P0787
DTC P0787
Circuit Description
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.
When the TCM detects a continuous open, short to ground or short to voltage in the 3-2 SS valve circuit, then DTC P0787 sets. DTC P0787 is a type A DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0787 3-2 Shift Solenoid (SS) Control Circuit Low Voltage
Conditions for Running the DTC
^ The system voltage is 10 - 18 volts.
^ The engine speed is greater than 450 RPM for 5 seconds.
^ Vehicle speed is less than 200 km/h (124 mph).
Conditions for Setting the DTC
DTC P0787 sets if one of the following conditions occurs for 5 seconds:
Condition 1
The TCM commands the solenoid ON and the voltage feedback remains high, B+.
Condition 2
The TCM commands the solenoid OFF and the voltage feedback remains low, 0 volts.
Action Taken When the DTC Sets
^ The TCM requests the engine control module (ECM) to illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
^ The TCM commands maximum line pressure.
^ The TCM freezes transmission adaptive functions.
^ The TCM commands 3rd gear.
^ The TCM inhibits TCC engagement.
^ At the time of the first failure, the TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information as a Failure Record.
^ At the time of the second failure, the ECM records the operating conditions when the Conditions for Setting the DTC are met. The ECM stores this information as a Freeze Frame.
^ The TCM stores DTC P0787 in TCM history during the second consecutive trip in which the Conditions for Setting the DTC are met.
Conditions for Clearing the DTC
^ The ECM turns OFF the MIL after the 4th consecutive drive trip in which the TCM does not send a MIL illumination request.
^ A scan tool can clear the DTC.
^ The TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without a non-emission related diagnostic fault occurring.
^ The TCM cancels the DTC default actions when the ignition is OFF long enough in order to power down the TCM.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
4. This step tests the ability of the TCM to control the solenoid.
5. This step tests for voltage to the 3-2 SS valve.
6. This step tests the ability of the TCM and wiring to control the ground circuit.
8. This step measures resistance of the automatic transmission (A/T) wiring harness and the 3-2 SS valve.
