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Old 09-29-2019, 02:23 PM   #9
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Join Date: Jan 2011
Posts: 295

2001 SL1
Default Re: Secondary air injection system

2001 SL-1, the air pump is no longer powering up. Do they go bad? Brushes? Can they be repaired? What should I check first, the Air Pump power relay???

Originally Posted by fdryer View Post
Back pressure refers to positive pressure. Vacuum is vacuum. Either a vacuum exists (supplied from the intake manifold only when the engine's running) or not. Blower pressure, when the blower is running, supplies air to the exhaust system when the combination valve opens, feeding air (from the electric air pump) into the exhaust manifold to help heat up the catalytic converter.

Maybe some info can help from the service manual.

The AIR system is used to reduce hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOX) exhaust emissions by heating up the catalytic converters quicker on cold engine start-up. The conversion of exhaust emissions to carbon dioxide (CO2) and water can occur sooner as the catalytic converter reach the normal operating temperature around 527C (981F). The AIR system consists of:

*Air pump (1)
*Check valve (2)
*Air pump solenoid (3)
*Combination valve (4)
*Air pipe and hose (5)
*Vacuum hose (6)
*Air pump relay - located in underhood fuse block (UHFB). (7)
*Powertrain control module (PCM) - located underhood between the battery and power brake booster. (8)

The air pump is a permanently lubricated turbine type pump which requires no periodic maintenance. The PCM runs the air pump for a certain length of time when the engine is started within a certain ECT range. When the air pump is commanded ON, the PCM will command an internal driver ON which pulls the air pump relay circuit to ground allowing current to flow to the air pump.

The air pump solenoid is used to control vacuum to the combination valve. When the air pump relay is commanded ON, air pump running), the PCM will wait a short amount of time to command the air pump solenoid ON. The PCM turns the solenoid ON by controlling an internal driver that pulls the solenoid circuit to ground. The PCM waits to turn the solenoid ON in order for the air pump to pressurize which keeps exhaust gas from entering the air pump.

When the air pump and air pump solenoid are turned ON, vacuum to the combination valve will allow the spring loaded diaphragm, upper valve in the combination valve, to be pulled up. This will allow pressurized air from the air pump to flow around the reed valve, lower valve in combination valve, to the exhaust manifold.

Before the PCM commands the air pump relay OFF, it will first command the air pump solenoid OFF and wait a short amount of time before it commands the relay OFF. This keeps exhaust gas from entering the air pump.


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