1997 4Runner, SR5, 3.4L, Significant Modifications
Probably a year or so ago I started noticing that when I came back to my 4Runner after going in to a store or something, ALL the doors would be unlocked. At first I chalked it up to my forgetfulness, but the more it happened, the more I was pretty sure I was locking the door and the truck was unlocking itself. A few months later and it starts doing it while I'm driving. Cruising along, no one is touching anything and all the doors unlock, just like someone was hitting the unlock switch on the door. It was infrequent enough that it was only a mild annoyance and I always keep the 4Runner in the garage, so not a big deal. Fast forward to today and it is almost undrivable. There now seems to be a loose correlation with vibration and frequency of the random unlocking (or could it be linked to temperature of some component? Engine? Interior heat?). When idling in the driveway, maybe one unlock a minute on average, but there have been instances of 5 or 6 unlocks in 10 seconds or less. Accelerate to highway speeds and we have stretches of 20 unlocks in 30 seconds, it happens very consistently. Super annoying. Example video with two unlocks at idle linked here:
https://imgur.com/a/q54XoG3
I do have pretty significant electrical additions. I made my own aftermarket switch system that includes interior switches, and under the hood relays (ground activated) and fuse box. I have a winch and swapped in a rear locker from another rig (that's the fuse tap you see in the video). All of these modifications were years ago though. No new modifications have been made near the time the problem started. I believe unrelated, but the battery has started struggling to hold a charge recently. It is at least 4 years old now and lives a hard life. I've been living out of the country for 18 months and it wasn't getting driven much. Has quite a few jumps on it.
I have checked all fuses under the hood and near the driver's knee, nothing out of the ordinary.
I did a bunch of reading on a few different forums and it sounded like some people have had some similar problems. There were reports of switches or the key unlock getting stuck intermittently. So the first thing I tried was taking off both the driver and passenger door panels and disconnecting all wire connections to the exterior key switches and interior un/lock switches. The problem persisted.
At this point I dove into the wiring diagrams I have, which is unfortunately for a 2002. The 2002s are more complex, but it at least gave me an idea of how the system works. The body ECU on the 2002s have 3 unlock inputs,
I think the 1997s only have 2 unlock inputs although this is one thing I would like confirmed. When those unlock pins ground (switch pressed), the ECU sends a pulse to all the un/lock actuator motors. In the link below I have included the documentation I have.
https://imgur.com/a/linsCFU
Based on that design my next assumption was that somewhere between the switches and the ECU, one of the unlock signal wires had worn through and was grounding out on the body thus sending a false unlock signal. To verify, I followed wires from the switches back to the body ECU via color and DMM continuity test. I then depinned the unlock signal wires from the body ECU connector to isolate the theoretical shorts and plugged the connector back into the ECU. See link above for depiction. Unfortunately, this also did not fix the problem. Unless I am missing an unlock input, it seemed like the ECU was sending the unlock command sporadically without an input signal.
At this point I thought the only other issue could be the body ECU. I have two parts 4Runners out back so I pulled the body ECU out of one of them, part numbers matched, plugged it in, but the issue remains.
I'm back to thinking it's a false signal into the ECU, I'm just not sure from where. Does the security system have any control over the unlocking the doors? Do the 97s have more inputs I'm missing? I don't have a fob, never have, but I guess the truck could have that system equipped and I don't know about it. I'm going to buy TIS tomorrow morning and dig into the exact diagrams it if nobody here has the solution. Thanks for reading.