2019-2021 Subaru Forester DCM: Solving Battery Drain and Starlink Faults
This guide covers the common failures, replacement costs, and critical programming requirements for the Data Communication Module (DCM) in your Forester.
- The primary failure symptom is a severe parasitic battery drain that can leave you stranded.
- A replacement module MUST be programmed by a Subaru dealer; it is not a plug-and-play part.
- Dealers may be unable or unwilling to program a USED module. You must confirm with your dealer's service department BEFORE buying a used part.
- Cost-effective DIY bypass harnesses are available that solve the battery drain and restore audio, but permanently disable Starlink services.
The #1 Problem: Parasitic Battery Drain
The most common and frustrating issue with the DCM in the 2019-2021 Subaru Forester is a severe parasitic battery drain. Owners often report finding their battery completely dead after the vehicle sits for a day or two. This happens because the DCM fails to enter its low-power sleep mode after the ignition is turned off. Instead, it gets stuck in a loop, continuously trying to communicate with a cellular network. This faulty state can draw a constant 120-140 milliamps (mA), far exceeding Subaru's acceptable limit of 70 mA, and is enough to drain a healthy battery over a weekend.
Known Issues, TSBs, and Warranty Extensions
Subaru is aware of the DCM-related issues and has released several Technical Service Bulletins (TSBs) to help technicians diagnose the problem. There have also been class-action lawsuits related to these failures.
- TSB 15-308-23: Provides dealers with detailed procedures for diagnosing parasitic battery draw where the DCM is the suspected cause.
- TSB 07-199-21R: Specifically referenced for the 2019-2021 Forester for performing parasitic draw tests.
- DCM Warranty Extension: In response to widespread issues, Subaru extended the warranty on the Data Communication Module for many models to 8 years or 100,000 miles. This may cover diagnosis and repair for the battery drain issue.
- DCM Bypass Box (TSB 15-318-24R): For some vehicles, Subaru has authorized the installation of a bypass module that completely removes the DCM from the system, solving the battery drain while preserving the function of the front speakers and microphone.
Symptoms of a Failing Wireless Communication Module
A faulty DCM can cause several distinct problems. While a dead battery is the most common symptom, you may also notice other issues.
- Repeatedly Dead Battery: The vehicle won't start after sitting for a short period, even with a new battery.
- Flashing Red SOS Light: The red light on the overhead console near the SOS button 🎬 Watch a demonstration on fixing the Subaru red STARLINK light issue may flash continuously, indicating a telematics system fault.
- No Audio from Front Speakers or Microphone: Because the front audio channels are routed through the DCM, a module failure can cut sound to the front speakers and disable the Bluetooth microphone for calls.
- MySubaru App Fails: Remote services like locking the doors or starting the engine from the app will not work.
- Diagnostic Trouble Codes: A professional scan tool may find code B2A0C (Communication Error) stored in the telematics system, which is a strong indicator of a failed DCM. Code B2A16 (Immobilizer Key Collation Diagnosis) may also be present, often related to the audio/mic failure.
Diagnosis: Is the DCM Draining Your Battery?
If you suspect the DCM is causing a parasitic draw, a technician can perform a specific test. This involves connecting a multimeter in series with the vehicle's battery to measure the electrical current being drawn while the car is off. After letting the vehicle sit for up to an hour for all modules to go to sleep, the technician will pull the fuse for the DCM 🎬 Watch this step-by-step test for Subaru battery parasitic drain (often labeled "DCM" in the interior fuse panel). If the current draw drops significantly (e.g., from 140mA to under 40mA), the DCM is confirmed as the culprit.
Pro Tip: Before performing a draw test, ensure all aftermarket accessories like dash cams or phone chargers are unplugged, as these can also cause a parasitic drain.
Warning: Simply disconnecting the battery can sometimes temporarily reset a faulty module, making the parasitic draw disappear during the test. This can make diagnosis tricky.
Buying a Used Wireless Communication Module: Read This First!
For most parts, a used OEM component is a great value. For this specific module, extreme caution is required.
A replacement DCM, whether new or used, is NOT plug-and-play. It must be electronically registered to your vehicle's VIN by a Subaru dealer using their proprietary Subaru Select Monitor software. The module has a unique cellular identifier (like a phone's ESN or IMEI) that is tied to the original vehicle in the Starlink system database.
