System Description

Fuel is filled through the fuel filler pipe and passes through a non-return valve to the tank. The fuel filler pipe acts as an ejector. The fuel flowing down will be accompanied by air from outside and prevent the emission of the fuel vapor into the atmosphere via the opening in the filler pipe. The fuel being filled forces out the gaseous hydrocarbons and the accompanying air through the float valve and on to the evaporative emission canister. The EVAP canister absorbs the hydrocarbons and the air is passed through the shut-off valve (absent on ORVR without tank integrity diagnosis).

At a certain level (approx. 95%), the float valve closes and the pressure in the tank increases. The fuel now rises in the filler pipe and the fuel nozzle closes when the fuel reaches it. The non-return valve in the filler pipe prevents "back-spit" when the nozzle closes.

The pressure remaining in the tank passes slowly through the rollover valve and into the evaporative emission canister. As the fuel level decreases, the fuel runs in from the filler pipe until it is empty.

When the engine is started, the evaporative emission canister is gradually purged as air is sucked into it through the shut-off valve. The hydrocarbon/air mixture passes through the EVAP canister purge valve and into the engine where it is burnt.

The diagnosis in ORVR cars is divided into two variants, normal and special, depending on the engine coolant temperature and the temperature of the intake air. This is to eliminate any affects of the fuel vapor evaporating.

An evaporative emission canister fitted by the tank is used on ORVR cars to store approx. 130 g hydrocarbons. The canister is filled with approx. 70-90 g hydrocarbons during normal refuelling. This is subsequently purged while the car is being driven so that it is normally empty the next time the car is refuelled.

From M01, there are three variants of emission requirements:

1. OBD II LEV for US/CA. Has full ORVR with tank integrity diagnosis and fuel vapor recovery as well as CHECK ENGINE lamp for emission-related faults.
2. E-OBD, EC2000 for EU/NO/CH. Has ORVR with vapor recovery but not tank integrity diagnosis, which means that cars with this variant of ORVR are not fitted with a shut-off valve or tank pressure sensor. The CHECK ENGINE lamp is on only in a few cases.
3. L-OBD for other markets. L-OBD is identical to E-OBD with the exception that in L-OBD, the CHECK ENGINE lamp does not come on for emission-related faults.

The EVAP canister is situated on top of the tank in cars with full ORVR or ORVR without tank integrity diagnosis. On cars without vapor recovery, it is situated under the front right wing.