The Shimano SM-EW90-B [paid link] Junction Box is a critical component of the Di2 electronic shifting system. It acts as the central connection hub, linking the shifters, derailleurs, and the main battery. When installed and configured correctly, it ensures smooth communication across the drivetrain, delivering precise electronic shifting. However, improper setup, cable wear, or firmware inconsistencies can cause several performance issues. This article provides a detailed, step-by-step troubleshooting guide focused exclusively on the Shimano SM-EW90-B [paid link].
Understanding the Role of the SM-EW90-B
The SM-EW90-B serves as the cockpit junction in Shimano Di2 systems. It features three E-Tube ports for connecting shifters and the main wiring harness. In addition, it includes a charging and adjustment port. Any disruption in this unit can affect signal transmission, battery communication, or shifting performance. Understanding its role helps in diagnosing problems quickly and accurately.
Tools Required
- 2mm hex key
- E-Tube cables (for testing or replacement)
- Shimano Di2 charger (SM-BCR2)
- E-Tube Project software (for PC or mobile)
- Multimeter (optional, for voltage checks)
Common Symptoms of SM-EW90-B Problems
When the SM-EW90-B develops issues, several symptoms may appear across the Di2 system:
- Intermittent shifting or delayed response
- No power to shifters or derailleurs
- Battery charge not registering
- LEDs flashing irregularly on the junction box
- Failure to connect to the E-Tube Project software
Recognizing these signs helps narrow down whether the problem lies within the junction box or another connected component.
Step 1: Verify Cable Connections
Start by checking all E-Tube connections leading to the SM-EW90-B. Loose or improperly seated cables are the most common cause of communication failure.
Each port should have the cable fully inserted until an audible or tactile “click” is felt. Pull gently to confirm that it’s locked in place. Examine each plug for debris, corrosion, or bent pins, as these can interrupt the electronic signal.
If connections appear secure, disconnect and reconnect them to ensure a solid electrical interface. It’s essential to use Shimano’s TL-EW02 tool to prevent cable damage during this process.
Step 2: Inspect the E-Tube Cables
E-Tube cables can degrade over time, especially if they are tightly bent or pinched. A damaged cable can cause intermittent disconnections that appear as shifting delays.
Visually inspect cables for sharp bends or fraying at the connectors. If the issue persists after reseating cables, replace one cable at a time to isolate the faulty line. Using a spare known-good cable can quickly confirm whether the problem is cable-related or internal to the SM-EW90-B.
Step 3: Check Power Delivery
If none of the LEDs on the SM-EW90-B illuminate, the issue may be with power delivery from the main battery. Ensure that the battery is charged and properly connected to the system.
Using the Shimano Di2 charger (SM-BCR2), connect it to the junction box’s charging port. If no LEDs activate, try another outlet or USB port to confirm power availability. If the battery is charged but no lights appear, the internal circuits in the junction box may be defective and require replacement.
Step 4: Test with E-Tube Project Software
Shimano’s E-Tube Project is an essential diagnostic tool for electronic systems. Connect the SM-EW90-B via the USB charging port using the Di2 charger cable. The software should automatically detect the junction box and all connected components.
If the SM-EW90-B does not appear, it indicates either a failed internal communication circuit or an incompatible firmware version. Updating firmware across all connected devices often resolves most communication inconsistencies.
Perform a full system check using the software to identify error codes or components that fail to respond. Note any firmware mismatches or devices not recognized, as these are key indicators of system-level [paid link] faults.
Step 5: Diagnose LED Indicators
The SM-EW90-B features LED lights that provide quick feedback on system status.
- Solid Red LED: Battery low or nearly depleted
- Flashing Red LED: Communication error or short circuit
- Solid Green LED: System active and functional
- Flashing Green LED: System in adjustment mode
If the red LED continues flashing after all connections are verified, it may suggest an internal short or a damaged circuit board. In that case, the junction box should be replaced, as internal repairs are not serviceable.
Step 6: Reset and Recalibrate the System
Sometimes, after firmware updates or component replacements, recalibration is required. Press and hold the button on the SM-EW90-B for about five seconds until the LEDs flash alternately. This resets the system and reinitializes communication between components.
After resetting, use the E-Tube Project to confirm that all connected parts are detected and functional. If communication is restored, perform a test shift sequence to ensure reliability under load.
Step 7: Environmental and Mounting Considerations
Moisture and vibration can lead to intermittent SM-EW90-B performance issues. The junction box should be securely mounted under the stem using Shimano’s bracket or integrated handlebar system.
Avoid over-tightening zip ties or clamps, as excessive pressure may deform the housing and affect port alignment. Clean the unit regularly with a soft cloth and ensure that all port covers are closed to prevent water ingress during wet rides.
Step 8: When Replacement Is Necessary
If the SM-EW90-B consistently fails to communicate, does not light up even with verified power, or cannot be recognized by the E-Tube software, replacement is the best course of action.
This component is not user-serviceable, and internal diagnostics are not available beyond LED and software testing. Always replace with the same model (SM-EW90-B) to maintain system compatibility with existing E-Tube wiring and Di2 components.
Optimizing SM-EW90-B Performance
To maintain optimal performance, periodically inspect cables, update firmware, and clean connectors. Using Shimano’s official E-Tube software ensures compatibility between generations of Di2 components.
Regular system checks help prevent unexpected shifting failures, particularly before long rides or races. Riders should also avoid mixing cables from non-Shimano sources, as resistance variations can disrupt signal integrity within the SM-EW90-B junction.
Preventive Maintenance Tips
- Inspect and clean ports every 3–6 months.
- Update firmware through E-Tube Project twice yearly.
- Store the bike in a dry environment to avoid condensation buildup.
- Ensure cables have smooth routing with no sharp bends.
A consistent preventive routine greatly reduces the chance of mid-ride communication errors or power loss.
Final Thoughts
The Shimano SM-EW90-B is a highly reliable junction box when installed and maintained correctly. Most operational issues stem from simple connection faults or firmware inconsistencies rather than internal defects. Through careful inspection, cable testing, and software diagnostics, nearly all problems can be resolved without component replacement. Regular maintenance and attention to detail ensure that your Di2 system remains precise, responsive, and race-ready for years.