Diagnostic Aids

The throttle valve is spring loaded to a slightly open position. The throttle valve should be open about 20 percent. This is referred to as the rest position. The throttle valve should not be completely closed nor should they be open any more than the specified amount. The throttle valve should move open and to the closed position without binding under the normal spring pressure. The throttle should NOT be free to move open or closed WITHOUT spring pressure. Replace throttle body if any of these conditions are found. See REMOVAL & INSTALLATION - BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.

The scan tool has the ability to operate the throttle control system using Special Functions. Actuate the throttle valve using the throttle blade control function located in the TAC System menu. This function will operate the throttle valve through the entire range in order to determine if the throttle body and system operate correctly. Check for the following conditions:

• Use the Connector Test Adapter Kit (J-35616-A) for any test that requires probing the PCM harness connector or a component harness connector.
• Poor connections at the PCM or at the component. Inspect the harness connectors for a poor terminal to wire connection.
• If the condition is intermittent, see INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.