Symptoms

- Engine Light ON (or Service Engine Soon Warning Light) - Engine hesitation

Possible Causes

- Vacuum hoses damaged. - Air Pump inoperative. - Air bypass solenoid circuit open. - Air bypass solenoid leaking/blocked or stuck open/closed. - Air diverter valve leaking/blocked or stuck open/closed. - Air air hoses r

When Detected

The secondary air injection system does not detect the presence of air in the exhaust when introduced by the secondary air injection system.

Tech Notes

Service Bulletin 1999-2003 Chevrolet Blazer, S10 1999-2001 GMC Jimmy 1999-2003 GMC Sonoma 1999-2001 Oldsmobile Bravada

Description

An air pump is used on the vehicle to lower tail pipe emissions on start-up. The Powertrain Control Module PCM grounds the Air pump relay control circuit which energizes the Air pump. The PCM also grounds the Air combination valve vacuum control solenoid circuit, which energizes the Air vacuum control solenoid. Vacuum is then applied to both Air combination valve diaphragms which opens the shut off valves. The PCM enables both circuits simultaneously when Air system operations id desired. When the AIR system is active, then Air pump forces fresh air into the exhaust stream in order to accelerate catalyst operation. The AIR combination valves replace the conventional check valves. When the AIR system is inactive the shut off valves prevent air flow in either direction.