The critical problem is that many Subaru dealers are either unwilling or unable to reprogram a used DCM to a new vehicle. Their internal procedures are often designed for programming new, unassigned modules only. If you install a used DCM, you may fix the battery drain, but you will likely never be able to activate the Starlink telematics features.
Before buying a used DCM, you MUST:
- Call your local Subaru dealer's service department.
- Give them your VIN and explain that you are considering purchasing a used DCM (part numbers 86222SJ100, 86229SJ000, 86229SJ100, or 86229SJ101).
- Ask them directly: "If I bring the car and the used module to you, can you and will you program it to my vehicle?"
- If they say no or are unsure, do not buy the used module expecting to restore Starlink functionality.
If your only goal is to fix the battery drain and restore front speaker audio, and you do not care about Starlink services, a used module may still be a viable option, but the DIY alternatives below are often cheaper and more reliable.
DIY Alternatives to Full Replacement
Given the high cost and programming challenges, many owners opt for a bypass solution. These will permanently disable Starlink services but resolve the battery drain.
1. Aftermarket Bypass Harness
This is the most popular and effective solution. Companies like Auto Harness House sell a plug-in adapter for around $40-$80. You remove the radio to access the DCM 🎬 See how to safely remove the stereo head unit on a Forester, unplug the vehicle harness from the DCM, and plug the bypass harness in its place. This harness contains wiring that correctly loops back the front speaker and microphone audio signals while leaving the faulty DCM completely disconnected from power. This permanently solves the battery drain and restores all audio functions.
2. Fuse Tap Power Reroute
A cheaper but slightly more complex method involves using an "add-a-circuit" fuse tap to move the DCM's power source. Instead of being connected to a fuse that has power all the time, you reroute it to a fuse that only has power when the ignition is on (like the accessory or cigarette lighter fuse). This physically cuts power to the DCM when the car is off, preventing any drain. The downside is that, like the bypass harness, Starlink remote services will not work when the car is parked.
Cost of Replacement
| Part or Service | Estimated Cost |
|---|---|
| New OEM Module | $650 - $1,000 |
| Used OEM Module | $100 - $300 |
| Shop Labor (Physical Install) | $150 - $300 (1-2 hours) |
| Dealer Programming | $150 - $250 (1-1.5 hours) |
| Total Dealer Replacement (New) | $950 - $1,550+ |
| DIY Bypass Harness | $40 - $80 |
Frequently Asked Questions
Does a replacement Wireless Communication Module need to be programmed?
Yes, absolutely. A replacement DCM must be programmed and registered to your vehicle's VIN by a Subaru dealer. Without this step, the Starlink telematics services will not function.
Can I just pull the DCM fuse to stop the battery drain?
You can, and it will stop the battery drain. However, on the Forester, the front speakers and the hands-free microphone audio are routed through the DCM. Pulling the fuse will disable them, meaning you will have no sound from the front of the car and cannot make Bluetooth calls. A bypass harness is a better solution.
Is there a recall for the DCM battery drain on my 2019-2021 Forester?
As of now, there are no official NHTSA safety recalls for this specific issue. However, Subaru has issued multiple TSBs, extended the part's warranty, and faced class-action lawsuits, indicating they are aware of the problem. Contact your dealer with your VIN to see if your vehicle is covered under the warranty extension program.
Can an independent mechanic or locksmith program a new DCM?
No. This procedure requires Subaru's proprietary diagnostic tool (Subaru Select Monitor) and access to their network to register the module. This is a dealer-only procedure.
Helpful Videos
Technical Specifications
OEM Part Numbers: 86222SJ100 86229SJ000 86229SJ100 86229SJ101
Commonly referred to as the Data Communication Module (DCM). Located behind the infotainment head unit. Integrates cellular (VoLTE) and GPS communication.
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- Subaru Forester:
- 🎬 Helpful Videos
- 🛍️ Shop This Part
- The #1 Problem: Parasitic Battery Drain
- Known Issues, TSBs, and Warranty Extensions
- Symptoms of a Failing Wireless Communication Module
- Diagnosis: Is the DCM Draining Your Battery?
- Buying a Used Wireless Communication Module: Read This First!
- DIY Alternatives to Full Replacement
- 1. Aftermarket Bypass Harness
- 2. Fuse Tap Power Reroute
- Cost of Replacement
- Frequently Asked Questions
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