Secondary Air Injection System Description
The secondary air injection (AIR) system helps reduce exhaust emissions.
The system forces fresh filtered air into the exhaust stream in order to accelerate
catalyst operation.
The system includes the following:
| • | AIR pump--The AIR pump supplies filtered air through the
AIR system into the exhaust stream. The control module provides ground
for the pump relay. Battery voltage is then applied to the pump. The filter
is the only serviceable part of the pump. |
| • | AIR vacuum control solenoid--The AIR vacuum control solenoid
controls the AIR shut-off valves. When the AIR system is enabled, the
control module provides a ground to the solenoid. Enabling the solenoid
allows engine vacuum to be applied to the AIR shut-off valves. |
| • | AIR shut-off valves--The AIR shut-off valves are vacuum operated.
When the AIR system is enabled, vacuum is applied to the valves. The vacuum
opens the valves and allows air from the AIR pump to flow to the check
valves. |
| • | Check valve--The check valve prevents back flow of exhaust
gases into the AIR injection system. An AIR pump that had become inoperative
and had shown indications of having exhaust gases in the outlet port would
indicate check valve failure. |
| • | Plumbing--The plumbing carries the air from the pump to the
exhaust stream. This includes the hoses, pipes, and clamps. The plumbing can
be tested for leaks using a soapy water solution. With the AIR pump running,
bubbles will form if a leak exists. |
Results of Incorrect Operation
If no air or, oxygen, flow enters the exhaust stream, the start up emission
levels will rise. The control module can detect a system flow problem using
the pre-catalyst heated oxygen sensor (HO2S) and short term FT. If a system
flow problem is present the HO2S voltage will not indicate an expected
lean condition, short term FT will not increase, and a diagnostic trouble
code (DTC) will set.
If incorrect voltage is present on the vacuum control solenoid or the
pump relay control circuits, the device will not operate. This will be detected
by the control module and a DTC will set.
The following DTCs can set if a secondary air injection
fault is detected:
| • | DTC P0410--A system flow problem has been detected. |
| • | DTC P0412--A vacuum control solenoid control circuit
problem has been detected. |
| • | DTC P0418--A pump relay control circuit problem has
been detected. |
