Remove the left side of the trunk carpet, you will see a vacuum actuator that locks and unlocks the door, it should operate with the door lock, in your case, it may malfunction. On my 92 400E I can just pull the vacuum actuator off by my hand if I don't need the gas door lock.

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99 BMW 540i 6-speed 110K Km
03 SAAB 9-5 wagon 80K Km
92 400E (Sold) 245K km
Still missing the days with the Benz, it kept me busy.