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I have a 2005 Mazda 3 (SP 2.3) with roughly 133,000 miles on it. For a couple of years now, my non-driver door locks have not unlocked properly.

The problem is when I use my keyless entry to unlock the car, the driver door unlocks after the first press, but the rest of the doors don’t unlock after the second press (I can hear the driver door trying to unlock again, so I know the signal is getting there). Then I open the driver door, and press the switch on the arm rest and none of the other locks unlock. So I have to reach across and manually unlock them.

This problem has been going in and out, if I had to guess the symptoms seem to show up when the outside temps rise. I know the signal is getting to the locks in question because regardless of the symptoms above being present or dormant, any attempt to lock the doors from the driver seat arm rest switch or the keyless remote is successful.

Any idea what the root cause might be? And does anyone know how to fix it?

  • 1
    Do you mean door locks? I am unsure what a seat lock is. Also, check to see if you have a button that disables all locks except the driver's door lock. I accidentally enabled mine once and it confused me for quite a while :-) – Rory Alsop Feb 27 '18 at 9:59
  • @RoryAlsop Yes, I do mean door locks - modified the question to make that clear. I should have specified in my initial question, but I have checked that and what I would call the "child safety lock" is not enabled, even checked again this morning just in case. – tarheel Feb 27 '18 at 13:47
  • I have just done a tiny edit to make it fully clear, and have upvoted. – Rory Alsop Feb 27 '18 at 13:50
  • Do the power locks work from the passenger switch? Sounds like a wiring or BCM issue. – Ben Feb 27 '18 at 14:42
  • The child safety lock has nothing to do with the actual door lock, what it does is prevent the inside door handle from opening the door. – GdD Feb 27 '18 at 14:47
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Sounds like we can assume the problem as follows: The unlock signal, whether it comes from the fob or the door switch, is failing to complete the circuit somewhere between the unlock module, and the first door. Whether the doors are wired in series or parallel, the fault is clearly upstream of, or at the point where they commonly connect to get the unlock voltage.

I would do some tests to isolate the fault. Looks like from your previous question you can at least take the door apart and know what's going on inside. Start with the passenger front door and find the wire that triggers the lock/unlock. There are a variety of wiring schemes for door locks, but typically you will have one wire that will open the lock when hot, and another that will close it when hot. Look up what your car uses so you know what to expect.

Run a 12v power source (grounded to the frame if it's not from the car's own power) and see if you can trigger the lock/unlock mechanism by applying +12v to each wire respectively, connecting as close to the lock mechanism as possible. My guess is that it will probably work fine, but if it does not, a fault at that point could also cause the other two doors "downstream" to fail.

If it does work on the other hand, you'll have to do some more continuity testing. etc to locate the break. (For example, hook up a multimeter to the lock/unlock wires and see if they get any voltage when you activate the fob or door switch.) Hope that at least gives you something to start with.

  • @ChristoperhHunter Thank you for your answer! Just wanted to let you know I haven't forgotten about it, and plan to do the tests. The problem is that the climate where I live has dropped recently, and the symptoms have disappeared. If there is one thing I know from my time on stackoverflow - can't diagnose the root cause if the symptoms are not there. – tarheel Mar 12 '18 at 17:02
  • Sorry for the insanely long turn around time. I took off the outer panel, and then had to take off the secondary panel to get to the wires mentioned in your answer. I then had to put everything back together because something else came up. It started working after that. I guess my car needed a smack just like an old school TV antenna. Don't know if there is any explanation for it outside of that. Thanks for the help! – tarheel Aug 23 '18 at 1:34

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