Diagnostic Aids

WARNING: This page is about a different car, the 2010 Pontiac G5 and 2010 Chevrolet Cobalt. However, it is still accessible from the selected car via links, so may be relevant.

Road test the vehicle while monitoring the Transmission ISS parameter on the scan tool. The Transmission ISS parameter should vary with engine speed changes and not abruptly drop out.
Inspect for an open or shorted AT ISS wire.
Inspect for a disconnected AT ISS connector.
Inspect for a faulty AT ISS.