Common OBD Two Codes

Locking gas cap

One of the most common OBD two codes would be for the evaporative emissions system. These codes were designed by the manufacturer and mandated by clean air laws.

Basically this is that the fuel system on every automobile must be completely sealed. No longer are you allowed to vent fuel vapor into the atmosphere.

This means that a storage and burning system is necessary to properly handle the naturally occurring fuel vaporization process.

Depending on the year make and model of the vehicle the codes set will usually be in the P0400 range. These codes when set will help you determine what the problem with the system may be.

When the fuel vapor system is determined to be leaking the severity of the leak is measured. Individual codes may set for a small leak, a medium-sized leak, or even a large fuel vapor leak.

Also in the P0400 range of codes will be specific codes for the canister and purge valve functions of the evaporation emissions system. All of the failures in the P0400 range could be considered common OBD codes. Again depending on the year make and model of the vehicle. But I have seen failures in all parts of the evap at one time or another.

OBD two evap systems leaks

OBD two monitors the evaporative system by testing the ability of the fuel tank to hold pressure as well as purging the system to vent petroleum fumes from the charcoal canister storage device. The most common way that this pressure test is deployed is with a small pump. Read more