Automotive power system is more complicated than general system because of its tough EMC environmental. Many EMI happened during Automotive electrical equipment operation. With much wide bandwidth, these disturbs can be transited to power system by conducting, coupling and radiation. Normal operation of Electronic equipment can be impacted. Some worst disturb could be happened at vehicle system itself like ignition, generator and rectifier. Conducting and coupling disturbs were defined in ISO7637, it is most focused on road vehicle and trailer.  

5 test pulses were defined in ISO7637 for automotive electronic equipment anti-disturb on power.wherein：

Pulse1 is used to simulate transient disturb happened during parallel inductive load power off, like light power off and car horn off.

Pulse2a is used to simulate transient disturb happened during parallel load sudden power off, it is positive disturb with small power and quick speed.

Pulse2b is used to simulate transient disturb happened during ignition power off, DC motor act as generator. It is low speed.

Pulse3a/3b is used to simulate transient disturb happened during relay on and off. It is quick speed, small power small pulses group. 

Pulse4 is used to simulate transient disturb happened during ignition power on, DC voltage drop.

Pulse5 is used to simulate transient disturb happened during load dump which is battery suddenly disconnected with charging DC line.