Cabin and \textmu

The encoding file cbn_cgvdav.enc is faulty. It used /mu but a look in the pdf shows that the name of the glyph is /uni00B5.

That's why pdflatex complains

pdfTeX warning: pdflatex.exe (file c:/texlive/2016/texmf-dist/fonts/type1/impal
lari/cabin/Cabin-Regular.pfb): glyph `mu' undefined

You should notify the author. http://www.ctan.org/pkg/cabin

As a work-around you can make a local copy of cbn_cgvdav.enc and exchange the two line below the %B0 with these lines here

%B0
  /degree /plusminus /uni00B2 /uni00B3 /.notdef /uni00B5 /paragraph /periodcentered
  /.notdef /uni00B9 /ordmasculine /.notdef /onequarter /onehalf /threequarters /Euro

Update

With the release of 2017-04-02, the pfb files for the Cabin fonts have been fixed and the output of

\documentclass{article}

\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{textcomp}
\usepackage[sfdefault]{cabin}

\begin{document}

\textmu{}µm

\end{document}

is as expected

Original answer

I tried compiling nfssfont with the following interactive session:

> pdflatex nfssfont
This is pdfTeX, Version 3.14159265-2.6-1.40.17 (TeX Live 2016) (preloaded format=pdflatex)
 restricted \write18 enabled.
entering extended mode
(/usr/local/texlive/2016/texmf-dist/tex/latex/base/nfssfont.tex
LaTeX2e <2017/01/01> patch level 3
Babel <3.9r> and hyphenation patterns for 83 language(s) loaded.
(/usr/local/texlive/2016/texmf-dist/tex/latex/base/article.cls
Document Class: article 2014/09/29 v1.4h Standard LaTeX document class
(/usr/local/texlive/2016/texmf-dist/tex/latex/base/size10.clo))
No auxiliary output files.

**********************************************
* NFSS font test program version <v2.2d>
*
* Follow the instructions
**********************************************

Input external font name, e.g., cmr10
(or <enter> for NFSS classification of font):

\currfontname=


*** NFSS classification ***

Font encoding [T1]:

\encoding=TS1
(/usr/local/texlive/2016/texmf-dist/tex/latex/base/ts1enc.def)
Font family [cmr]:

\family=Cabin-TLF
Font series [m]:

\series=
Font shape [n]:

\shape=
Font size [10pt]:

\size=
(/usr/local/texlive/2016/texmf-dist/tex/latex/cabin/TS1Cabin-TLF.fd)
Now type a test command (\help for help):)
*\table\bye
[1{/usr/local/texlive/2016/texmf-var/fonts/map/pdftex/updmap/pdftex.map}]{/usr/
local/texlive/2016/texmf-dist/fonts/enc/dvips/cabin/cbn_cgvdav.enc}</usr/local/
texlive/2016/texmf-dist/fonts/type1/impallari/cabin/Cabin-Regular.pfb

pdfTeX warning: pdflatex (file /usr/local/texlive/2016/texmf-dist/fonts/type1/i
mpallari/cabin/Cabin-Regular.pfb): glyph `mu' undefined


pdfTeX warning: pdflatex (file /usr/local/texlive/2016/texmf-dist/fonts/type1/i
mpallari/cabin/Cabin-Regular.pfb): glyph `onesuperior' undefined


pdfTeX warning: pdflatex (file /usr/local/texlive/2016/texmf-dist/fonts/type1/i
mpallari/cabin/Cabin-Regular.pfb): glyph `threesuperior' undefined


pdfTeX warning: pdflatex (file /usr/local/texlive/2016/texmf-dist/fonts/type1/i
mpallari/cabin/Cabin-Regular.pfb): glyph `twosuperior' undefined
></usr/local/texlive/2016/texmf-dist/fonts/type1/public/amsfonts/cm/cmr10.pfb><
/usr/local/texlive/2016/texmf-dist/fonts/type1/public/amsfonts/cm/cmr7.pfb></us
r/local/texlive/2016/texmf-dist/fonts/type1/public/amsfonts/cm/cmti10.pfb></usr
/local/texlive/2016/texmf-dist/fonts/type1/public/amsfonts/cm/cmtt10.pfb>
Output written on nfssfont.pdf (1 page, 52627 bytes).
Transcript written on nfssfont.log.

If I try the same with cmr, the relevant row in the output is

so the mu should be in slot "B5. However the corresponding row with Cabin-TLF has

according to the warning issued during processing.

The row with CabinCondensed-TLF shows

It's apparent that something went wrong when building the Cabin-Regular.pfb file.

You should file a bug report to Bob Tennent. For the time being, you can obviate by using the condensed version:

\documentclass{article}

\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{textcomp}
\usepackage[sfdefault]{cabin}

\makeatletter
\DeclareRobustCommand{\textmu}{%
  {\usefont{TS1}{CabinCondensed-TLF}{\f@series}{\f@shape}\symbol{"B5}}%
}
\makeatother

\begin{document}

\textmu{}µm

\end{document}

The author of the cabin package, Bob Tennent, sent to me a corrected version of the faulty file Cabin-Regular.pfb. (See egreg's answer).

I have uploaded the corrected file here: http://www.wikiupload.com/HWPLWMIV5RG3QJ5.