Electrical faults and error codes on e-mountain bikes: How to find the cause

​Our conclusion

Error codes on e-mountain bikes provide important diagnostic information, but they do not automatically spell the end for the motor. Bosch and Shimano list numerous specific codes, whilst DJI, SRAM, Yamaha and Specialized rely more heavily on plain-text messages, apps and dealer diagnostics. You can check the restart function, battery fit, temperature, sensors and firmware yourself. However, in the event of faults with the battery, motor, cables or internal sensors, you’ll need to take it to a specialist workshop.

An e-mountain bike may reduce or completely switch off the motor assistance for a number of reasons. Sometimes it is simply because the battery is too cold, the speed sensor is dirty or a connector is not properly connected. In other cases, there is a fault in the motor control system, the battery management system or the internal wiring.

An error code simply means, at first, that the system has detected an anomaly. It does not automatically mean that the motor is beyond repair. Modern drive systems monitor, amongst other things, voltage, current, temperature, speed, torque, cadence and communication between the individual components.

Many simple problems can be sorted out by yourself. However, in the case of damaged batteries, faulty wiring harnesses, internal engine faults or recurring shutdowns, the matter should be referred to a specialist workshop.

The seven steps of troubleshooting

1. Take a photo of the error code

Make a note of the full code and the exact wording of the error message. Take a photo of the display before you restart the system or clear the error. If the bike needs to go to the workshop later, the mechanics will rely on the information you provide to troubleshoot the problem. You should therefore make notes on the following points:

• Did the fault occur when you started the engine or whilst driving?
• Is the support still working to some extent?
• Is the battery being recognised?
• Can the battery still be charged?
• Had the bike been wet, very hot or very cold beforehand?
• Did the error occur after an update, a repair or a crash?
• Does the error message reappear under heavy load?

2. Restart the system completely

Switch off the e-mountain bike, wait for about 30 seconds, and then restart it. Restarting the bike can resolve a one-off communication error. However, if the error code reappears immediately or after a few metres, you shouldn’t simply keep clearing it.

3. Check the battery and temperature

Check that the battery is fully inserted and locked into place. You may check the external contacts for dirt or moisture. They must be dry before reinserting the battery. Many systems reduce performance in extreme heat, cold or when the battery is very low. Charge the battery at room temperature using the original charger. You must not continue to use or charge a damaged or unusually hot battery.

4. Check the speed sensor and magnet

A speed sensor that has come loose or is dirty may prevent the motor from providing assistance. Check the following possible causes:

• Position of the spoke magnet or sensor ring
• Distance between the magnet and the sensor
• Sludge, metal shavings or other contaminants
• Damage to the sensor and its mounting bracket
• Visible damage to the sensor cable

5. Check visible plug connections

Visible connectors should be carefully checked to ensure they are securely fitted and to check for moisture and external damage. You should not pull out cables that are routed deep within the frame. Damaged cables should be taken to a specialist workshop.

6. Check the app and firmware

Update the relevant smartphone app and check whether firmware updates are available for the motor, battery, display and control unit.

At Bosch, all relevant components must be taken into account together. These include, amongst others, the drive unit, display, control unit, battery, range extender, ABS and ConnectModule. If a component is missing during the update, the system may subsequently function with limitations.

7. Document errors

If the fault persists, make a note of the code, battery level, temperature and the circumstances. The garage should then carry out a full diagnostic check.

Bosch Performance Line CX Gen5 Smart System

The Bosch motor is by far the most commonly fitted motor on e-mountain bikes. The system is regarded as reliable, and the diagnostic options in the event of problems are quite straightforward. With the Performance Line CX featuring the Smart System, error codes are displayed on the screen and via the eBike Flow app. Bosch provides a dedicated online search function for many codes, complete with descriptions and troubleshooting steps.

Important Bosch fault codes

The code 504 Indicates a faulty speed signal. Bosch recommends checking the position of the magnet. Tampering or tuning may also trigger this message. In this case, the assistance is reduced.

The code 650001 This means that the battery itself has detected a fault. Bosch recommends checking the battery mount and the electrical contacts. Corroded contacts may be cleaned carefully with a soft, slightly damp cloth. They must then be left to dry completely.

At 500 and 503015 You will soon reach the limits of what you can do yourself. It is possible to restart the system. If the fault reoccurs, it is likely to be caused by an internal fault in the drive unit or its control system. Bosch describes code 503015 as a fault that can lead to an automatic shutdown and a loss of motor assistance.

