CM in automotive stands for a few different things which include configuration management, contract manufacturer or corrective maintenance.
In most cases the CM in automotive would stand for corrective maintenance especially if it's a repair manual or manual about keeping your vehicle in good shape.
Corrective maintenance is a type of maintenance that fixes any problems and restores the equipment or vehicle to working order.
Corrective maintenance can be either planned or unplanned.
Contract manufacturer is a third party manufacturer which makes components or products or parts for a company.
A company might outsource to a CM or contract manufacturer for pricing and for manufacturing of parts, components, products etc.
And configuration management is a management process which ensures that a product's or parts performance and attributes are consistent with it's design and requirements as well as operational information.
And can also be a process to track and control IT resources, applications and services.
CM in automotive can also mean commercial motor vehicle or refer to numbers on an engine such as CM871 which is a dual cam engine that was produced between 2007 and 2009 and is an EPA 2007 engine that is equipped with an EGR system and a DPF.