Member Since: 09 Sep 2024
Location: Latvia
Posts: 5
Tailgate - CJB FET bypass?
Hello.
Upper tailgate started acting up. Sometimes it would open alright, sometimes it would not, and then, out of nowhere, would function again. When not working - no noise, no anything, but the two button combination on dashboard works. Removed tailgate handle, checked the microswitch - it was working, but nevertheless replaced it. Opened the lower tailgate to inspect the actuator - seems to be working well.
After checking all the wiring, didn't find anything wrong, but what I did discover - whenever the release switch is not working, if I unplug and then plug back together the connector under drivers seat (LHD), the switch always works for some time. So this does the thing temporarily, since the switch is not working, I disconnect the connector, put it back together and it is working again. From reading all the possible info on this forum, im quite sure that the FET module on CJB is not working, and it is not replaceable. I also discovered, that I do get 12V at the switch all the time, even when the connector under drivers seat is disconnected, im sure this is a regular thing. This made me start to wonder on how the FET module is working.
Main part:
I THINK, whenever the microswitch at tailgate is pressed, it sends 12v to FET module, and then from FET module, through seperate wiring, the 12v is sent to lock actuator, and it opens. If this is the case, I should be able to bypass the FET module, by simply cutting the black cable at the microswitch, and then connecting it directly to actuator, which would mean that whenever I press the switch, 12V would go directly to actuator instead of going through FET module. I would simply bypass it.
Is this a rational thing to do, or have I misunderstood something, and this would not work?
Any input would be appreciated, I really hate dealing with temporary solutions.
9th Sep 2024 8:24 pm
Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10735
Well if u so what you say, your tailgate would always be able to be unlocked by thieves .
You could add a relay to try and boost the signal from the FET.
So FET operates relay coil. Relay opens motor
If that doesn’t work, try your original plan with some switches in front of cab to disable and remotely trigger
9th Sep 2024 9:15 pm
blaster1232
Member Since: 09 Sep 2024
Location: Latvia
Posts: 5
Thank you indeed Pete for answering to my post.
I would not be too afraid of thieves opening the tailgate, since we have a disco4 and disco sport for going to city. Disco3 is a proper farm car - checking fields, bringing spare parts to tractors, going hunting etc. If I go with my original plan, I will probably install a switch, by which I can disable the 12v in the loom in case I really have to go to town. I just wanted to hear an approval that my idea is possible.
Also - there is no power for lower tailgate button at all, 0v, so with this I could also provide a live 12v to lower tailgate switch, and then wire it directly from lower tailgate button to lower tailgate actuators
9th Sep 2024 9:32 pm
Naki Blake
Member Since: 31 Dec 2021
Location: Taranaki
Posts: 325
I know very little of car electrics so unable to help you there.
I have just a couple of weeks ago installed the Landrover Passion upper tailgate manual release latch on mine in case of an electrical failure or actuator fault. Easy 1 hour install.
Good video on installation on Powerfuluk.com
9th Sep 2024 9:34 pm
Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10735
I’ll try and check the diagrams when I get time.
9th Sep 2024 9:44 pm
blaster1232
Member Since: 09 Sep 2024
Location: Latvia
Posts: 5
Thanks, Pete! Here are the diagrams I found on forum, but if anything, I really cant make much sense out of them.
10th Sep 2024 1:31 pm
Pete K
Member Since: 15 Jan 2016
Location: GL
Posts: 10735
If pressing the 2 dash board buttons always works, then I would think the FET is fine and the problem is in the switch circuitry.
or maybe it thinks the tailgate is open (when it isn't). Do the roof lights go out correctly?
When you press the switch, it grounds the wire to the cjb to request open. (If you are seeing 12v, this is coming from the CJB), but when the button pressed it should be 0v. Is the ground to the switch good?
The open motor requires 12v to open.
I would check the grounds at the switch are good.
10th Sep 2024 1:32 pm
Disco_Mikey
Member Since: 29 May 2007
Location: Dundee, Scotland
Posts: 20855
It's a software thing. Wiring to the latches between D4/RRS are the same, but when using the Sport CJB it's doesn't work. When the D3 software is loaded it works fine
Member Since: 09 Sep 2024
Location: Latvia
Posts: 5
To Pete: It does not think that tailgate is open, no interior lights, no notifications in dash, and I also plugged the code reader to check for live data - it knows when tailgate is closed. Ground to the switch is good, when I press it, it drops to 0v briefly, although I dont remember if it did the same when the switch was ''not working'' (remember, it works for few minutes after i disconnect and reconnect the cjb plug under seat). I know 100% that when it is not working, even attaching separate new ground wire from known good ground to the 12v at switch does nothing. Not to spend your valuable time, I will make futher diagnosis when I get back to farm on friday.
To Disco_Mikey, can you share your knowledge, where do i solder in this relay?
Sorry for not adding wiring pictures to my last post, forgot.
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