DTC P0788 Hybrid
Circuit Description
The 4-3 downshift solenoid valve controls transmission fluid pressure acting on the shift timing valve to position the valves for the appropriate gear. The 4-3 downshift solenoid valve is a normally closed exhaust valve located on the channel plate. Ignition voltage is supplied to the solenoid. The transmission control module (TCM) commands the solenoid ON or OFF by providing a ground path. When the 43 downshift solenoid valve is commanded ON, the TCM senses low voltage. When the 4-3 downshift solenoid valve is commanded OFF, the TCM senses high voltage.
If the TCM detects a continuous short to voltage in the 4-3 downshift solenoid valve circuit, then DTC P0788 sets. DTC P0788 is a type C DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0788 Downshift Timing Solenoid Control Circuit High Voltage
Conditions for Running the DTC
The engine is running for 2 seconds.
Conditions for Setting the DTC
The 4-3 downshift solenoid valve feedback circuit indicates a continuous short to voltage for 150 milliseconds.
Action Taken When the DTC Sets
| • | The TCM does not illuminate the malfunction indicator lamp (MIL). |
| • | The TCM freezes transmission adaptive functions. |
| • | The TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information as Failure Records. |
| • | The TCM stores DTC P0788 in TCM history. |
Conditions for Clearing the DTC
| • | A scan tool can clear the DTC. |
| • | The TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without an emission related diagnostic fault occurring. |
| • | The TCM cancels the DTC default actions when the ignition switch 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.
-
This step tests the TCM and the wiring to the transmission.
-
This step verifies that the circuit has the correct resistance.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
2 |
Important: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the TCM. Does the scan tool display indicate a short to voltage? | -- | Go to Step 3 | Go to Testing for Intermittent Conditions and Poor Connections |
Is the test lamp ON? | -- | Go to Step 4 | Go to Step 5 | |
4 | Test the control circuit of the 4-3 downshift solenoid valve for a short to voltage between the TCM connector and the AT inline 20-way connector. Refer to Testing for a Short to Voltage and Wiring Repairs. Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9 |
Is the resistance less than the specified value? | 19 Ω | Go to Step 6 | Go to Testing for Intermittent Conditions and Poor Connections | |
6 |
Is the resistance less than the specified value? | 19 Ω | Go to Step 7 | Go to Step 8 |
7 | Replace the automatic transmission wiring harness. Refer to Wiring Harness Replacement. Did you complete the replacement? | -- | Go to Step 10 | -- |
8 | Replace the 4-3 downshift solenoid valve. Refer to Control Valve Body Spacer Plate and 4-3 Downshift On/Off Solenoid Removal and Control Valve Body Spacer Plate and 4-3 Downshift On/Off Solenoid Installation. Did you complete the replacement? | -- | Go to Step 10 | -- |
9 | Replace the TCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 10 | -- |
10 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | Go to Step 11 | Go to Step 2 |
11 | With the scan tool, observe the stored information, capture info. and DTC info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK |
