Applies to: S3 / X3 · Sources: Mike Coats, Reddit r/VanMoofSelfRepair, YouTube (RAZ), iFixit
Overview
The S3/X3 uses a 36V cylindrical lithium-ion battery pack built from LG INR18650 MJ1 cells arranged in 10 groups of 4 cells each (10S4P). The pack lives inside the down tube and is managed by a proprietary BMS (Battery Management System). The BMS monitors voltage, temperature, and current — and will lock out charging or discharging if it detects a fault.
The most common failures are: (1) deep discharge lockout — the bike sat unused and the cells dropped below the BMS safety threshold; (2) a blown SMD fuse on the BMS PCB — triggered by an overcurrent event or cell imbalance. Both are repairable.
Symptoms & Error Codes
| Error |
Meaning |
Likely Cause |
| Err 6 | Battery voltage too low | Deep discharge / blown BMS fuse |
| Err 17 | Motor controller comms fault | Usually secondary to Err 6 — BMS not supplying power |
| Err 19 | Battery temperature sensor fault | BMS lockout or sensor wire damage |
| Err 20 | Charging fault | BMS not accepting charge — blown fuse or deep discharge |
| Err 21 | Overvoltage protection | Stop charging immediately; BMS triggered protection |
| No errors, won't charge | Charger light stays green | BMS locked out due to deep discharge |
Note: Errors 6, 17, 19 and 20 appearing together almost always point to a blown BMS fuse or deep discharge. Start diagnosis there.
Repair 1 — Deep Discharge Recovery (No Disassembly)
Difficulty: Intermediate · Time: 30–60 min · Sources: Reddit r/VanMoofSelfRepair, YouTube RAZ
When to use: Bike sat unused for months. Charger light stays green (not red). Errors 6/17/19/20. The BMS has shut down because cells dropped below ~2.5V/cell.
What you need
Bench power supply (0–60V, min 2A) — e.g. Korad KA3005P
Multimeter
Banana-to-DC cables with correct polarity
VanMoof battery connector pinout (see below)
Battery Connector Pinout (S3/X3)
Charge port (green connector on BMS board):
· Pin 3 (CH−) = Charge negative
· Pin 4 (CH+) = Charge positive
Discharge port (red connector):
· Pin 1 (DSG−) = Discharge negative
· Pin 2 (DSG+) = Discharge positive
Steps — Method A: Via Discharge Ports (Recommended by community)
1
Remove the battery from the bike: undo 3 security torx bolts on the bottom of the down tube, remove the protective cap, pull battery out using the swing handle. Disconnect the cadence sensor cable carefully.
2
Measure pack voltage across the discharge ports (DSG+ and DSG−) with your multimeter. A healthy pack reads 36–42V. Deep-discharged packs often read below 30V or even 0V.
3
Set bench PSU to 42V, limit current to 0.5–1A. Connect positive to DSG+, negative to DSG−. The PSU will push current directly into the cells, bypassing the BMS lockout.
4
Monitor voltage as it rises. Once it reaches ~36V, the BMS should wake up. This can take 10–30 minutes depending on how discharged the cells are.
5
Disconnect PSU and try charging normally with the VanMoof charger. The charger light should now turn red (charging). If it stays green, try Method B.
Method B: Via Charge Ports
1
Set PSU to 42V, 0.8A. Connect to CH+ (pin 4) and CH− (pin 3) on the BMS charge connector.
2
Some community members report needing to connect all battery cables (not just the charge pins) for the BMS to respond. Try connecting the full harness if CH-only doesn't work.
3
Wait 15–30 min. Voltage should climb. Once above 36V, try normal charging.
Community tip (RAZ, YouTube): The "hard reset" method — connecting a PSU directly to the discharge pins — is the most reliable. Multiple community members confirmed success after the bike sat for 6–12 months.
Repair 2 — BMS Fuse Replacement
Difficulty: Advanced (requires SMD soldering) · Time: 2–4 hours · Sources: Reddit r/vanmoofbicycle (74 upvotes, 84 comments)
When to use: Errors 6/17/19/20 persist after trying deep discharge recovery. Multimeter shows no continuity across the fuse on the BMS board. This is the #1 reported fix — a €3 SMD fuse is the culprit in most cases.
The Fuse
Part number: SFK-4045A (also listed as SFK-4045, 45AK10A, or SFK 4045)
Rating: 45A self-resetting protection fuse
Price: ~€3/piece on AliExpress (order 5 — delivery ~10 days from China)
Also available: razspareparts.com (UK), heskon.de (Germany)
Alternative: SFK-1445 (used in older BMS revisions)
What you need
SMD soldering iron + fine tip (or hot air station)
SFK-4045A fuse (order from AliExpress)
Multimeter with continuity mode
Security Torx T10 screwdriver
Phillips head screwdriver
iFixit opening tool or plastic pry tool
Bench PSU (for post-repair verification)
Solder wick / desoldering pump
Steps
1
Remove battery from bike (see Step 1 in Repair 1 above).
2
Open the battery pack: remove 5 cross-head screws from each end cap. Use an opening tool to pop the caps off. The cap with the swing handle comes off fully; the cap with the power connector stays wired in.
3
Slide out the cell assembly by pressing firmly from the open end. The whole pack of cells + PCB slides out.
4
Locate the BMS PCB. Find the SMD fuse — it is a small rectangular component. Test with multimeter in continuity mode. A blown fuse shows no continuity (open circuit).
5
Check cell voltages before replacing the fuse. Measure each group of 4 cells using the balance wire connector. All groups should read within ~0.1V of each other (~3.5–4.2V per group). If one group is significantly lower, balance or charge that group first — an imbalanced pack will blow the new fuse instantly.
