BMW fault code 0021
Convertible-top module
In the convertible-top module, code 0021 means different things depending on the version of the module in the car. Find your car below; the app shows the right one for yours.
CVM: Switch, cowl unlocked, voltage undefined
Module version: Convertible-top module (CVM_II)
In: 3 Series (E46) 1998–2006
CVM: Switch, cowl unlocked, input voltage undefined
Module version: Convertible-top module (CVM_III)
In: Z8 (E52) 2000–2003
CVM: Switch, cowl panel unlocked, undefined voltage range
Module version: Convertible-top module (CVM_IV)
In: Z4 (E85) 2002–2008
Reading and clearing it
Fault code 0021 is a BMW code, stored in the car's convertible-top module, not a generic OBD2 code (P0xxx): a generic OBD2 reader only reaches the engine's emissions faults, so it won't show it. AutoLingo for BMW reads it with BMW's own diagnostic protocols, in plain English, with the details the module stored about it, and clears it after a repair. If a fault comes right back after it's cleared, the problem is still there.
The convertible-top module is on: 3 Series (E46), Z8 (E52), Z4 (E85), Z4 (E86)
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