Secondary Throttle Valve: Testing and Inspection

Chart C-2D:

Chart C-2D Wiring Diagram:

CIRCUIT DESCRIPTION: The secondary port throttle valve system is used to allow the intake of air and fuel through the secondary intake valves under high engine speed and load conditions. The vacuum sensor is used to detect improper operation of the system when the ECM commands the secondary port throttle valves open or closed with the secondary port throttle valve solenoid. The electric vacuum pump is turned ON whenever vacuum in the vacuum reservoir tank drops below 41 kPa (12" Hg) and is turned OFF when vacuum is above 57 kPa (17" Hg).

NOTE: For referrals to charts not included in DIAGNOSTIC CHARTS, see COMPUTERIZED ENGINE CONTROLS.


TEST DESCRIPTION: The numbers below refer to the circled numbers on the diagnostic chart.

1. When selecting "Field Service Mode" with the "Scan" tool, it energizes the secondary port throttle valve solenoid and allows vacuum to the vacuum sensor. Turning the ignition ON will energize the electric vacuum pump and should maintain 57 kPa (17" Hg) in the vacuum reservoir tank.
2. The electric vacuum pump should operate with the key ON because the vacuum to the pump is less than 41 kPa (12" Hg).
3. The electric vacuum pump should operate with the key ON because the vacuum to the pump is less than 41 kPa (12" Hg). When the electric vacuum pump hose fitting is plugged the pumps internal pressure should shut the pump OFF.

DIAGNOSTIC AIDS:

If the secondary port throttle valve system has a vacuum leak, check for disconnected vacuum hoses, leaking check valves or fittings. Check the vacuum hoses under the plenum for cracks, splits and proper routing.