why does my BMW 3 Series G20/G21 (2019-2024) rear lights stay on when the car is off

BMW 3 Series G20/G21 (2019-2024)

Error Codes

2-4 hours

Time

medium

Difficulty

medium

Severity

3 min read

586 words

Problem Statement

The rear lights of a BMW 3 Series G20/G21 (2019-2024) remain illuminated even when the vehicle is turned off, indicating a potential electrical issue or malfunction in the lightin

Estimated Time

2-4 hours

⚠️ Safety Warnings

Important safety information - read before proceeding

•Disconnect the battery before working on electrical systems to prevent short circuits.

Symptoms

•Rear lights remain on after the ignition is turned off
•Battery drain when the vehicle is not in use
•Possible warning messages on the dashboard
•Increased heat from the tail light assemblies
•Flickering or dimming of lights when the vehicle is turned off

Diagnostic Steps

1
Inspect the light switch for any malfunction or incorrect setting, ensuring it is in the "off" position.
2
Use an OBD-II scanner to check for any fault codes related to the lighting system.
3
Check the body control module (BCM) settings for any programmed features that may keep the lights on.
4
Inspect the rear light assemblies for any signs of moisture or corrosion that could cause electrical shorts.
5
Verify the operation of the light relay by checking for continuity.
6
Measure voltage at the rear light harness with a multimeter to identify any unusual readings.

Solution

💡 Expert Tip

For complex repairs like this, consider taking photos at each step. This helps if you need to reverse a step or consult with a mechanic. Also, keep all removed parts organized - you may need to reference them during reassembly.

Verification

After completing the repair, verify that the issue has been resolved:

✓Test the affected component to ensure it functions correctly
✓Check for any error codes or warning lights
✓Monitor the vehicle for a few days to ensure the issue does not recur

Prevention Tips

To prevent this issue from occurring again:

•Follow the manufacturer's recommended maintenance schedule
•Address warning signs early before they develop into major issues
•Use quality parts and fluids recommended for your vehicle
•Keep detailed records of all repairs and maintenance

Tools & Equipment Required

•Multimeter
•OBD-II scanner
•Socket set
•Flathead screwdriver

Parts Required

•Replacement light switch (if faulty)
•Replacement bulbs (if needed)

Related Faults

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Diagnostic Steps

1
Inspect the light switch for any malfunction or incorrect setting, ensuring it is in the "off" position.
2
Use an OBD-II scanner to check for any fault codes related to the lighting system.
3
Check the body control module (BCM) settings for any programmed features that may keep the lights on.
4
Inspect the rear light assemblies for any signs of moisture or corrosion that could cause electrical shorts.
5
Verify the operation of the light relay by checking for continuity.
6
Measure voltage at the rear light harness with a multimeter to identify any unusual readings.

Solution

1. Preparation

Gather tools and parts required for the repair.
Disconnect the battery to ensure safety while working on electrical components.
Tools Required: Multimeter, OBD-II scanner, socket set, flathead screwdriver.

2. Inspect and Replace the Light Switch

Remove the light switch from the dashboard:
1. Use a flathead screwdriver to gently pry the switch out.
2. Disconnect the electrical connector.
Test the switch with a multimeter for continuity. If faulty, proceed to replace it.
Install the new switch:
1. Connect the electrical connector.
2. Push the switch back into the dashboard until it clicks into place.

3. Check Body Control Module (BCM) Settings

Reconnect the battery and use the OBD-II scanner:
1. Access BCM settings through the scanner.
2. Look for features related to lighting that may cause the lights to stay on.
3. Reset any incorrect settings and save changes.

4. Inspect Rear Light Assemblies

Remove the rear light assemblies:
1. Open the trunk and locate the retaining screws.
2. Remove screws and gently pull the assembly out.
Check for moisture or corrosion:
1. Clean any corrosion with electrical contact cleaner.
2. Replace any damaged bulbs or sockets if necessary.
Reinstall the assemblies securely.

5. Test Relay and Wiring

Locate the lighting relay in the fuse box:
1. Remove the cover and identify the lighting relay.
2. Swap it with a similar relay to test functionality.
If the issue persists, inspect wiring for shorts:
1. Check harness continuity with a multimeter.
2. Repair any damaged wiring as needed.