The Positive Crankcase Ventilation (PCV) system and other components that affect emissions, but do not turn on the Check Engine lamp if there is a malfunction, are required by the Air Resource Board (ARB) to have tamper-proof fasteners to prevent removal or modification.
During service, the fasteners are destroyed if they must be removed, and new tamper-proof fasteners must be installed.

Tamper-proof fasteners can be found on 2016-2018 GM models equipped with the following engines:

4L Gas engine (RPO LE2, LV7)
5L Gas engine (RPO LFV, L3A, L3G)
0L Gas engine (RPO LTG)
6L Duramax diesel engine (RPO LGH, LML, L5P)

Tamper-Proof Drive Bits

The GR-6 bits in the Tamper-Proof Drive Bit Set (EN-50956-A) will install a fastener only, making it ARB compliant.
The set includes three tamper-proof bits, and replaces the single bit (EN-50956) previously released.

The tamper-proof fasteners were originally used only on diesel engines, but gasoline applications have been added recently.
The tamper-proof fasteners are used to attach various emission-related components, such as the oil separator to the valve cover, the oil drain pipe to the front cover on diesel engines, and components in the intake and PCV systems on gasoline engines.

Service Examples

An example of where tamper-proof fasteners are used is the air cleaner outlet duct on a 2017 Spark equipped with the 1.4L gas engine (RPO LV7).
The Service Information instructs to remove the air cleaner outlet duct by using a suitable tool to cut a slot in the tamper-resistant PCV bolt heads (1) and remove them with a flat-bladed tool. Discard the bolts after removal. Installing a new air cleaner outlet duct with the PCV tube and valves to the engine requires using the EN-50956 tamper-proof drive bit.

On 6.6L Duramax diesel engines, a tamper-proof fastener can be found on the PCV oil separator.