I've read a lot about power lock failures in TR4s over the past couple of days; on this forum and elsewhere. Lots of it about actuators that have failed, and how to replace them. And some posts about all the power locks on all the doors failing; or about unlocking working on all doors, but locking not working. But none that really match the problem I'm having.

Mine is a 2007 SR5 Sport, with 172K miles, and I'm the 3rd owner. In my case, both the rear/back seat doors do not respond to the power lock/unlock functions. Push the unlock button on the key fob, both front doors unlock, back doors do nothing. Push the lock button on the key fob, both front doors lock, back doors do nothing. The same for the lock/unlock button on the driver's door. The same for a double key twist in the key lock on the driver's door. In all cases, the front door locks work perfectly, the back doors do nothing. The only way to unlock the back doors from outside of the vehicle is to unlock and open the front door, reach back into the back seat and manually unlock the door. Similarly, it can only be locked by manually flipping the lock. Also note that the power windows work perfectly on the back doors; both from the window switches on each door, and from the master window switches on the driver's door.

I've checked all the fuses that seemed like they were relevant, and they all look good. But perhaps I missed one that I didn't think was relevant? Any other ideas? I don't think it's a case of 2 bad actuators because it seems very unlikely that 2 actuators would fail at exactly the same time. And the people I bought it from (whom I like to think are trustworthy), say that it just started happening. My working theory was that as they were cleaning it out, unplugging various phone chargers and such, they might have tripped a fuse. But so far, I haven't found it.

Thanks for any help the forum can provide on this one.

Have you looked in both fuse boxes?

There's one under the dash on the driver's side and one under the hood on the driver's side.

I definitely checked fuse #34 under the hood (DR/LCK - Power door lock system - 20A). Not sure which other ones I should check under the hood. Or if I should just willy nilly start pulling fuses and check them all.

In the cabin, under the steering wheel, I checked #15 (ECU-IG - Shift lock control system, power windows, anti-lock brake system, traction control system (2WD models), active traction control system (4WD models), vehicle stability control system, electric moon roof, multiplex communication system, theft deterrent system, rear height control air suspension, tire pressure warning system, driving position memory system - 10A); #18 (SECU/HORN - Theft deterrent system - 10A); and #23 (ACC - Power outlets, outside rear view mirrors, audio system, navigation system, shift lock control system, instrument panel lights, rear seat entertainment system - 7.5A). These all looked good. And again, wasn't sure if it was OK to just start pulling fuses willy nilly and check them.

If it's OK to willy nilly pull fuses and check them, I don't mind doing that. I just wasn't sure if I could do some damage by doing that, or accidentally render the vehicle inoperable.

Yes you can pull any of the fuses without issues for the most part, I would however make sure the ignition is off, and always use a "fuse puller" if you have one, I have seen people using a pair of needle nose pliers and short out a live terminal.

Also I always use a multi-meter to insure a fuse is indeed good by doing a continuity test, I have seen fuses that looked good visually but had a break so small you could miss it looking at it.

Thanks. Will try that and report back. Don't have a multi-meter yet, but it looks like there's a trip to the hardware store in my future.

Ok, got a multi-meter. Checked all the fuses that seemed possibly relevant, and a few that didn't, with the multi-meter. They were all good. Didn't check EVERY fuse. It had gotten dark and it was getting difficult to work. Am off work tomorrow, so will do some more checking during the day. But so far, fuses don't appear to be the issue.

Now that you have a multi-meter, you can use it to see if you're getting power to the rear lock actuators, if you're getting power to them they're bad.

Watched a video on how to remove the rear door panel. Having never used a multi-meter, can you offer any guidance on how to use it to test for signal getting to the actuator?

I found a wiring diagram. I found the diagram for the door lock motor rear LH (driver's side). I identified the wires and the pins in the wiring harness from the diagram. But I don't know what to do next with the multi-meter. Don't know what a proper reading is if it's working vs. not working. Don't know which settings to use on the multi-meter to take a reading.

https://www.youtube.com/watch?v=TdUK6RPdIrA

Thanks. So now I now know generally how to use a multi-meter. But how do I apply that specifically for this test? How do I use it to test whether power is getting to the actuator? I know from the diagram that the wires go into pins 1 and 4, blue/black and blue/red respectively. I know the car battery is supposed to be around 12 volts. So I know to set my meter to 20 volts DC (next highest number up from 12 on the meter). I think I know to ground my black test lead to the car body. And I think I know to stick my red test lead into either of the pins, 1 or 4. And then I think I know to hit the unlock switch on the keyfob. But what should I see on the meter if it's getting power? What should I see if it's not getting power? What I do see, though not sure what it's indicative of, is a fluctuation from 0.00 to 0.02 or 0.03. I think this is telling me it's not getting power. But then again, I don't know WTF I'm doing.

I take that back. I went back out and tried with the lock/unlock button on the driver's door rather than the fob. I may have the pins backward, but for the sake of argument, on pin1 when I lock, I see the meter read 8.xx-10.xx. When I unlock I see .25 or something along those lines. On pin4 when I lock, I see .25ish and when I unlock I see 8.xx-10.xx. Should I take that to mean that it IS getting power to the actuator?

It sounds like it's getting power, the higher reading is the "hot" wire when unlocking and locking, the "hot" voltage to the actuator switches to a different wire depending on if it's unlocking or locking, thusly making the actuator reverse it's action on the locking mechanism.

It's like a battery operated drill when you switch from forward to reverse, the switch reverses the current to the motor and makes it run in the opposite direction.

You would most likely get a reading closer to 12 volts if it wasn't such a quick electrical action to unlock or lock, it takes the multi-meter a fraction of a second to get the full voltage reading, but then again I really don't know the actually voltage draw for the actuator motor, it could only require around 10 volts.

So that would seem to indicate my problem is likely the actuator, yes? If it's getting power there, but nothing's happening...

It would seem so...but I would try and confirm that the 8 to 10 volts is what you should be getting to the actuator, the only way I know to determine that short of knowing what the voltage should be is to pull one of the front door panels and see if you get a similar reading to the front doors.

On retesting, I was getting 10+ (but not 11 or 12) consistently. Is there a logical reason to think that 10 wouldn't be enough to get the job done? Is there a logical reason that I could be getting partial voltage to that location, but not sufficient voltage? I was assuming either I'd have power, or not have power. Had not considered that I could have power, but insufficient power.

Just an FYI, IF you do indeed have bad actuators, a new OEM actuator is going to cost you around $200 each just for the part/s....but the only thing that goes bad on the actuator is a small electrical motor which you can find on eBay for around $10 to $15 each, but it will require that you disassemble the actuator after removing it and replacing the motor, if you're up to the task of doing that, there are a few older post on the forum that will tell you which little motor you need to get, but it will require a little searching to find the posts, I'll try and help find them if you decide to go that route instead of replacing the entire actuator.