Air Injection: Description and Operation

Secondary Air Injection Function

ENGINE 104.941,
104.943 /944 /991 /994 as of 1.8.96
ENGINE 104.995
with CODE (494a) USA version
with CODE (807) Model year 1997
with CODE (808) Model year 1998
with CODE (498) as of Model Year 97 Japanese version
ENGINE 111.973,
111.975 as of 1.8.96
ENGINE 111.974
with CODE (494a) USA version
with CODE (807) Model year 1997
with CODE (808) Model year 1998
ENGINE 119.980 /981 /982 /985
with CODE (491) U.S. version
with CODE (923a) low emission D3
as of 12/96




Shown on Engine 119
126 Aspirator shutoff valve
B11/4 Coolant temperature sensor
K17 AIR relay module
L5 Crankshaft position sensor
M16/1 Electronic accelerator (EA)/ cruise control (CC)/ idle speed control (ISC) actuator
M33 Electric air pump
N3/10 ME control module
Y32 air pump switchover valve

The secondary air injection heats up the catalytic converter more rapidly to its operating temperature and thus improves the emission levels in the warming-up phase.

Function
The electric air pump (M33) is actuated through the secondary air injection relay (K17) The current consumption of the electric air pump (M33) is as much as 35 A.

Air injection relay and air pump switchover valve (Y32) are actuated simultaneously by the motor electronics control module for maximum 90 seconds after engine start, if:
- Coolant temperature > 10 °C and < 60 °C
- Engine speed < 3000 rpm
- Throttle valve not fully opened

After an actuation, the air injection remains deactivated until the coolant temperature has risen to more than approx. + 60 °C and then drops again to below 40 °C.

The pump draws in air through a maintenance-free filter and pumps it to the air shutoff valve. The valve at the same time prevents exhaust gases from flowing back to the air pump (check valve discontinued).

The air pump switchover valve passes on the intake manifold pressure to the aspirator shutoff valve (126). This opens and the air delivered by the air pump is pressed into the exhaust manifold. The injected air reacts with the hot exhaust gases in the outlet port. An oxidation of carbon monoxides (CO) and hydrocarbon (HC) takes place and results in an additional increase in the exhaust temperature.

Engines with supercharger
The injected air is removed on the thrust side through the supercharger. An air pump is not required.