Riddle Me This: Gas Door Won't Lock

[BimmerM3inGA]

My car is a 1998 M3/4 (9/97 build) and I've owned it since May 2000. The problem I'm having is a minor one and it's been "broken" for a long time. I've just finally decided to do something about it.

The little pin that locks the fuel filler door won't extend and lock the door. I did some troubleshooting the other day and this is what I know so far:

If I extend the plunger on the actuator by hand, it will retract when unlocking the doors.

It doesn't matter if I use the remote control, key in the door, or button on the console - the plunger will not extend to lock the gas door.

I extracted and disassembled the actuator and it's remarkably simple; just a plastic box with a motor and worm gear inside. I applied 12V directly to the motor and it runs in both directions just fine.

I connected a voltage tester to the connector for the actuator and there is voltage when unlocking, but not when locking (probably should've done this first before cracking open the actuator but I was certain the actuator was the problem).

Looking at the wiring diagram in my Bentley manual, it appears that the gas door actuator is on the same circuit as the door lock and trunk lock actuators and doesn't have any separate fuses or relays. And everything else works fine.

So, why would there not be any voltage going to that particular actuator on a lock command, but there is for unlock?

[liilpa09]

I have the exact same issue, would like to know the answer to it!

[BimmerM3inGA]

That makes two of us!

[Blink21Me]

+1

[gregmm6]

Good job on the PMCS. My fuel door lock could have been broken for the entire time that I owned my M3 and I never would have noticed it. Good luck fixing it.

[fcvapor05]

Bad actuator? Did you check to see if the input voltage to the actuator was present and correct during both unlocking and locking? If the signal is right, the only thing that can be wrong is the actuator.

[BimmerM3inGA]

Bad actuator? Did you check to see if the input voltage to the actuator was present and correct during both unlocking and locking? If the signal is right, the only thing that can be wrong is the actuator.

I did check for voltage at the actuator. There is none when locking. But there is voltage for unlocking. The actuator works. I applied voltage directly to it in both directions. It will lock and unlock when I hotwire it.

Hence my confusion. Why would there only be voltage in one direction when every other actuator works and they are all on the same circuit? Unless they're not on the same circuit.

[morsexy]

Same issue as well. Been like that as long as I've owned my 2nd M3.

[s52umass]

I had the same problem when i got my car....i put a strong magnet on the inside of the door and its held up great, no problems the last 4+ years

[hayesburrow]

gots the same problem. Subscribed

[hc1001]

just replace the actuator.

[adevera86]

just replace the actuator.

there ya go... check fuses in the rear as well i cant recall which one it is but those blow typically when the actuator goes bad.

[adilSD]

Hi Guys, sorry for resurrecting an old thread but I have the same problem. Replaced the actuator, still no luck. And on top of it, the alarm won't engage anymore either. I get the turn signals to indicated locking but no alarm function, no engage chirp.
Anything else I could do/check?
Thanks,
Adil

[RRSperry]

Pull the actual alarm brain. (usually tucked up behind the glove box) Check all fuses and connections.

[MasterKwan]

Funny, I didn't even know my car HAD a locking gas cap till I pulled the carpet out of the way inside the trunk. Mine's not working either. Not even sure how to activate it. I did manipulate it manually and the pin doesn't stick out which leads me to believe someone snapped the pin off.

[Cheeto419]

Sorry to necro this thread, but did anyone ever figure out this issue? I see +12V but not -12V on my gas cap actuator connector (2000 Z3). Actuator can be moved in both directions by a 9v battery.