I'm currently in the process of refitting the whole interior back in and now have a brand new issue.

While the Jeep isn't running, the door locks all operate perfectly fine and as normal. When you start it up and press either lock or unlock, all of the locks start buzzing like they are trying to lock/unlock/lock/unlock very rapidly.

I'm going to investigate after work looking mostly at the 4 body to door looms. Yesterday I refit the lower seatbelts for the front and the plastic cover kick panels so that's my guess.

Any other suggestions are welcome and I'll report back my findings.

 

Kind of a weird thing your Jeep has happening to it. I do not exactly know what the problem may be? Possibly, I think I could help in a way by providing some information. That, and I am curious on what you find is causing the problem. My guess is there is a problem on one of the involved circuits. Stating the obvious right there.. I think, specifically, you have a voltage drop occurring somewhere to cause the problem. It could be happening in one of the wires in the door boots maybe? I think it also could be happening specifically with one of the actual switches on the entirety of the larger overal circuit.

Correct me if I am wrong because I do not know.. Does the XJ have a Body Control Module (BCM)? I believe I read somewhere one time that it does not? I know my ZJ and my WJ have a BCM to control courtesy lights, door switches, windows, etc... But, not the XJs? I do not know what does the actual controlling of the locks if this is true? The BCM does this on both of my Jeeps. Whatever does the controlling is where I would go with my test light or voltmeter to find the suspected voltage drop. I also do not know wether it should be 12 VOLTS or 5 VOLTS supplied to all of the switches either? In any case, my guess is that one of the circuits on the overall circuitry associated to the locking mechanisms would not have the proper 5 VOLTS (or 12 VOLTS) happening on it in the proper way it should anymore for some reason.. I mean too little voltage during normal operation, and probably having some, or too much on it when it should not...

The door locks should be operated by a control mechanism (BCM on a WJ or ZJ) switching power to ground. If you look at the wiring diagrams for the locks you would probably see it is the actual switches are what provides the signal to the control mechanism.. The control mechanism switches power to ground.. The ground power runs through a relay or two.. And finally back to operate the switch function. Ussually, there is going to be a primary switch and a terminal switch on the specific circuit. The primary should be in either the driver or the passenger door. The terminal switch is probably the lock switch for on the liftgate.

Since your Jeep is having the problem occur on all of the lock switches like it is.. I think the voltage drop, or problem, is specific to whatever one these is the primary switch (driver or passenger door lock switch)? It does not have to be the primary lock switch to remember though. It could be any of them. Actually, it could even be a non-door lock switch too. It could be one of the courtesy lights switches, or in their wiring as well.. if the circuits are linked in any way. You would have to check a wiring diagram to be sure what all is on the entire larger circuit. All of these things are actually linked on the larger circuit via the control mechanism in all reality. The control mechanism could be bad? But, I doubt that is the case.

What I would do is test at the control mechanism to find the voltage drop. Or, begin by pulling off and disconnecting all of the switches one by one until you find the troubled part of the circuit by eliminating the problem with it pulled like this. The tail liftgate is a prime suspect too, since the location of this one is in a harsh environment being back there in the confines of the liftgate like it is. A lot of corrosion can build up on the liftgate mechanism and mess things up here.. wether it is the actual mechanism sticking or corroded contacts of the liftgate switch.

I would first go around unplugging each lock switch in order to find the problem location. Then, do further investigating here at the location to find the actual primary fault.. the wiring, the switch itself, or the mechanism the switch is controlling. Or, use a voltmeter looking on the control mechanism (BCM for ZJ and WJ) for the problem.

 

So I started by unplugging the passenger door wiring as I have most of the plastics off currently, made no difference. I then unplugged the drivers door wiring and the issue stopped. Plugged it back in and it started again.

What I didn't think of was my immobiliser unit. It has 2 wires that put +12V into the loom to trigger the door locks. I pulled one of it's door lock wires out from my loom and the issue went away, connected it back up and it came back. I then pulled the other wire and the exact same thing happened. It is only affecting it when both wires are connected. When disconnected I measured no voltage on either wire from the imob unit with one connected to the loom or neither.

I have no idea why this has just started but I have a theory on what's causing it because of how I'm going to fix it. I am going to put a diode on each line from the imob so it can only send a voltage and have no back-feeding. I'm wondering if an internal diode has just failed allowing a back-feed of voltage.

I shall report back tomorrow when I try the diodes.

 

It makes perfect sense.

I have a guess as to why it happened. If it has an internal diode.. I wonder what the diodes rating is? The diode would need to short out in order for it to no longer block current flowing in the reverse direction. In order to short the diode out, the current normally passing through it would have to of exceeded the diodes rating at some point in time.

Age and deterioration would normally only cause the circuit inside of the diode to open. If this were the case, it would not pass current in either direction.

 

Diodes in line and the problem is resolved.