I was watching some C5 start up videos to hear mufflers on youtube, and hear the sound I've heard for years, subconsciously, just now noticed it!

It sounds like a electric motor, or something then goes away.

Is that the electric air injection pump pushing air into the tubes to heat up the cats?

 

Its the air pump. Only works on cold start. Works like a choke on a carburetor. It injects air into the exhaust system upstream from the oxygen sensors. So the sensors 'see" too much air and not enough fuel and richen the air/fuel ratio to correct. In other words the computer is tricking itself. Kinda funny. Stays on for a set number of seconds. I think around 90. By then motor is warm enough to take over on its own. And that's it!

 

I’m thinkin a little differently on the air pump operation. Yes it dumps air into the exhaust but this is to heat the O2’s faster, not to trick anything. The PCM ignores the signal from O2 sensors until the engine has warmed up.

 

You took the words right out of my mouth!!! Its only function is to allow primary CAT's to get up to operating temp earlier to meet emissions standards.

The AIR pump does run during normal driving. The PCM turns it on briefly to run a test to see if the AIR system is functioning correctly.

Secondary Air Injection (AIR) System Description
Secondary Air Injection System Description
The Air Secondary Injection (AIR) pump on this vehicle is designed to lower the exhaust emission levels after engine start up.

The Powertrain Control Module (PCM) commands the AIR pump relay ON, by supplying a ground to the relay control circuit. This action energizes the AIR pump which forces air (oxygen) into the exhaust stream. The PCM also commands the AIR vacuum solenoid valve ON, by supplying a ground to the control circuit of the AIR solenoid. With the AIR solenoid activated engine vacuum is then applied to the AIR shut-off valve. Freash air from the AIR pump then enters into the exhaust stream. The air that is introduced into the exhaust system accelerates catalysts operation reducing exhaust emission levels. When the AIR system is inactive, the AIR shut-off valve and check valves prevent airflow in either direction.

The system includes the following components:

The AIR pump relay-- The AIR pump relay supplies high current to the AIR pump voltage supply circuit. The PCM commands the AIR relay ON by suppling a ground on the control circuit of the relay. This action closes the internal contacts of the AIR relay, energizing the AIR pump.
The AIR pump--The AIR pump supplies fresh air through the secondary air injection system into the exhaust stream. The PCM supplies a ground for the AIR pump relay. Battery voltage is then applied to the AIR pump. The inlet filter is the only serviceable part of the pump.
The AIR vacuum control solenoid--The AIR vacuum control solenoid controls the AIR shut-off valve. When the AIR system is enabled, the PCM supplies a ground to the solenoid. This enables the solenoid, allowing engine vacuum to be applied to the AIR shut-off valve.
The AIR shut-off valve--The AIR shut-off valve is vacuum operated. When the AIR system is enabled, engine vacuum is applied to the valve. The vacuum opens the valve and allows air from the AIR pump to flow to the check valves. When inactive the shut -off valve prevents airflow in either direction.
The check valves--The check valves prevent back flow of exhaust gases into the AIR system. A shut-off valve that has become inoperative, shows indications of exhaust gases in the outlet port, or heat damaged hoses may indicate a check valve failure.
The Pipes/Hoses--The pipes/hoses carry the air from the AIR pump to the exhaust stream. The pipes/hoses 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
The PCM detects a system airflow problem by monitoring the heated oxygen senors (HO2S) and Short Term Fuel Trim (FT) values during normal open loop system operation. This is called a passive test. If the passive test indicates a pass, the PCM takes no further action. If the passive test fails or is inconclusive, the PCM diagnostic will proceed with an intrusive or active test. The PCM will command the AIR system ON, during normal closed loop operation and under normal operating conditions. This is called an active test. The active test will pass or fail based on the response from the HO2S. A lean HO2S response indicates that the AIR system is functioning normally. An increasing Short Term Fuel Trim value also indicates a normally functioning system. The AIR diagnostic consists of the combination of the passive and active test. It requires failure of the passive and active tests on two consecutive key cycles to illuminate the malfunction indicator lamp (MIL) and store a DTC. If the PCM detects that the HO2S and Short Term FT did not respond as expected on both of the engine banks DTC P0410 sets. If the PCM detects that the HO2S and Short Term FT did not respond as expected on only one of the engine banks DTC P1415 bank 1 or P1416 bank 2 sets.

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 DTC P0412 for the solenoid or P0418 for the relay sets.

The following DTCs can set if a secondary air injection fault is detected:

P0410-- A system flow problem has been detected.
P0412--A vacuum control solenoid control circuit problem has been detected.
P0418-- A pump relay control circuit problem has been detected.
P1415--A Bank 1 flow problem has been detected.
P1416--A Bank 2 flow problem has been detected.

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Document ID# 672617
2001 Chevrolet/Geo Corvette

 

I stand corrected. Thank you. Hey I'm still learning something new everyday!