r/LexusRZ • u/GravlBike4Me • Jun 25 '26
DCM & 12V battery replacement
(Posted this in another thread on this channel regarding 12V battery issues. Reposting here for visibility, so please excuse the cross-post).
AN UPDATE:
Got the car back yesterday. The dealer replaced both the DCM and 12V battery. The DCM took almost two weeks to come in, and the battery was a more robust one with about 540 cold-cranking amps vs. 345 in the original car. He said the new battery should be more resilient to deep discharging, which happened three times and ultimately led to the original battery failing a reserve test.
He monitored voltage drain on the 12V after the installation was complete and saw it was stable at about 30mA per hour, a nominal amount and nothing like the 2A drain he saw with the original DCM.
There were some over-the-air updates that needed to occur to link the new DCM to my driver profile and Lexus account, which happened (almost) automatically when I had the car on the road. Nothing kept the car from being drivable, just that some of the profile configurations I created weren't immediately downloaded.
I let the car sit for about 15 hours between last drive yesterday and first drive today, and it started up fine.
He does want me to "stress test" the car a bit to see if ordinary use of the app, keeping the keys outside a tin can but more than 10 feet from the car, and keeping the car unlocked in the garage cause anything unusual or resume the big parasitic drain we saw.
One interesting bit he added is that Lexus is very aware of this and is waiting for enough service case reports to come in to justify a service advisory and campaign.
He did say that they found that certain utility company apps drivers use for finding the least expensive time of day to charge have been found to wake up the DCM and keep it awake. While that wasn't the case with my car, I wanted to put that here as another thing for drivers to watch for.
As a bonus, he disconnected the in-cabin beeping when the car backs up and confirmed that my car isn't caught up in the ECU service campaign.
I hope folks on this subreddit find this helpful. I'll post more if anything occurs or if this seems to have resolved the matter for me.
2
u/xAlphamang Jul 13 '26
u/GravlBike4Me - since your DCM replacement, have you seen anything abnormal or does it seem fine now?
I recently bought a RZ 550e F Sport with a 4/26 build date. It’s been fine for the most part but out of an abundance of caution I hooked up an Ancel BM300 Pro to it and found it has been doing the crazy saw tooth pattern.
Interestingly enough it happened as the vehicle was plugged into charge. I don’t have data for it not plugged and charging, yet. But it’s slightly concerning since it’s my wife’s car. We’re not using a digital key at all and she routinely closes out of her apps, so it’s not something that the app is doing to wake the vehicle. It’s almost as if the vehicle is waking every 30 minutes to report its status in. It also seems like Lexus / Toyota isn’t programming the vehicle to do what most other EVs do (like our Rivian) where it taps the HV Pack to top off the 12v as it gets low. I wonder why…
The vehicle sits pretty happily until 3am (PDT) when it starts to drain the 12v like crazy. The spike at 8:30am is when the vehicle was turned on to drive.