I'm reaching out for some advice regarding an issue with the Mark Levinson stereo system in my 2013 Lexus LS460 LWB equipped with the Ultra Luxury Package.

Upon purchasing the car last year, everything with the stereo was in perfect order until one day I noticed a complete lack of bass from the rear speakers. Surprisingly, the front speakers and the rear door panel speakers seem to be functioning correctly.

I've attempted various troubleshooting steps such as adjusting the balance and testing different inputs like radio, CD, and Bluetooth, but haven't had any success. I also checked the amp fuse to ensure it wasn't the culprit, but the fuse is still operational. If you have any additional troubleshooting methods, I'd greatly appreciate your suggestions.

For those who have experienced a similar issue, I'm specifically curious about accessing the rear subwoofer in the context of the power seats and fridge. I'm aware that some owners of the 2009-2012 models successfully pulled the tray up slightly to reach the subwoofer. However, I'm hesitant about potentially damaging unseen wires or breaking tabs, and I'm also concerned about the rear sunshade.

If anyone has encountered and resolved this problem or has advice on accessing the rear subwoofer in my specific model, your insights would be invaluable. Thanks in advance for your help!

 

If all your other speakers are working normally it's likely just the sub bit the dust, they are kinda crappy anyway.

The amp is in the right side of the trunk beside the spare tire, bolts are under the tie downs for the storage bags. maybe someone here can supply you with a schematic for the amp and you could try connecting another speaker there to confirm the amp is ok before taking out the seat....that's an involved job on your model.
Check the fuse box/s in the trunk too, not sure what's in those.

 

The amp can be nonfunctional and the fuse still intact. I believe it's either left or right side of trunk in the lower fender area. Water intrusion is one possibility. Clear the trunk out and check for signs of water in those low areas. You said lack of bass from rear speakers. The subwoofer gives a moderate thump sound, but a lack of bass isn't necessarily the sub. Maybe I'm just not interpreting your description the way you meant it. Subs do go out, usually ripped loose. If no one can explain deck access, concentrate on the amp. There is United Radio, a repair service that has been recommended here.

 

With you car running hold down "MENU" button and cycle headlights switch on-off-on-off couple of times (I think 3-4 times). This will open this service menu. Go in Failure Diagnostics / System Check. See if any faults shown there. Turn your stereo on and select "SPCheck" button on the right top portion of the screen. This function will allow you to listen whatever you playing at the moment through one speaker at the time. This way you can identify faulty speaker.

 

First time I've seen this. Sounds like a great diagnostic tool. No wrench required.

 

Maybe not so much, my clock hasn't been working for a couple o weeks now and it didn't see a fault there but it did pick up one for the amp which was disconnected when I was looking at some speaker wiring underneath it.
I'm guessing this menu is for assembly line use to verify operation of certain things while going from station to station and for some engineering use.

 

That would explain why it's not posted here in multiple threads. If it didn't pick up on clock issue, no telling if it's dependable for amp issues.

 

I attempted the method you suggested, but I couldn't locate the SPCheck option. Could this be due to your vehicle being newer and having an updated software version?

Is it safe to say there are no issues with the amp if the diagnostic and fuse tests resulted in positive results? Although I haven't had the chance to inspect for water damage yet, it seems reasonable to skip that step if the other tests turned out fine, correct?

 

Nope.. Those checks only for MOST bus comms presence per unit, not 'component health'.

 

The Mark Levinson amps were notorious for failures. Its not inconceivable that the bass amp go out while the rest of the amp is working fine. Call United Radio in NY (315.446.5570 or 800.448.0944) and see what they think.

 

OP is a new member. Probably hasn't done a search for ML amp issues. Suggest he does this to learn that a bad amp is a strong possibility. He doesn't have to take our word for it after he reads all the threads. Calling United is a good idea as they will discuss your symptoms and advise based on years of experience. Better than asking us members.

 

Near 100% chance your amp is pooched.