Errors following a software update

If the motor stops working immediately after an update, a component may be missing or may not have been fully updated. Check the software version of all components in the eBike Flow app. If not all components are connected, a Bosch specialist dealer should carry out a full update. We do not recommend resetting the system to an older firmware version yourself.

Shimano Steps EP801, Generation 2

The Shimano Steps EP801 uses various error and warning codes. The exact display depends on the screen, the version of the E-TUBE app and the connected components.

Important Shimano codes

Shimano describes E01010, E01011, E01020 to E01022 and E01030 such as sensor faults or sensor deviations in the drive unit. In such cases, no support is provided. The official procedure is to contact the dealer or distributor.

The code E02000 Indicates a communication fault between the battery and the motor. Shimano recommends checking the cable between the drive unit and the battery, as well as the power supply. As these cables are routed through the frame on many e-mountain bikes, further checks should be carried out by a specialist workshop.

At E021 Although the system recognises a battery that generally complies with the standards, it classifies it as incompatible. You can try switching the device off and on again using the battery button. If the error code persists, the battery, firmware or system configuration may be the cause.

The warning notice W013 is relatively harmless. Shimano explains that pressure was detected on a pedal when the bike was switched on, which meant the sensor could not be calibrated correctly. Switch the bike off, take your feet off the pedals and switch it on again. The fault occurs on older E8000 models, but no longer on the new EP801.

The code E013 In certain Shimano systems, this indicates a firmware error. Shimano points out that the error status may persist and that support may be disabled. The firmware can be restored using the relevant dealer or service software.

Avinox M2

For the Avinox M2, there is no publicly available, model-agnostic fault code table comparable to the Bosch codes. Instead, Avinox uses warning messages on the display, the ‘System Status’ menu option and fault logs in the Avinox Ride app.

How to read Avinox error messages

If the drive system detects a fault, a warning will appear on your touchscreen. Swipe up, open the settings and select ‘System status’. The warning details and the recommended steps to resolve the issue will be displayed there.

In the event of a system crash or a recurring error, you can export an error log via the Support section in the Avinox Ride app. This log can then be sent to the bike manufacturer or DJI Support.

What you can check yourself

• Insert the battery correctly and check the charge level
• Restart the system completely
• Check the Bluetooth connection to the app
• Update the app and firmware
• Bringing a bicycle back to normal temperature in extreme heat or cold
• Take a photo of the warning message and the system status
• Export the error log from the app

Avinox points out that the drive system must not be dismantled or modified without authorisation. In the event of an internal motor fault, battery damage or a failed firmware update, the bicycle manufacturer or an authorised service centre must be contacted for assistance.

​SRAM Eagle Powertrain

With the SRAM Eagle Powertrain, many errors are not displayed as traditional numerical codes, but as plain-text messages on the display or in the SRAM AXS app. This is why the exact wording of the message is particularly important.

Relevant SRAM announcements and notices

SRAM states that a flashing yellow LED indicates that a firmware update has failed or been interrupted. The firmware of the affected component can be restored using the SRAM AXS app.

According to SRAM, a red flashing LED on the charger indicates a charger fault. The charging port, the battery and the visible connectors should be checked externally. If the problem persists, contact the SRAM service centre.

If the motor runs initially but the assistance cuts out after a few metres, SRAM cites connection problems with cables and connectors as the most likely cause. You should therefore check the visible areas without removing any cables from the frame.

A dirty speed sensor or sensor ring can also be a factor. SRAM recommends keeping these components clean, as dirt can impair speed detection and, consequently, motor control.

Weak support

In the AXS app, you can check the maximum power and the level of assistance. However, do not change the settings if a battery, motor or communication error is displayed at the same time. Weak assistance does not necessarily indicate a motor fault. Possible causes include:

• Support levels in the AXS app are too low
• Low battery level
• Operating temperature too high or too low
• Irregular foot pressure
• Out-of-date firmware
• Lack of communication or faulty communication between the components

Battery and charging problems

If your e-mountain bike won’t start or the display remains blank, you should first disconnect the charger from the bike. SRAM also cites a flat battery, unusual battery behaviour and connection issues as possible causes. Caution: A damaged battery must not be recharged.

If an error occurs during the charging process, the following applies:

1. Disconnect the charger from the mains
2. Check the charging socket and plug externally
3. Allow the battery to return to normal temperature
4. Reconnect the charger
5. Keep an eye on the charge indicator
6. If the error occurs again, cancel the charging process

Yamaha PW-X3 and PW-X4

At Yamaha, the situation is slightly different from that at Bosch or Shimano. Yamaha provides the latest fault codes and technical information primarily via its dealer and diagnostics portal. The Yamaha diagnostics tool can read out faults, generate repair reports and access the latest technical data.

