You will need a multimeter. Or anything else that can detect either continuity and/or voltage (12 V) such as a test pen.
So, the issue started about 6 months ago, weird behavior from auto lock on the doors. We thought it was the FOB. Replaced the battery, seemed to help for a bit, issue came back, it was just a coincidence. A few months later issue started happening more and more often until about a week ago when driver side door lock wont lock or unlock at all, with fob or with button on the door. The other 3 doors lock/unlock fine.
1. BCM (Body Control Module) - car's computer
4. Latch actuator
Time to figure out what it is.
I will say straight away, I am not going to explore BCM failure as this usually causes other symptoms/problems in addition to the door locks (such as weird light behavior etc). But BCM replacement is going to be much more expensive than the actuator.
First of, when closing or opening the doors with the button, can anything be heard from the door near the latch, if its a buzzing/whirling sound then the motor in the actuator is likely failing/failed. But this tells you that your electrical is in order. Need to replace the actuator and fuses are probably fine.
In my case its dead silence from that door (while other 3 doors lock/unlock). So we check the fuses first.
Under the steering wheel there is a panel of fuses, to the left of it (on the left wall there is a chart with which fuse does what), There are multiple 10A fuses for the door locks and one 20A fuse. Check all these, if you pull it out it should be pretty obvious if it burned out (burn marks on the inside of the plastic and a broken wire). If unsure can test for continuity across the 2 legs.
My fuses were fine. So we take off the door panel.
1) The switch console on the door (where window/door/mirror switches are), look at the front of it (towards the front of the car) under the silver trim there is a little gap that is taller than the rest of it (up against the door), stick a plastic prying tool in there are gently pop off the panel (can use a small screwdriver). Be careful not to scratch the trim. The button console has 2 wires, one for side mirrors other for everything else. Both of these have a little push button in the middle of the socket, pressing it allows you to easily unplug them (if you have to pull hard you are doing something wrong)
2) Under this panel there is a single screw (Philips) holding the panel to the door, unscrew it.
3) Using a prying tool or simply your fingers, from the bottom of the door pull on the door panel. There are clips that are holding it all around. It should pop off. Some of the clips are likely to fall off and some may break. Be careful. But even the body shops and dealerships break these clips all the time. If the car is several years old they may be brittle due to heat exposure over time. You can google and buy a bag of them for a few buck. Search for "car door panel clips".
4) It will be difficult to take off the part near the top where the door unlock lever is, wiggle the panel back and forth and it should come off (the door lever and trim around it stays attached to the door its not part of the panel). Disconnect the seat position memory buttons cable near the top right.
5) With panel off you will see the cable going to the actuator (on the left side of the door near the latch hole), it also has a little button, press it and disconnect.
6) Grab your multimeter, connect the door button console to the bigger cable (so that the door lock/unlock button works). Put multimeter into continuity mode
And measure continuity between the 2 big sockets:
It does not matter which one is negative which one is positive. You should have continuity.
Additionally switch multimeter to Voltage (12V). And while watching the multimeter press lock/unlock button, you should have momentary pulse. You should see some sort of voltage spike. For one (lock/unlock) it will be positive number, for other it will be negative.
If you have continuity and voltage coming through, then likely issue is the actuator or connection to it and your wiring is fine. Inspect the plug and actuator socket carefully, make sure contacts look like they are supposed to (in screenshot above it looks like right right side may be making poor contact and over time closing/opening the driver door caused the contact to bend far enough to no longer make contact, or simply heat cycles over the year caused the metal to warp). I attempted to connect the actuator pins to the socket via alligator clips and no luck, so unlikely to be bad pins.
Picture: Actuator socket
You could test the actuator by hooking the two bigger prongs to a 12V battery to see if it budges, but be careful not to short things as space is small. You can see an example of that here (not my video):
If there is no continuity or voltage then you likely have a wiring problem. On older Hondas there was an issue where the act of closing/opening the doors would cause the wires that go in the sleeve in the door jamb to break over time. Start there. Also inspect all visible wires while you have the panel off for any signs of corrosion/breakage, maybe a wire was pinched by the panel or something else (like glass going down into the channel).
For the actuator part number is (NOTE THIS IS FOR DRIVER DOOR, OTHER DOORS WILL HAVE DIFFERENT PART NUMBERS): 72150-TRT-A02
It replaced an "A01
" part, I dont know why, but they wouldnt make a new revision if they didnt have to, there is a chance "A01
" was prone to failures.
Out of warranty Honda quoted me $160 for diagnosis, $240 for the actuator and $400 for labor. No need to pay for diagnosis if labor is paid for, so cheapest replacement would be ~$640 plus tax.
The actuator can be found online from OEM parts sellers for ~$150 to $170 shipped. Opening the door/replacing it is an hour maybe two of work (for someone who knows what they are doing its more like 30 minutes).
My part is on the way, so I dont have the steps to take out the actuator and put in a new one, but I know it will involve the 3 torx screws by the latch and possibly the two bolts behind the door panel to get the glass channel out of the way. Ill have to figure it out once I actually get the replacement part.
For reference what I paid:
Latch Assembly L Front
If going in to replace the actuator you will have to remove the plastic weather seal (make sure window is rolled up or it will get in the way), wear gloves as the black goop stuff they use is like tar, extremely sticky and hard to wash off anything, you should be able to peel off the plastic and then stick it back on when done. Dont peel the whole thing off, only part that you need to access the actuator.
I wrote this up because there is nearly zero information related to this for Clarity. So hopefully this helps others. Following this should pretty definitively rule in or out wiring up to the actuator socket.