Hello, I have problem with my Octavia (estate)...

On the left tail light two bulbs (5w) does not have +12V, while all other bulbs (P21W, PY21W) works as usual... Those two bulbs reads out +0.6V (if my multimeter is not lying)

I have checked the wiring as far as I could, everything seems fine... All fuses in the fuse box are OK.

I have error code 00984-Left tail light (M4)- Electrical fault in circuit.

Maybe someone had similar problem, where should I look? 

 

tnx in advance

Once the system has detected a failed bulb it will remove the supply from that bulb, hence you only see 0.6V or so; the actually voltage depends on the input resistance of your meter.

 

There are two common cases. One is a poor earth connection at the negative wire to body stud on the left hand side wheel arch area. As your other bulbs are working this is an unlikely cause.

The second cause is poor contact with the bulb, or at the cable connector. This is more likely on a 13 year old car and has been reported before. 

Thank you for reply, however, I was testing directly on the wire (removed from connector for testing), so poor connection to the bulb is out of consoderation 😔

Are the bulbs ok?  Try swapping with other side.

 

I believe the system cuts power to faulting circuits and doesn't restore power until a good load (bulb) is detected even after cycling the ignition so if in the highly unlikely event both bulbs are bad you won't see voltage until you have replaced the bad bulbs and cycled the ignition, not that you'd need to test, the bulb working would be confirmation.

Edited 12 November, 20205 yr by MicMac

3 hours ago, danthe88 said:

Thank you for reply, however, I was testing directly on the wire (removed from connector for testing), so poor connection to the bulb is out of consideration 😔

 

So the failed connection is upstream or a poor earth connection.

With a poor earth connection at the bulb holder, the bulb failure feature will detect no bulb current and shut off its supply (0.6V residual) until the next bulb test soon after start up, So it is correct to see this voltage at the connector in this scenario of no return path.

Could try and clean all the contacts on the bulb holders and plugs- I had a similar problem with my rear lights failing with new bulbs, took all apart, cleaned all contacts and tweaked the lamp contact tabs slightly and it’s been fine since. 

Solved!

The problem was in P21W bulb which was working! I removed all bulbs from left side, and replaced with new ones, than everything started working fine... after that I started putting back old bulbs, and when one P21W was returned 5w bulbs turned off... not sure why, but that caused the problem