is the possibility of current flowing the wrong way into the bulb, even with F4 absent. How that current returns to earth is a bit of a mystery though.

Try another interior light fitting, and see if the problem goes away. Also/instead, check for non-standard bulbs in the one you've got, and any wiring modifications that may have been done (tapping into the wires to feed other gadgetry).

Ok, but even with the fuse removed and the switch in the center "Off" position I can still turn on the reading lights with their buttons, albeit at about half their normal brightness. Looking at the wiring diagrams, the button just connects the low-side of the bulb to ground, which suggests the high-side (fed from J519) still has some voltage present from somewhere, even with the fuse removed.

 

I can confirm that there is no evidence of any modifications to that circuit.

Oh!

I've got a couple of J519s at home I could have a glance at this evening.

 

Ok thanks.

Out of interest, where is  J519 located? Is it something I could pull as well to test?

Approx above the accelerator pedal. 

Looks like this: https://www.ebay.co.uk/itm/SEAT-IBIZA-MK3-FABIA-MK1-BCM-BODY-CONTROL-MODULE-ECU-6Q2937049F-D4/173779341778?hash=item28760e51d2:g:xaEAAOSw6S9cWavZ

 

Oh it's a whole control module. I was expecting it to just be a single relay plugged in somewhere. So much for that idea then.

Yeah, sorry, should've been clearer.  The relay in question is soldered to the circuit board within. Wondering if maybe there's some monitoring circuit connected to the output side of the relay contacts, or some such. If that were misbehaving, I guess it could supply some current, that might explain what you're seeing.

Ok would be interested to know if that was the case.

 

I am tempted to remove and disconnect the light unit itself and see if the voltage is present at the connector.

 

I have the "Cool White" version of these bulbs installed... so I guess being LED they don't need much voltage or current to light...

 

https://www.osram.com/am/ecat/LEDriving PREMIUM-LED interior lamps-Cars-Automotive Lighting/com/en/GPS01_1140185/PP_EUROPE_Europe_eCat/ZMP_1054686/

Edited 16 April, 20197 yr by davepusey

Ahhhhh. LED bulbs in circuits not designed for them cause no end of trouble.

Well the parasitic draw is still present.

 

In the four and half hours since I arrived at work, the battery has dropped from 12.6V to 12.1V

 

This with both the interior lights fuse removed and the dashcam disconnected.

 

I don't believe it is the battery as it was only purchased and fitted in December of 2016.

Recharge the battery, disconnect the interior light assembly entirely, then see what happens.

Ok I will try that tonight after work.