Hello All,
I have a 2001 QX4. Prior to this problem, all doors would unlock with the remote. The first push of the remote unlock button would open the drivers door, the second push of the remote unlock button would unlock the passenger door, both rear doors, and the rear hatch. When the remote lock button was pushed all doors and hatch would lock. Now when I press the remote unlock button once the drivers door unlocks (good), but when I push the remote unlock button again the other doors or hatch will not unlock. I have to unlock them with the drivers door unlock button. Sometime when I unlock them all with the drivers door unlock button, they will unlock and immediately lock on there own. All doors and the hatch still lock with the remote lock button. Both remotes have had the batteries changed and I have reprogrammed the remotes to the car. Thanks in advance for your advice and suggestions.

 

That's not a bad problem for a 20 year old ride! But it's an odd one. Your service manual is here:
https://www.nicoclub.com/service-man...cal+System.pdf
Just below the "viewing window" you can "Click here to download a copy". The description of that system starts on page 270.

There are several fuses and even a circuit breaker powering that "Smart Entrance Control Unit" but I don't think that any of those would cause the problem you're describing because lock and unlock (once) work correctly. Seems more like a computer glitch which could mean that black box is having problems. That box also runs the interior light and horn and flashers which confirm lock and unlock.

Perhaps you could check the wires leading from the car frame into the driver's door - to make sure there are no frayed or broken wires passing through that rubber boot? That's my only idea..

 

Thank your for your reply. Yes, this is a stickler of an issue. I can usually fix anything on this QX4. It's a great vehicle and although it has 225k it's like new. I'll keep looking.

 

Ohhh boy, the "Smart Entrance Control" SEC unit. It's basically what Nissan used BEFORE they switched over to their modern BCM system.

You already know the SEC is reading the signal from the fob, you already know the SEC CAN unlock the other doors since you can do it from the door button. That pretty much narrows it down to a failing SEC unit.

Fortunately it's easy to replace, it's right next to the steering column, it doesn't require any special programming to make it work, it's plug-n-play (disconnect the battery first obviously). You will need to pair your key fob to it though but that's easy.

Take it off first and get a good picture of the label, there were a couple of variations but I think they were basically all the same for Pathfinder/QX4. You will want to get an exact replacement.

 

I replaced the SECU with an exact replacement and the symptoms did not change at all. You're right, it wasn't hard to change out. I don't have all the diagnostic tools, so I may take it in to be diagnosed by the dealership as a last resort. Unless, of course there are any more suggestions to try. Thank you.

 

Sorry that didn't work, it sure seemed like a good guess. Now I'm wondering about the master lock / unlock switches in your driver's door. The "re-locking" is what's odd and I wonder if that's the same issue that's preventing the 2nd fob press from working. Mixed signals to the SECU?

That controller in the door actually does some processing so it's one of our many black boxes. Or the "lock" side of that rocker switch may just be failing? I don't mean to throw YOUR money at it, but be worth a $50 ebay investment:
https://www.ebay.com/itm/22346805405...UAAOSw8bpalDoM

 

Thank you for your reply. It may be worthwhile to give it a try. One other bit of information. I was letting my wife in the passenger side yesterday. Usually, I'll use the manual unlock button on the passenger door to let her in (given the unlock/lock issue). This time I used the unlock switch on the passenger door and all doors unlock and lock immediately. So, to sum, the unlock/lock issue happens with the drivers and passenger door lock/unlock switches, and the second push of the unlock button on the remote (Hmmmm). Thx.

 

You know, it feels more like a hardware or shorted wire issue. Please keep in mind I don't know what I'm talking about, only guessing. For example, I now think I'm wrong about the driver's door piece in your car having any logic circuitry - that happens in later years. Looking at the system's schematic (attached below), it seems that all the lock / unlock switches are just that - switches, which connect to ground to indicate they are being pressed. But that means that any of those switches or wires running to them might be shorting to ground and sending incorrect signals. Your description of the passenger door button unlocking then locking all, would be as if you pressed it 3 times in quick succession. I'm surprised you haven't found the car unlocking and locking itself at random.

I'm not sure how to suggest you troubleshoot this other than disconnecting one pin at a time at the SECunit to see if the behavior improves. Or at least using a meter to test through each pin and switch. Sorry, that's about all I've got...

 

Well after a few hours of testing the pins on the SECU connector, it led me to the rear door actuator. I took of the rear interior panel to the hatch to gain access to the switch. Upon inspection, the plastic clip holding the lock actuator to the locking mechanism was broken and not making a good connection. I used a wire tie wrap to secure it and solved the issue! I don't like wire ties to fix broken connectors so I ordered the actuator and associated wire pigtail on Ebay for $25. Thank you to everyone for your assistance and suggestions troubleshooting this issue!

 

Amazing! Great job on the error tracing. When you get the replacement bits installed, jump back in here to confirm it's fixed.

 

I finally received the rear hatch switch connector, installed it, and it definitely fixed the problem. I've attached a picture of the connector. It just snaps over the rear hatch lock and for some reason (heat, years, etc.) did not fit secure over the switch any longer causing the unlock/lock issue. I found this one on Ebay for $25 free shipping. Thanks again for the replies and assistance in troubleshooting.