Usually the car door or trunk cannot be opened is caused by the remote key, especially the battery is dead or dying. But the post we will share is a case not caused by key fob, what would be the cause? Below is our repair process including the possible cause’s analysis and how we find the exact cause.
Model: BMW X1
Both two key remotes won’t lock/unlock the door and open the trunk with buttons, but the key blade can open and lock the door, vehicle starts and runs well.
FBD power supply failure, ground or internal fault.
The Lin wiring between FBD and CAS failure.
Both keys’ battery is dead or dying.
Short-circuit or loose connection of the rear window glass antenna;
1. Connect scanner with car to read error code, the result is no code.
2. The key is automatically charged when inserted into the key slot, without removable battery.
3. It is detected in the ABL that the key is fully charged, and the key magnetic field strength in the CAS is 0, indicating that the vehicle cannot accept the key signal or the key cannot send the signal.
4. remove the upper trim of the trunk and measure the key receiver FBD:
Unplug FBD to measure
Power supply Pin4: 12V normal
Ground Pin1 to ground resistance: 0.12Ω normal
Signal (FBD to CAS) Pin6: 4.8V normal
Plug the FBD to measure
Power supply Pin4: 1.8V abnormal
Ground Pin1 to ground resistance: 0.1Ω normal
Signal (FBD to CAS) Pin6: 4.7V normal
5. Through the above measurement data, the power supply of the FBD is abnormal. Measure the power supply with an electric pen. The light of Pin4 is very faint, which means that the 12V supplied is not enough to work with electrical appliances when loaded.
6. As shown in the diagram, it can be seen that the power supply reach the FBD after passing the anti-interference filter. Remove the left side trim of the trunk and see that the FBD has water corrosion, as shown in the below photo.
7. Replace the anti-interference filter, find the cause of water leakage in the trunk and repair it, and replace the corroded plug pins.
8. Test two keys, both work. Finish.
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