Secondary Air Injection. Overview - BMW 5251 Service Manual

Fuel Injection
1
NOTE-
The 1998 5281' with MS 41.1 requires a barometric pressure
sensor input signal for activation of the LDP check. This sen-
sor is located on the passenger side strut tower f o ~ l a r d of
ABS/ASC hydraulic unit.
Evaporative emissions
1. ECM
2. Purge valve
3.
Leak detection pump (LDP) (in
lefl rear wheel housing)
4. Filter
5.
Liquid vapor separator
6. Purge canister
7. Fuel tank
Secondary air injection, overview
The secondary air system pumps ambient air into the exhaust
stream afler a cold engine start to reduce the warm up time of
the catalytic converters and to reduces HC and CO emis-
sions. The ECM controls and monitors the secondary air in-
jection system. The secondary air pump operates at a start
temperature 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 divertervalve. The vacuum ventvalve (solenoid) switches
vacuum to open the divertervalve when activated by the
ECM. Once opened, the diverter valve allows air to be
pumped into the exhaust stream.