Thinkpads Forum

I tried repasting my T420 and ended up breaking the Yellow Tachometer wire. The laptop would refuse to go past the “Fan Error” screen despite whatever inputs I gave.

I replaced the fan thrice with exact same model numbers all sourced differently, and still the exact same issue.

Sounds like connector port problem, probably you've broken not just the wire, worth checking the connector port and see if the fan starts at all(most likely not)