• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
• | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
• | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
---|---|---|---|---|
3-2 Solenoid Circuit Low Voltage | P0787 | P0787 | -- | -- |
3-2 Solenoid Circuit High Voltage | -- | -- | P0788 | -- |
The 3-2 shift solenoid (SS) valve is a normally-closed, 3-port, on/off device that controls the 3-2 downshift. The solenoid attaches to the control valve body within the transmission. The solenoid receives ignition voltage through the ignition 1 circuit. The transmission control module (TCM) controls the solenoid by providing a ground path on the 3-2 shift solenoid valve control circuit. During a 3-2 downshift, the 2-4 band applies as the 3-4 clutch releases. The TCM varies the timing between the 3-4 clutch release and the 2-4 band apply depending on the vehicle speed and the throttle position.
• | The system voltage is 8-18 volts. |
• | The engine speed is greater than 475 RPM for 5 seconds. |
• | Vehicle speed is less than 200 km/h (124 mph). |
• | The system voltage is 8-18 volts |
• | The engine speed is greater than 475 RPM for 5 seconds. |
• | Vehicle speed is less than 200 km/h (124 mph). |
The following condition occurs for 5 seconds:
The TCM commands the solenoid OFF and the voltage feedback remains low, 0 volts.
The TCM commands the solenoid ON and the voltage feedback remains high, B+.
• | DTC P0787 is a Type B DTC. |
• | The TCM inhibits 3-2 shift until vehicle speed is 20 km/h (12 mph) or less. |
• | The TCM freezes transmission adaptive functions. |
• | DTC P0788 is a Type B DTC. |
• | The TCM freezes transmission adaptive functions. |
DTC P0787 and P0788 are Type B DTCs.
Automatic Transmission Controls Schematics
Transmission General Information
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Transmission Control Module Scan Tool Information
• | J 35616 GM-Approved Terminal Test Kit |
• | J 44152 Jumper Harness (20 pins) |
Verify that DTCs P0961, P0973, P0976, P2764, P2769 have not set, if so, diagnose first. With a scan tool, command the 3-2 downshift solenoid ON and OFF.
⇒ | If the fuse is open, test the ignition 1 voltage circuit and the affected control circuit for a short to ground between the Fuse Block-Underhood and the AT inline 20-way connector. |
⇒ | If the test lamp is always OFF, test the circuit for an open. |
⇒ | If resistance is greater than the specified range, test the circuits for an open. If the resistance is less than the specified range, test for a faulty solenoid or a shorted together condition. |
⇒ | If the resistance is less than 250K ohms, test the ignition 1 voltage circuit for a short to ground. |
⇒ | If the resistance is greater than 250K ohms, test the affected control circuit for a short to ground. |
⇒ | If the resistance is not within the specified range, remove the affected solenoid. |
⇒ | If the resistance is not within the specified range, replace the affected solenoid. |
Perform the Diagnostic Repair Verification after completing the repair.
• | Refer to Control Module References for replacement, setup, and programming |