2008 ls600hl in the winter Rustbelt, didn't drove the car for about a month and the automatic parking brake is always disabled and I rarely use it to be honest.
Today I drove it a few miles and parked (without parking brake). When leaving about 3 hours later I got a message on the dash stating an electronic parking brake malfunction with the EPB light flashing. Could move the car but a warning popped that the parking brake was engaged. Could not just stay here so drove the car slowly a little bit and felt no resistance or didn't hear any brake noise. After a few second the parking brake engaged warning turned off but the electronic parking brake malfunction warning with the flashing red EPB light stayed on.
Got home and no brake smell so that tell me the parking brake was never engaged and I certainly didn't engaged it myself at any time during that trip. Tried engaging the parking brake and I could hear the actuator but the brake didn't seemed to bite. I could activate it repeatedly and each time the actuator could be heard. While deactivation the sound is exactly the same. Hooked techstream and found code C13A8 (Tension sensor malfunction), C1653 and C13AF. I think C13AF is just a generic ABS code when a EPB malfunction occur and C1653 for the CAN following the malfunction so what matter is C13A8. Repair manual recommend to try first clearing the code, which I did. Warning about the electronic parking brake malfunction disappeared but the EPB light is still flashing red and I don't seems to be able to activate the parking brake. I can hear the actuator but after that I can drive freely.
From what I read the culprit could be the ECU or actuator (which come with all the cable). Car was never in a wreck so I'd be surprise to find water in the trunk around the ECU like some people did after the rear bumper was removed. I though about trying a EPB memory reset in Techstream but the parking brake was never forced on manually so I'm not sure that would help or make the problem worse.
Also would a new ECU or actuator require programming to be compatible with the car (beyond the memory reset procedure) ?
Any help or tips from people that have been in a similar situation would be much appreciated.

Here is the Freeze Frame:

Freeze Frame

 

I just tried a memory reset with Techstream on the parking brake and it did not work. Here is a video of what is happening when the parking brake is engaged:

 

Did you perform "Reset Memory" followed by "Acquire Tensor Sensor Zero Point"?

 

I did not saw the "Acquire Tensor Sensor Zero Point" operation in techstream under the EPB section but in the service manual it state that it should be performed after the parking brake indicator light (RED) turns off, which it did not after the memory reset.

 

Just done performing the "Acquire Tensor Sensor Zero Point" by shorting pin (EPB test mode) but at the step you need to drive 19mph and engage the parking brake it would still not engage.

Edit: I inspected the ECU location in the trunk and no sign of water intrusion. I tried disconnecting the battery for an hour, parking brake light still flashing red. Basically I can drive the car normally and there is actually no DTC stored since I cleared them despite the parking brake not working and the EPB light flashing.

 

Culprit was the Parking Brake ECU which is located next to the 12v battery in the trunk. Replaced with a used one on eBay, light went off right away and parking brake engaged and disengaged without issue. Do be careful when removing the battery carrier bolt because those are extremely easy to break (broke 2 and was super careful for the third one and managed to save it). Ordered new bolt and an extraction kit for the 2 broken ones.

I used part # 89050-50020 which is the newer revision for this part but you could use 89050-50010 as well. I was hopeful it would not be the actual parking brake actuator because those are not cheap and the book says 10.5 hours of labor to replace (I think sub frame need to come down).

 

Did it look like water had anything to do with the failure?

 

I saw no sign of water intrusion in the trunk. Waiting to receive the 2 battery carrier bolt that snapped before physically removing the old ECU (i just unplugged the old one but left it there for now) but I'll certainly take a look at the board and see what happened and post back if something is conclusive.

 

I got the old parts out and upon inspection no damage could be seen on the board, but the plastic on both corner on the back which are next to the 2 biggest chips on the board was pretty deformed which is definitely not normal. It was very hard to pull the board out and the plastic damage was probably caused from the chips overheating. There is a guy on ebay selling a few of them with this picture, which seems to imply that he seen a few of them in similar condition: https://i.ebayimg.com/images/g/-Y0AA...hT/s-l1600.png

After I replaced the part although the parking brake engaged normally the car would move forward on drive (without pressing the gas), as if the tension was not strong enough. Interesting thing is that if I engage the parking brake and put the car in reverse the tension seem to be strong enough to stop the car from rolling (on reverse without pressing the gas) but not on drive. Tried "Reset Memory" and "Acquire Tensor Sensor Zero Point" but no change. Unless I'm not doing the "Acquire Tensor Sensor Zero Point" properly from what I read this step is basically just pressing the parking brake while the light flash after the "Reset Memory" step. When not engage the "target tension" in techstream is showing 0 and 910 while engaged. I think the parking brake need to be mechanically adjusted similar to this video: to get better tension (there is actually a shoe adjusting hole plug on the rear disk).

 

Yes there are a set of drum brakes inside the disc hat that have to be adjusted manually like most other toyota products

 

Ended up manually adjusting the eBrake today and everything is working perfectly now and the eBrake bite strong enough so the car is not moving while on drive anymore. Procedure is the same as in the RX video but the service hole alignment must point to the east (back of the car) and not to the south like in the rx video.

 

Just a follow up to let people know that this issue have still not being resolved. After I replaced the Parking Brake ECU the same warning occurred once more during winter. I cleared it and after that, I put my summer wheels on the car the warning didn't reappear for all summer.

When next winter came I put back the winter wheels and after that the first time I took the car the same warning appeared again, which seems to indicate it may be related to the cold weather. I cleared it a few times but after about 3 starts it reappear again. I cleaned and greased the parking brake but it didn't changed anything. The parking brake engage and release perfectly when I clear the code. 2 times I had to reset the parking brake ECU memory and relearn tension values as clearing the code would leave the parking brake light flashing and the parking brake would not work (no other error would be displayed). I bought the replacement ECU used on ebay so I could have installed a defective ECU with the same problem. The LC500 and ls500 had a recall for Tension sensor malfunction - C13A8 and the fix was to replace the parking brake ECU. I'm not sure which way to go from there beside trying to replace the parking brake ECU for a brand new one because I really don't want to replace the parking brake assembly and I haven't heard of any 4th gen ls which had a parking brake failure. There is a documented case on Youtube for a Toyota Avensis that seems to use a similar parking brake assembly with an error C13A8.

From what I understand, the car is displaying the error because it doesn't like the discrepancy between the tension sensor value (while not engaged) and the tension sensor zero point value (or is it the difference between the 2 sensors?). At no time this error occurred while using the parking brake (and I always leave the auto parking brake button off). Usually it’s right when I start the car or while driving (more rare while driving)

Thanks for any inputs that would help

EDIT: I joined a few pictures of one of the Parking Brake before cleaning. I wonder if a shoe missing too much material could cause this error ? A few days ago after a trip I noticed a burn smell and light smoke on that rear wheel. Not sure if it was the parking brake dragging or a stuck caliper. One of the driver side rear caliper (inward) was at 8% while the other one (outward) was at 50%.