Secondary Air Injection. Overview - BMW 5251 Service Manual

130-75
Fuel
Injection
Secondary air injection, overview
The secondary air system pumps ambient air into the exhaust
stream afteracoid engine start to reduce the warm-up time of
the catalytic converters and to reduces HC and CO emis-
sions. The ME 7.2 ECM controls and monitors the secondary
air injection system. The secondary air pump operates at a
starttemperature of between 10°C (50°F) and 40°C (104°F).
and continues to operate for a maximum of 2 minutes at idle
speed.
The electric air pump draws in ambient air and supplies it to
the checlc valve. The vacuum vent valve (solenoid) switches
vacuum to open the checlc valve when activated by the ECM.
Once opened, the checlc valve allows air to be pumped into
the exhaust stream.
4
The secondary air injection system consists of the following
components:
1. Secondary air pump relay
2. Oxygen sensors
3. Catalytic converters
4. Electric air pump
5. Non-return valve
6. Vacuum vent valve