Circuit Description
WARNING: This page is about a different car, the 2003 Buick Regal and 2003 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
The 1-2 shift solenoid valve is supplied with fused ignition voltage. The ground path is controlled by the PCM. When the PCM commands the solenoid OFF, a ground path is not provided and the filtered line pressure that is fed to the solenoid is exhausted. When the PCM commands the solenoid ON, a ground path is provided and the exhaust port is blocked, stopping the exhaust of line pressure.
The PCM identifies a 1-2 shift solenoid valve condition by monitoring the commanded gear versus gear ratio.
If the PCM detects a 2nd gear ratio when 1st gear is commanded and a 3rd gear ratio when 4th gear is commanded, then DTC P0751 sets. DTC P0751 is a type "B" DTC.