Hello, i have a problem with a Skoda Octavia 3 2015. When i try to start the rear window defogger it stays on for a few seconds and it turns off. This problem appeared after my tailgate was replaced, i've tested the defogger if it is interrupted and it's not, but i've found that it's not receiving 12v from the relay, which is also good because i've also tested it.

What i have found with VCDS is that i have an error in Cent. Electric which appears every time i clear it, with the VCDS test in Basic settings the relay is engaging but it stops after one click and says Aborted due to malfunction. What could be done?

Before the tailgate replacement all was working perfectly

Thursday,17,November,2022,20:05:45:00009
VCDS Version: Release 22.3.0 (x64) Running on Windows 10 x64
www.Ross-Tech.com

                Address 09: Cent. Elect.       Labels: 5Q0-937-08X-MV1.clb
Control Module Part Number: 5Q0 937 084 AH    HW: 5Q0 937 084 AH
  Component and/or Version: BCM MQBAB M+  H18 0137
           Software Coding: 0C020846424702FB47E04000001407080200000000000000000000000000
            Work Shop Code: WSC 53721 001 104857
              ASAM Dataset: EV_BCMCONTI 013000 (SK37)
                       ROD: EV_BCMBOSCH_013.rod
                      VCID: 7EF34BFFF9F77C7FB0-802A
1 Fault Found:

559893 - Databus 
          U1121 00 [009] - Missing Message
          [New feature! Extended UDS fault detail is only supported by current gen. interfaces]
          Confirmed - Tested Since Memory Clear
             Freeze Frame:
                    Fault Status: 00000001
                    Fault Priority: 6
                    Fault Frequency: 1
                    Reset counter: 140
                    Mileage: 176727 km
                    Date: 2022.11.17
                    Time: 19:56:14

                    Terminal 15 status: On
                    Terminal 50 status: OFF
                    CAN-Bus_aktiv: On
                    Status Bremslichtschalter (HW): OFF
                    Status Bremslichtschalter (CAN): OFF
                    OFF: operated
                    Position lamps: Not operated
                    Automatic high beam assist: Not operated
                    Low beam: Not operated
                    Parking light left: Not operated
                    Parking light right: Not operated
                    last_wakeup: no cause for fault protection
                    Voltage: 12.0 V
                    Outside temperature: 15.5 °C

Edited 17 November, 20223 yr by AndreiG

It sounds like it is detecting a short circuit, it says something in German about it giving 10 test impulses having no more than a 0.5 volt deviation.

 

Maybe it sends out very short impulses to measure the volt drop and isolate the circuit if shorted before it can blow a fuse?

 

If a bodyshop has replaced the tailgate my money is on a short, it could be damaged cables in the bellows/gaiter.

i will remove the trims and try to check the cables. 

i also played with the values of that deviations and if i set it on a lower value, 0.2 for example it’s not stopping the test but it’s turning the relay very rapidly on and of, and also with a higher value of 0.8 it’s turning on and of at a lower rate

 

But i’m concerned about that error because i know that it wasn’t there before the repair and i think it’s something between control units communicating or something

Edited 17 November, 20223 yr by AndreiG

Ok so i’ve managed to test the wires from the relay to the rear window and all is good.

I’ve made a bypass to the relay and powered the defogger directly and it’s receiving 12v, so i’ve got to the BCM or the climatronic button not sending the impulse to the BCM but i don’t have any diagram for it so i don’t know how to test it more.