What you can check yourself

• Is the battery correctly seated in its holder?
• Is the battery sufficiently charged?
• Are the display and control unit switched on?
• Is the speed sensor clean?
• Is the spoke magnet fitted correctly?
• Are any visible cables and plugs dry?
• Is the bike very hot or has it cooled down considerably?
• Is there any indication that an update is required?

It’s also a good idea to restart the system. If the error reappears after the restart, you shouldn’t try to permanently suppress the code by repeatedly switching the system on and off.

Yamaha diagnostics in the workshop

The official Yamaha service portal gives dealers access to the latest fault codes, technical data, repair information and diagnostic reports. This enables the workshop to determine whether the fault is caused by the engine, battery, sensor, display or wiring harness.

A workshop is particularly necessary when:

• The motor is no longer providing any assistance
• The error recurs under load
• The battery is not charged or is not being recognised
• The display restarts several times
• A cable is damaged
• The fault occurs following a fall or water ingress

Pinion MGU

The Pinion MGU combines an electric motor and a gearbox in a single motor-gearbox unit. Consequently, faults can affect both the motor assistance and the electrical control system.

Relevant Pinion fault codes

Pinion calls 4D03 as a reminder to take the weight off the pedals when using the push assist. When 4D08 The gearbox must be recalibrated. The bike must be stationary, and no pressure must be applied to the pedals during calibration. The code 52-02 also indicates that calibration is required. In the case of 4D-01 You should first check the firmware version. Pinion has already released a firmware update to rectify this gear-shifting fault.

When reporting Motor overtemperature The system reduces the assistance level to protect the motor. In this case, switch to a lower assistance level and allow the bike to cool down. If the message appears even under moderate load, or if it occurs repeatedly, there may be a technical fault. In that case, a workshop diagnosis is required.

Battery Saver Mode

In the Battery protection mode Assistance may be reduced due to a very low charge level or an unfavourable temperature. Bring the bike up to a normal temperature and charge the battery using the charger provided. A battery that repeatedly switches to protection mode despite having a sufficient temperature and charge level should be checked by a specialist dealer.

Authorised dealers for the Pinion MGU

The MGU must not be opened. In the event of recurring calibration failures, a blocked circuit, unusual internal noises or a motor or battery fault, the specialist dealer must carry out the diagnosis. Pinion designates the specialist dealer as the first point of contact. The specialist dealer can diagnose the system using the FIT Maintenance Tool and update it if necessary.

Specialized 3.1

With the Specialized Turbo System featuring the 3.1 motor, faults are diagnosed via the display and the Specialized app. A standardised, publicly available list of fault codes for all bikes fitted with the Specialized 3.1 motor is not currently available.

Relevant Specialized news items

What you can check yourself

• Insert the battery correctly
• Check the charge level
• Switch the bike off completely
• Check the speed sensor and magnet
• Check visible plugs for moisture
• Update the app and firmware
• Take a photo of the error message
• Save the event log in the app

If there is a fault following a fall or water ingress, you should not continue riding the bike.

Workshop diagnostics

The message remains No engine or Motor Error If these symptoms persist, the diagnosis must be carried out at a specialist workshop. There, event logs and system components can be analysed. A specialist workshop is required if:

• The motor is not recognised after a restart
• Switches off the assistance whilst driving
• The battery is not being recognised
• The display remains blank
• The error occurs after an update
• The cable, plug or battery is damaged
• The message reappears after calibration

All e-bike motors: Never do this!

Regardless of the engine manufacturer, there are clear limits. You should not carry out the following yourself:

• Opening the battery or replacing individual cells
• Dismantling the engine or gearbox
• Measuring high-voltage contacts
• Repairing damaged cables within the frame
• Bypass safety cut-outs
• Tampering with the speed sensor or speed limit
• Installing unauthorised firmware
• Clearing fault codes by bypassing fuses

Deleting an error log does not fix the underlying cause. It may even make it more difficult to identify the original error later on.

How to prepare for a visit to the garage

If possible, bring the entire bike to the workshop, including the battery, charger, display, range extender and any relevant control units. Please also make a note of:

• Exact error code or wording
• Timing and frequency
• Battery level
• Outside temperature
• Latest firmware update
• A previous fall or contact with water
• Occurs only under heavy loads or even when stationary
• Simultaneous failures of the motor, display or circuitry

A photo of the error code and a short video of any unusual noises can help with the diagnosis.