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Rear Door (Tailgate) not locking (not the common fault!)

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Rear Door (Tailgate) not locking (not the common fault!)

Postby pcaffrey1 » Mon Jun 05, 2023 2:49 pm

Hi all,

I have a 2016 L4H3 Transit van that will not lock the rear door for me but has no "door ajar" message on the dash (so it is closing). I have tried a number of different things so I will try explain the problem as I understand it!

I first checked the latch was closing correctly and making contact with the striker bolt and all that was working fine with no plastic pieces impeding the closing of the latch.

I checked this forum and seen the rear door harness often breaks at the door hinge point, I pulled the harness through the boot and found no suspect wires. Not yet satisfied I hadn't missed something I done a continuity check on the harness and it all passed so I can now rule out the harness.

Next I bought a replacement door latch as I couldn't hear the door even trying to lock so thought it could be the actuator. The replacement lock didn't solve my problem.

Before doing anything else I thought at this stage to check the fuses for the central locking. Fuse number 1 (Central locking system 2) on the BCM had burnt out, slowly by the looks of it. I replaced it and had no difference in operation.

Next I tried to check the inputs to the rear door harness to try figure out what all of them do but got nowhere with it really. After locking and unlocking many times fuse number 2 (Central locking system 1) burnt out on me, again looked like a slow break. After replacing that too, the rear door still doesn't lock and I'm scratching my head. The main harness has been covered away as the van is converted into a camper van so it's hard to check that wiring for any frays although I know there's no screws going in near it or any sharp edges.

My next option is to send it to the garage but I thought I'd reach out with you before I spend a lot of money at a garage.

Can anyone provide a schematic of rear door lock? I can't find one online and if I could find out which wire(s) are at fault it would be a big help!
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Re: Rear Door (Tailgate) not locking (not the common fault!)

Postby marcrbarker » Tue Jun 06, 2023 5:59 pm

dunno if this helps.
The blown fuse you found likely a red herring to make think there's an electric fault :) Is probably for completely different circuit like electric mirrors
Screenshot_20230606-173115.jpg
Screenshot_20230606-173159.jpg
Screenshot_20230606-174915.jpg
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Re: Rear Door (Tailgate) not locking (not the common fault!)

Postby pcaffrey1 » Wed Jun 07, 2023 9:53 pm

Thanks, that last image is exactly what I'm after for now and with that I can fault find with a bit more clarity. I'll let you know how I get on with it but thanks for sharing these images it's a great step towards finding the issue!
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Re: Rear Door (Tailgate) not locking (not the common fault!)

Postby marcrbarker » Wed Jun 07, 2023 10:27 pm

You can plan logical tests with a schematic. Some tips, temporarily wire an LED or small light bulb across the fuse in question, so you won't have to keep going there testing it each time something stops working.
Most often the underlying problem is something mechanical and not electric.
Electric breakages get blamed as a culprit when they're a victim, plus the hands-on troubleshooting itself can break things too especially on these fragile late model Fords.
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Re: Rear Door (Tailgate) not locking (not the common fault!)

Postby pcaffrey1 » Fri Jun 09, 2023 12:10 pm

Just a quick update on this, the wires to the lock are a different colour to the schematic sent for some reason but there's 2 seperate plugs going to the door, one with violet-orange and grey-black which I've deduced to be the door ajar switch (I've unplugged it and get the system warning for door ajar).

On the other plug I have green-brown, green-white, violet-grey and blue-brown. I managed to do a continuity check on the main harness from the door back to the BCM. They all have great continuity so I thought I'd check if any had continuity with earth. Apart from the obvious grey-black wire, blue-brown was also showing a continuity to earth. I think the blue-brown line is the same as what you've sent on your schematic. This is an assumption based on the gauge of the wire being smaller than the others therefore is unlikely to be powering an actuator.

Marccrbarker, I don't suppose you could share the 117-22 NN section of the Remote entry system please? I just want to check that harness doesn't have a splice back to earth. I'm pretty sure it won't but I'd rather be sure. TIA
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Re: Rear Door (Tailgate) not locking (not the common fault!)

Postby marcrbarker » Fri Jun 09, 2023 2:24 pm

Screenshot_20230609-141629.jpg
Is this it?
Looks like grounding the wire sends the signal.
Screenshot_20230609-141533.jpg

I believe these are the grounding group
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Re: Rear Door (Tailgate) not locking (not the common fault!)

Postby pcaffrey1 » Fri Jun 09, 2023 3:23 pm

I don't think section 117 is exclusively ground points because on your original schematic, there was 117-30 which was for the motors and it's not showing in that grouping.

I did fully disconnect the blue-brown wire to see if being grounded meant it was in unlock state and stopping it from locking but no joy.

My next step is the Ford garage but thanks for your help and I feel like I'm not far from solving the issue, it does appear to be that blue-brown cable so I'll mention that to the technician when I drop it off.
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Re: Rear Door (Tailgate) not locking (not the common fault!)

Postby marcrbarker » Fri Jun 09, 2023 4:28 pm

on schemqtics i could only find one BU-BN to do with locking and that's "cabin unlock sw" in a image posted the only time I'd expect itgrounded is when that switch is closed.
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