6
Desolder the blown fuse with hot air or a fine soldering iron. Clean the pads with solder wick.
7
Solder the new SFK-4045A in place. Check continuity — you should now have a complete circuit.
8
Reassemble the pack in reverse order. Slide cells back in, reattach end caps, replace screws.
9
Test: connect bench PSU at 42V/1A to discharge ports. Voltage should rise and BMS should accept charge. Then try normal VanMoof charger — light should go red.
Why fuses blow instantly after replacement: Cell imbalance. If one cell group has significantly different voltage, the BMS triggers the fuse as soon as it's live. Balance all cell groups before installing the new fuse.
Community result (74 upvotes): "After a long time waiting for parts and tools I am very happy to tell you, I fixed a S3 battery which wouldn't charge and showed Error 6, 17, 19 and 20. The problematic part was a little SMD fuse, which is 3 Euros a piece."
Repair 3 — Individual Cell Group Charging
Difficulty: Expert · Time: 4–8 hours · Source: Mike Coats Blog Part 2
When to use: BMS fuse replacement didn't work, or one cell group is deeply discharged and won't recover. Requires opening the cell assembly.
1
Open battery pack as in Repair 2, steps 1–3.
2
Carefully unwrap the glass-fibre tape around the cell assembly. This reveals the 10 cell groups and two embedded temperature sensors.
3
Locate voltage sense wires — there are connections every 1/10 of the pack length (one per cell group). These let you measure sub-voltages per group.
4
Charge each low group individually. The LG MJ1 cells charge at: CC 1.7A → CV 4.2V per cell. Each group of 4 cells: charge at ~6.8A CC → 16.8V CV. Use a PSU with CC/CV mode.
5
Once all groups are within 0.05V of each other, reassemble the pack (re-wrap with tape, slide back in, close end caps).
6
The BMS should now wake up and accept a normal charge via the VanMoof charger.
Cell spec: LG INR18650 MJ1 (partial code R18650MJ1 visible on cells). Standard 18650 Li-ion — max charge 4.2V/cell, min safe voltage ~2.5V/cell.
Repair 3 — Restarting / Resetting the BMS
Difficulty: Intermediate · Sources: Reddit r/vanmoofbicycle (BMS repair thread), YouTube RAZ
The BMS can get stuck in a locked or "sleeping" state in two scenarios: (1) deep discharge lockout, or (2) after a fuse replacement where the BMS retains an error state in memory even though the fuse is now good. Two methods exist to wake it.
Method A — 42V on Charge Ports for 13 Seconds (quickest first attempt)
When to use: BMS is locked out — errors 6/17/19/20, charger light stays green, or bike won't respond after deep discharge. Try this first before any disassembly.
1
Remove the battery from the bike (3 security torx bolts on the down tube bottom, pull out using the swing handle).
2
Set bench PSU to 42V / 0.5–1A. Connect positive to CH+ (pin 4, green connector) and negative to CH− (pin 3, green connector).
3
Hold for 13 seconds. This brief pulse at 42V is reported by the community to wake a sleeping BMS and clear its locked state. The PSU may show near-zero current draw — that is normal; the BMS is not yet accepting charge, just being signalled.
4
Disconnect PSU and try the VanMoof charger normally. The charger light should now turn red (charging).
Note: The 42V / charge ports method is confirmed in multiple community sources. The 13-second hold time is reported by owners who successfully revived their battery this way. It corresponds to the time the BMS needs to re-initialise its protection circuits after being woken by an external voltage signal.
Method A2 — Discharge + Apply to Charge Ports (if Method A alone fails)
When to use: Fuse was replaced but BMS still holds old error state in memory. Battery charges via discharge ports but not via BMS charge ports.
1
Discharge the battery pack through the discharge ports using a resistive load — community-confirmed method: 3× 12V car headlight bulbs wired in series. Any load pulling a few amps works. Stop when pack drops to ~32–34V (do not go below 30V / ~3.0V per cell group).
2
Apply 42V for 13 seconds to CH+ / CH− as described in Method A above.
3
Try normal charging. Charger light should go red.
Community confirmation (5 upvotes): "It appears as though if the fuse is replaced but the battery is still fully charged then the BMS holds some memory and the errors continue. The solution was to discharge the battery using 3 12V car headlights wired in series, then the BMS reset itself."
Method B — Hardware Reset (VP + Balance Connector)
When to use: After fuse replacement, BMS still shows errors and Method A did not help. This procedure was documented in the community and later deleted — restored by community members.
1
Open the battery pack (see Repair 2, steps 1–3).
2
Disconnect the VP cable — this is the main voltage protection wire connected to the BMS board.
3
Disconnect the cell balancing connector — the wire harness that connects to each individual cell group. This fully de-energises the BMS.
4
Wait 30 seconds for any residual charge in BMS capacitors to discharge.
5
Reconnect the VP wire, then the balance connector. This forces the BMS to re-initialise from scratch.
6
Reassemble pack and test. Try charging via VanMoof charger.
Note: Never disconnect the balance connector while the BMS is live under load — do this only when the pack is at rest and the bike is disconnected. Pulling the balance cable while live can itself blow the fuse.
Method C — GND-RST Reset (via the bike, not the battery)
Some community members mention a "GND-RST reset" performed at the bike level (not the battery). This involves briefly shorting the RST pin to ground on the main connector while the battery is connected. Community reports are mixed — it did not resolve battery fuse faults in most cases, but may help with soft errors.