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Curtis Code 18
Severe Overvoltage — controllers 1234 / 1236 / 1238

Possible causes (from the Curtis manual)

1. See Monitor menu » Battery: Capacitor Voltage. 2. Battery menu parameters are misadjusted. 3. Battery resistance too high for given regen current. 4. Battery disconnected while regen braking.

When it sets / how it clears

Set: Capacitor bank voltage exceeded the Severe Overvoltage limit (see page 55) with FET bridge enabled. Clear: Bring capacitor voltage below Severe Overvoltage limit, and then cycle KSI.

Effect of the fault

ShutdownMotor; ShutdownMainContactor; ShutdownEMBrake; ShutdownThrottle; FullBrake; ShutdownPump.

Curtis 1234/1236/1238 controllers are fitted to many electric forklifts and industrial trucks (including models from Chinese brands that use Curtis control). If your display shows code 18 with a Curtis controller, this entry applies; the vehicle maker’s manual may add model-specific notes.

Need the part?

For controller, contactor, sensor or throttle parts, send us the code (Curtis 18), controller model and vehicle model on WhatsApp — we quote genuine and OEM parts for export.

Source: Curtis 1234/36/38 Controller Manual, OS 11, Section 8 Diagnostics & Troubleshooting, Table 5. Compiled 2026-10-29. No affiliation with Curtis Instruments.