What Error 04 Means

Error 04 on Bafang eBike systems signals that the controller has detected the throttle is not at its zero (resting) position at startup or during operation. The Bafang controller reads throttle position as a voltage from 0.8V to 4.2V. At rest the throttle should output approximately 0.8 to 1.0V. If the controller sees a value above 1.2V at startup or when no throttle input is expected, it raises error 04 and disables motor output as a safety measure — preventing unintended acceleration.

Safety first: Error 04 is a safety mechanism. A throttle stuck in the open position could cause uncontrolled acceleration. Do not bypass or ignore this error — diagnose and fix the underlying cause.

Common Causes

  1. Throttle physically stuck — The throttle sleeve has seized against the grip, or debris is preventing it from returning to the resting position. Common on twist throttles in muddy conditions.
  2. Throttle cable routing too tight — On thumb throttles, routing the cable in a tight bend causes the internal spring to be unable to return the lever to zero.
  3. Damaged or corroded throttle connector — A connector with moisture or corrosion raises the signal voltage above the error threshold.
  4. Failed throttle Hall sensor — The internal Hall sensor in the throttle has drifted or failed, permanently outputting above-zero voltage.
  5. Throttle connector partially unplugged — A half-inserted connector produces an indeterminate voltage that the controller flags as error 04.

Fix Procedure

Step 1: Physical Check

With the bike powered off, operate the throttle through its full range by hand. Release it completely and check it returns fully to rest position with a snap. Any stiffness, sticking, or incomplete return indicates a mechanical throttle fault. Check for debris under twist throttle sleeves, and check that thumb throttle levers move freely.

Step 2: Unplug and Retest

Disconnect the throttle connector from the main harness completely. Power on the bike. If error 04 clears with the throttle disconnected, the throttle unit or its cable is generating the fault voltage — not the controller. This confirms the fault source.

Step 3: Clean the Connector

Inspect the throttle connector for corrosion, bent pins, or moisture. Spray with contact cleaner, dry thoroughly, and reconnect firmly. Many error 04 faults on bikes ridden in rain are resolved by connector cleaning alone.

Step 4: Check Cable Routing

Verify the throttle cable is not routed through any tight bend that could put tension on the lever. Route the cable with a gentle arc, with at least 100 mm of free cable at the handlebar.

Step 5: Replace the Throttle

If the throttle does not return cleanly or error 04 persists after connector cleaning, replace the throttle. Bafang-compatible thumb and twist throttles are available for EUR 10 to EUR 20 and are rider-replaceable — unplug the old connector, route the new cable, and plug in.