The Bosch Gen4 Motors were introduced in the market in 2020. If the bike is 2020+ and the motor is named Bosch PerformanceLine CX, with a big chainring, it is a Bosch Gen4 motor.

Los motores Bosch Gen4 were introduced to the market in 2020. They were a signficant upgrade over the previous Gen2 motors. The motors have an entirely different internal construction. Unfortunately, with this generation of motors, Bosch introduced several elements that make the repairs of these motors not possible.

They have many names: Bosch SmartSystem PerformanceLine CX, PerformanceLine CX, and CargoLine. They have the following SKUs:
SmartSystem: Bosch BDU3741, BDU3781
System 2: Bosch BDU490P, BDU450CX
Visit our guide to Bosch bicycle motor generations for more information.

Bosch Generation 4 (Bosch Gen 4) motors were introduced to the market in 2020 and have been on the market for several years now. Although they are very powerful and reliable motors, they do have their weaknesses.
One weakness in Bosch Gen 4 motors, which causes the most serious consequence (engine replacement), is the seal between the bottom bracket axles. This seal is not airtight, and if the bearings already have a little play, it allows water to enter between the axles, which can destroy the motor. The axle is coded with the torque sensor and cannot be replaced.
To avoid this situation, at BiciFix we recommend that the motor be checked every year after the first 36 months of purchase and, if there is any play in the main bearings, even if they appear to be fine, they should be replaced to prevent water ingress. In the images you can see the condition of a shaft from a motor with only 5000 km!

Bosch has launched an official maintenance kit that includes the seals covering the main bearings. You can find this kit on our website. The kit comes with an instruction booklet on how to make the change. Be careful, because one of the washers is a little difficult to remove. Unfortunately, our experience shows that this kit is not enough to prevent problems with the motor. There is a seal between the axles that allows water to enter the motor. If water has already entered, the only option is to open the motor, clean it and replace at least the main bearings (to prevent play, which contributes to water ingress).
This motor requires many specific tools and knowledge of its internal construction. We recommend that the repair be carried out by a specialist workshop, such as BiciFix. If you would like to have your Bosch Gen 4 serviced at Bicifix, you can request a ‘Quote’ and send us the motor, with a description of the problems you have noticed.

When we receive the motor, we will connect it to our test bike and check its electronic and software status.
Then, we will open it up and send you photos and information about the condition of the mechanical parts, along with a repair estimate. If you approve it, we will repair the motor, check its condition again on our test bike, and send it to your address.