What a mechanic actually checks first
The controller is where this diagnosis ends, not where it starts. Confirming a dead controller means clearing everything around it first, in order. The battery gets measured at its output contacts, and if the bike will power up at all, checked under load, because a controller cannot be judged on a starved power supply. The main fuse gets pulled and inspected, along with every connector between battery and controller, since a dead bike with a good battery is more often a fuse or a corroded connection than a cooked board.
Only then does the controller bay get opened: a visual inspection for heat discoloration, melted insulation on the phase wires, swollen components, and the smell, because cooked electronics announce themselves. After that come the signal checks: throttle and pedal-assist inputs measured at the controller plugs, and the motor's hall sensors tested through the controller connector. That last step matters, because it separates a controller that has actually failed from one that is being fed bad signals and only looks guilty.
If the controller is condemned, the second half of the job is matching. Voltage, current rating, connector standard, and sensor type all have to agree with the rest of the bike, and on brands with proprietary plugs the options narrow to an OEM unit or a harness-level conversion, which changes the quote.
DIY or call a tech
The honest owner path here is verification, not repair, and it is worth doing because it can end the story cheaply. Confirm the battery is charged, seated, and recognized by its charger. Find and check the main fuse if your bike has an accessible one, near the battery mount or on the pack itself: a blown fuse imitates controller death exactly and is the best possible outcome. With everything powered off, inspect the visible connectors for corrosion and full seating. And write down the history: a burning smell, a death mid-climb on a hot day, or a recent soaking each point the diagnosis before a tech ever arrives.
Past that, this is tech work, squarely. The controller bay involves sealed connections and full pack voltage, a wiring mistake can destroy a replacement controller the moment it powers up, and a mis-specced controller can damage the motor it drives. This is also where our recommendation gets firm about temptation: bolting on an oversized controller to make the bike faster is a known route to exactly the failure this page describes, and we see the results come into the van.
What the repair costs and why
Our network's typical range for this symptom runs $120 to $350. The $120 end covers the cases where the controller survives: harness repair and re-waterproofing after diagnosis finds damaged wiring or corroded connections rather than a dead board. The $350 end is a full controller replacement on a bike where the part is costly or buried deep in the frame. Parts availability moves the number more than labor does, which the brand table below reflects: Rad controllers are plentiful and the swap is routine, so that job lands between $140 and $260 even though controller faults are the signature Rad failure.