Hello everyone,

I’m dealing with a persistent and very frustrating electrical problem on my 2018 Skoda Octavia TDI (station wagon). I’m posting here in case someone has experienced something similar or can point me in the right direction.

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SUMMARY OF THE PROBLEM
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After locking the car, the indicator lights (hazards) on the mirrors, front, and rear begin flashing every 5–6 seconds. This continues for hours. Sometimes the interior lights and ambient lights do not turn on when I unlock the car. Occasionally, the car behaves as if some modules do not “wake up.”

The car does NOT have an alarm system installed — only central locking.

This issue happens randomly but consistently, and it can start many hours after the car has been locked.

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WHAT HAS BEEN DONE SO FAR
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1. New Battery Installed
   - Old battery was at 40% life.
   - New battery installed and properly charged.
   - Problem continued.

2. Full System Diagnostics (Launch X431 Turbo II)
   - Multiple modules showed B202300 (Function Limitation Due to Active Protection).
   - Also occasional low-voltage related errors.
   - BCM was accessible and functional.
   - Clearing the errors temporarily stops the issue, but it eventually returns (sometimes after 10–15 hours).

3. BCM Reset / Adaptation
   - Performed full reset/adaptation of BCM.
   - Confirmed BCM reset successfully (ambient light colors changed).
   - Problem returned again after several hours.

4. AdBlue floater reset
   - The AdBlue level sensor had previously been stuck.
   - Reset fixed that issue permanently.
   - Not related to the hazard lights problem.

5. Checked door/boot status
   - All door/boot sensors show correct open/closed state.
   - No errors or anomalies there.

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WHAT I SUSPECT
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• BCM entering protection mode (safe mode) due to intermittent low voltage or abnormal current draw.

• Possible parasitic drain or module that does not enter sleep mode.

• Possible wiring issue (e.g. in boot lid harness) but no visible symptoms yet.

• Possible aftermarket LED license plate light (previous owner) confusing BCM (not confirmed).

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QUESTIONS FOR THE COMMUNITY
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1. Has anyone experienced hazard lights flashing every few seconds AFTER locking the car, without an alarm installed?

2. Have you seen BCM safe-mode behavior triggered by:
   – wiring harness issues,
   – parasitic drain,
   – aftermarket LED lights,
   – door/boot microswitch issues?

3. How does the dealer typically diagnose modules that fail to enter sleep mode?
   Do they check physically with multimeter / thermal camera or only through ODIS?

4. Could the BCM itself be overheating / stuck in an incomplete sleep cycle?

Any advice, similar experiences, or diagnostic suggestions are appreciated. This issue has been extremely time-consuming and stressful, and I would love to hear from anyone who has solved something similar.

Thank you!

22 minutes ago, George_Gr said:

1. New Battery Installed
   - Old battery was at 40% life.
   - New battery installed and properly charged.
   - Problem continued.

Was the BMS coding changed when the new battery was installed?

Yes my friend, i done this

LED Light from Factory?

i am not sure about the led lights of the trunk. but i remember something simillar by my brothers car, when he installed after market lights, the car showed him a light on the dashboard.

I mean headlights