Bosch error code 602 indicates an abnormal discharge condition detected by the Battery Management System (BMS). The BMS continuously monitors current output, individual cell group voltages, and internal pack temperatures during operation. If the battery experiences extreme voltage drop under load, draws excessive amperage, operates outside safe thermal thresholds, or detects high resistance at the discharge terminals, it shuts down power delivery and logs code 602 to protect the lithium-ion cells from thermal breakdown.
Fast Fix
Turn off the e-bike, remove the battery, and let it rest at room temperature (around 65°F–70°F / 18°C–21°C) for thirty minutes if it was exposed to freezing cold or extreme heat. Clean the terminal contacts on the battery and frame cradle, reinstall the pack securely, and connect it to the official Bosch charger until fully charged before riding.
Quick Status & System Safety
- Severity: High. The battery’s integrated protection circuit has actively cut power to prevent permanent cell damage or thermal hazards.
- Riding Safety: The motor will not provide power. Mechanical pedaling is safe, but the battery should not be forced to discharge until the underlying issue is identified.
- Root Cause: Severe cell voltage sag under acceleration, extreme battery temperature during discharge, pitted or corroded discharge pins, or an aging, degraded cell pack.
What Bosch Error Code 602 Means
A Bosch PowerPack or PowerTube contains high-capacity lithium-ion cells arranged in series and parallel. During riding, the drive unit demands varying current (amperage) depending on your assist mode and terrain.
The BMS monitors this discharge on a millisecond basis:
[Drive Unit Demands High Current (Turbo Mode / Steep Hill)]
|
[Current Flows Across Discharge Terminals]
|
Does Voltage Drop Below Critical Threshold,
or Does Pack Temperature Exceed Limits?
/ \
[YES] [NO]
/ \
[BMS Trips Protection] [Normal Operation Continues]
|
[Bosch Error Code 602]
If the voltage of a single cell series drops below its safe minimum while riding, or if total current exceeds design limits, the BMS opens its solid-state switches (MOSFETs) to stop current flow immediately. This prevents the pack from entering deep discharge, which can permanently damage lithium cells.
Diagnostic Path
- When did error 602 appear?
- Under hard acceleration or steep climbing: Points to severe voltage sag from a weak cell group, poor contact fit, or an aging pack. Consult Why Your E-Bike Battery Cuts Out Under Heavy Load.
- Immediately upon powering on in cold or hot weather: Points to temperature-induced discharge protection.
- Directly after hitting a rough bump: Points to physical contact separation or terminal arcing between the battery and cradle.
- What do the battery pack LEDs show?
- If one or more LEDs flash in a specific sequence, the BMS is signaling a hardware-level battery fault.
Likely Causes
- Thermal Out-of-Range Condition: Discharging the battery when its internal temperature is below 14°F (-10°C) or above 140°F (60°C).
- Pitted or Burnt Discharge Terminals: High electrical resistance caused by micro-arcing across loose or dirty battery contact blades, generating heat and triggering safety cutouts.
- Severe Cell Degradation (Voltage Sag): High internal resistance in an old or high-mileage battery pack causing overall pack voltage to collapse under load.
- Loose Battery Rail Adjustment: A loose mounting rail allowing the battery to bounce slightly, breaking contact momentarily while discharging high current.
Step-by-Step Troubleshooting
Step 1: Normalize Battery Temperature
- Remove the battery pack from the bike.
- Bring the battery indoors into a moderate, room-temperature environment.
- Allow the pack to rest for at least 30 to 60 minutes. Lithium battery core temperatures change slowly; even if the outer plastic casing feels warm, internal cells may still be cold.
- Once normalized, press the battery indicator button to verify state of charge.
Step 2: Inspect Battery Discharge Pins and Terminals
- Examine the heavy copper power terminals on the bike’s mounting plate.
- Look for dark black pitting, carbon buildup, or melted plastic around the terminal base.
- If carbon deposits or dirt are visible, clean the metal blades using electrical contact cleaner on a lint-free swab.
- If terminal pins are severely pitted or discolored from heat, contact resistance will continually trip code 602. Learn how to clean and restore these pins in How to Clean Pitted or Burnt Discharge Pins on a Battery Cradle.
Step 3: Check Battery Latch Tightness
A battery that rattles in its mount will break electrical contact under load:
- Reinstall the battery into the frame.
- Push and pull on the pack firmly. There should be zero play between the pack and the mounting interface.
- If the battery rattles or shifts, adjust the mounting bracket screws to increase mechanical clamping tension. For step-by-step rail adjustment, follow Fixing a Loose Battery Tray Causing E-Bike Power Cutouts.
Step 4: Perform a BMS Wake and Charge Cycle
- Plug the battery into its genuine Bosch charger.
- Connect the charger to the wall outlet and allow the battery to reach 100% capacity.
- Keeping the battery on the charger for an extra hour after reaching full charge allows the BMS to run cell-balancing routines. To understand how BMS resets work, read How to Reset an E-Bike Battery BMS.
- Reinstall the fully charged pack on the bike and test ride in a moderate assist mode (Tour or Eco) before trying Turbo.
Signs of Dangerous Battery Failure
Stop using the battery immediately and move it to a fire-safe location if you notice any of the following:
- The battery casing is warm to the touch while sitting idle.
- The casing shows signs of bulging, swelling, or seam cracking.
- There is a persistent chemical, plastic, or ozone smell.
- The battery trips code 602 immediately upon connection, even after a full reset and room-temperature rest.
Commonly Confused Problems
- **Bosch Error Code 606: Battery Management System Fault:** Code 606 reflects an internal electronic component or sensor failure inside the BMS logic board itself, whereas 602 indicates an active discharge protection event triggered by current, voltage, or temperature.
- **Bosch Error Code 610: Battery Overvoltage Fix:** Code 610 triggers when voltage exceeds safe maximum thresholds (typically during charging or aggressive regenerative braking), the opposite of the discharge cutoffs associated with 602.
- **Bosch Error Code 530: Battery Fault Troubleshooting:** Code 530 is an overarching battery communication or recognition fault, while 602 is specific to the power delivery circuit.
Escalation and Replacement
If error code 602 recurs after cleaning terminals, tightening the mount, and balancing the cells, the battery pack has likely reached the end of its functional life. Over time, lithium cells develop high internal resistance; while the pack may show 100% charge at rest, demanding motor power causes the internal voltage to plummet instantly below the BMS cutoff threshold.
Take the battery to an authorized Bosch dealer. The shop can run a diagnostic battery capacity test using the Bosch DiagnosticTool, which outputs:
- Total lifetime charge cycles.
- Maximum delivered capacity vs. original rated capacity.
- Fault logs recording the exact voltage drop that triggered the discharge error.
If the internal cell blocks are degraded or out of balance, the battery pack must be replaced with a genuine Bosch PowerPack or PowerTube. Lithium-ion battery packs should never be repaired or rebuilt by uncertified third parties due to severe thermal runaway risks.