We recently diagnosed a 2023 Subaru Forester Wilderness with a severe parasitic battery drain. At times the vehicle was pulling nearly 4 amps with the ignition off.

Subaru considers less than 70 mA acceptable after the vehicle goes to sleep, with roughly 20–35 mA being typical. So this wasn’t a marginal draw. Something was very much awake.

This was a fairly challenging diagnosis, and I suspect this will be a pretty common problem. There’s some evidence that it already is, but since many of these cars are still under warranty, it’s an issue that dealers are likely seeing more often than us. I think this article is probably going to be helpful for many Subaru owners and technicians in the future.

The radio looked guilty

Our first testing pointed toward the audio system. Pulling a fuse associated with the audio power supply (fuse 29 in the under-hood fuse box) made the draw disappear. Disconnecting the audio/navigation unit also eliminated it. We even observed the radio turning itself on with the ignition off.

Bad audio unit (or so we thought). It was Thursday evening and we weren’t going to be able to source a replacement before the weekend. So, we came up with a plan. Unplug the audio unit. Return the car to the customer while he decides if he wants to go with new Subaru unit or get something aftermarket. He won’t be able to listen to music, but he’ll be able to drive without his battery discharging when he parks.

So, we unplugged the radio, reassembled everything, and parked the car so our customer could pick it up the next day.

But the next morning, the battery was dead again. Oops.

So, we started back from square one.

Finding the actual cause

Normally we use voltage drop across fuses to find the source of a draw instead of pulling the fuses one at a time. Our search for the source of the current draw proved pretty frustrating. We kept getting different readings each time we’d check a fuse. It was like the source of the draw was moving around. Sometimes one circuit was pulling current, then it would stop and another circuit was the suspect.

Eventually we found a small aftermarket module under the dash. The label read:

SER: QT 006EB3A4
DOM: 52/23
VER: 47.6
JIG: 11
QT6

The module was connected through an obviously aftermarket harness with multiple taps into the factory wiring.

ChatGPT used the label to identify the component. It’s a KARR BT dealer-installed security system, apparently manufactured by QT Solutions.

This isn’t a Subaru accessory. We checked Subaru’s accessory installation information and found no Subaru alarm system or installation guide corresponding to this equipment.

KARR systems are commonly installed by dealerships for lot security and can remain in the vehicle after it is sold. It’s one of the many items of dubious value that dealerships install on cars to increase the price.

The module wasn’t drawing 4 amps

Here’s the thing that’s unique. The KARR module itself wasn’t drawing much current. It was waking the car up. Unplugging the unit didn’t stop the draw, at least not right away. It would take a while for the current to decrease when we unplugged the module. If we plugged it back in, it would take a will for the current draw to increase.

That behavior can make this type of problem easy to misdiagnose.

The sequence was essentially:

Vehicle asleep → KARR module wakes something → Subaru network wakes → audio and other modules wake → several-amp draw appears

Then:

KARR disconnected → Subaru modules remain awake → shutdown timers expire → current finally drops

The device causing the wake-up doesn’t necessarily have to be the device consuming the current.

The KARR module is connected to more than power

The KARR QT isn’t just a stand-alone alarm that watches a shock sensor and sounds a siren. It interfaces with the vehicle so it can monitor ignition and entry status, lock and unlock the doors, operate the horn, and immobilize the vehicle. The KARR app can also control several of these functions over Bluetooth. Independent analysis of KARR and similar dealer-installed systems found them connected to sensitive vehicle wiring, including the CAN bus, ignition, door locks, horn, lights, and immobilizer circuits. Hilariously, it also found that installing one of these system increases risk of theft.

We weren’t able to find an installation manual for this particular Subaru application, so we can’t say exactly which network or wake circuit this installer used. But this clearly isn’t an electrically isolated accessory. It has both the information and the connections necessary to interact with the car’s body electronics. That provides a very plausible explanation for what we were seeing: the KARR unit didn’t need to consume several amps itself. It only needed to send a message or change the state of a circuit that caused the Subaru’s network to wake up. Once that happened, the factory modules did the heavy lifting—and the heavy current draw.

That explained the radio

Once we understood that, our original radio diagnosis made more sense. The radio wasn’t randomly turning itself on because the radio itself had failed. Something else was waking the vehicle, and the radio was one of the modules responding to that wake-up.

Disconnecting the radio reduced or changed the draw enough to make it look guilty, but the KARR system was still installed and could wake the vehicle again later. That’s why the Forester still killed its battery overnight with the radio disconnected.

This is also a useful reminder when diagnosing modern parasitic draws: Don’t confuse the module that is awake with the module that woke it up.

Subaru’s DCM bulletin is relevant

Subaru has published extensive diagnostic information for battery-drain complaints involving the telematics Data Communication Module, or DCM. One of the main points of Subaru bulletin 15-308-23R is essentially: don’t assume the DCM is causing the battery drain just because it is awake. Prove it.

Subaru specifically warns that modules can remain awake because of other conditions and requires technicians to isolate the actual current source before replacing a DCM. They have also advised technicians to look for aftermarket alarms, remote starts, trackers, and other third-party electrical equipment when diagnosing vehicles that won’t enter sleep mode.

This Forester was a good example of why. The DCM, radio, amplifier, or some combination of factory electronics may account for much of the current once the vehicle wakes up. That doesn’t mean any of those components caused the wake-up.

Some Speculation

The following is just speculation on my part. I have no dealer or manufacturer information.

The fact Subaru issued this bulletin implies that they were receiving many warranty claims for DCMs. They likely started an investigation to find the cause of the failure, and when they did, they found there was no failure.

They state: “Manufacturer evaluations confirm that Gen3/Gen4 DCMs have no consistent parasitic draw issues”.

So, the DCM doesn’t have a problem, but it sure seems like a lot of 2023-2025 Subaru vehicles are having a key off drain problem. Otherwise, why would Subaru issue a TSB addressing DCMs that were misdiagnosed and replaced in an attempt to correct key-off drains?

I think that this device will turn out to be that problem on many Subaru vehicles.

If you find one of these

The module we removed appears to be a KARR BT / QT Solutions security controller. KARR systems are dealer-installed rather than Subaru-specific, so they can appear in many different makes and models. We found evidence of KARR installations on Subaru Forester, Outback, Crosstrek, Ascent, and Impreza models, as well as numerous non-Subaru vehicles.

For this general KARR BT generation, roughly 2017–2026 vehicles are the most likely place to encounter one, although that should not be treated as an application range. A dealer can install aftermarket equipment on an older vehicle as well. The important identifier is the hardware and aftermarket wiring, not the model year.

Give the car time to go back to sleep

There’s one more diagnostic trap worth mentioning. If you unplug one of these modules while the vehicle is drawing several amps, don’t expect the current to fall immediately. The KARR unit may only be supplying the wake-up stimulus. Once the factory modules are awake, they have their own shutdown routines and timers.

Subaru’s parasitic-draw procedure specifies waiting 25–55 minutes for vehicle systems to enter a stable sleep state. So, if you disconnect an aftermarket alarm and the draw remains high for several minutes, don’t immediately conclude that the alarm wasn’t responsible. Watch what happens over time.

In our case, with the KARR system removed, the Forester went through its normal shutdown process and the abnormal wake-up stopped.

The takeaway

This diagnosis initially looked very much like a defective Subaru audio unit. (And it may be that for other technicians it looked like a failed DCM or something else.)

We had:

nearly a 4-amp key-off draw,
a radio that turned itself on,
a fuse that eliminated the draw,
and a draw that disappeared when we disconnected the radio.

All of that evidence had us convinced the audio unit was bad. Luckily, we had the car overnight and realized we were wrong before spending money on misdiagnosis.

The actual problem was a dealer-installed KARR security system waking the vehicle after shutdown. The Subaru electronics were consuming most of the current, but they weren’t the root cause.

So, when diagnosing a Subaru with an unexplained battery drain—particularly one involving the audio system, telematics, or modules that mysteriously refuse to sleep—take a look under the dash before replacing expensive factory electronics. Sometimes the component causing the problem isn’t on the Subaru wiring diagram, because it didn’t come from the factory. It was added by your Subaru dealership before you bought the car.

Also, if you’re thinking, ‘I don’t have an alarm system, so this can’t be my issue,’ it’s common for dealerships to install accessories and then simply disable them if you don’t agree to pay for them. The labor to remove the device is often more than the cost of the device. Depending on how it was disabled, it may still be an issue even if you have no alarm functionality.

What’s Old Is New Again

Mechanics have been finding aftermarket alarms responsible for key-off battery drains since they became popular in the 1990s. There’s nothing new about that. What was unusual here was how this one caused the drain. The alarm itself wasn’t using much current. It was just badly behaved—waking up the rest of the car by screaming who knows what in the middle of the night and waking all of its neighbors.