DTC P0787 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 open or short to ground in the 4-3 downshift solenoid valve circuit, then DTC P0787 sets. DTC P0787 is a type C DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0787 Downshift Timing Solenoid Control Circuit Low Voltage
Conditions for Running the DTC
The engine is running for 5 seconds.
Conditions for Setting the DTC
The 4-3 downshift solenoid valve feedback circuit indicates a continuous open or short to ground for 4.4 seconds.
Action Taken When the DTC Sets
| • | The TCM does not illuminate the malfunction indicator lamp (MIL). |
| • | The TCM commands maximum line pressure. |
| • | 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 P0787 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 a non-emission related diagnostic fault occurring. |
| • | The TCM cancels the DTC default actions when the fault no longer exists and the DTC passes. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests the electrical operation of the solenoid.
-
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. Is DTC P0973, P0976, or P2764 also set? | -- | Go to Step 3 | Go to Step 8 | ||||
3 |
Did you find the condition? | -- | Go to Step 4 | Go to Step 6 | ||||
4 |
Important: The condition that affects this circuit may exist in other connecting branches of the circuit. Refer to Power Distribution Schematics for complete circuit distribution. Test the ignition 1 voltage circuit of the 4-3 downshift solenoid valve for a short to ground between the underhood fuse block and the AT inline 20-way connector. Refer to Testing for Short to Ground and Wiring Repairs. Did you find and correct the condition? | -- | Go to Step 23 | Go to Step 5 | ||||
5 |
Important: The condition that affects this circuit may exist in other connecting branches of the circuit. Refer to Power Distribution Schematics for complete circuit distribution. Test the ignition 1 voltage circuit of the 4-3 downshift solenoid valve for a short to ground between the AT inline 20-way connector and the 4-3 downshift solenoid valve. Refer to Testing for Short to Ground. Did you find the condition? | -- | Go to Step 20 | -- | ||||
6 | Test the ignition 1 voltage circuit of the 4-3 downshift solenoid valve for an open between the underhood fuse block and the AT inline 20-way connector. Refer to Testing for Continuity and Wiring Repairs. Did you find and correct the condition? | -- | Go to Step 23 | Go to Step 7 | ||||
7 | Test the ignition 1 voltage circuit of the 4-3 downshift solenoid valve for an open between the AT inline 20-way connector and the 4-3 downshift solenoid valve. Refer to Testing for Continuity. Did you find the condition? | -- | Go to Step 20 | -- | ||||
Does the solenoid click when commanded ON and OFF? | -- | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 9 | |||||
Is the test lamp ON when you command the solenoid ON, and OFF when you command the solenoid OFF? | -- | Go to Step 14 | Go to Step 10 | |||||
10 | Is the test lamp always ON? | -- | Go to Step 11 | Go to Step 13 | ||||
11 |
Is the test lamp ON? | -- | Go to Step 12 | Go to Step 22 | ||||
12 | Test the control circuit of the 4-3 downshift solenoid valve for a short to ground between the TCM connector and the AT inline 20-way connector. Refer to Testing for Continuity and Wiring Repairs. Refer to Testing for Short to Ground and Wiring Repairs. Did you find and correct the condition? | -- | Go to Step 23 | -- | ||||
13 | Test the control circuit of the 4-3 downshift solenoid valve for an open between the TCM connector and the AT inline 20-way connector. Did you find and correct the condition? | -- | Go to Step 23 | Go to Step 22 | ||||
Refer to Automatic Transmission Inline 20-Way Connector End View. Is the resistance within the specified range? | 19-31 Ω | Go to Step 17 | Go to Step 15 | |||||
15 | Is the resistance greater than the specified value? | 31 Ω | Go to Step 16 | Go to Step 17 | ||||
16 |
Refer to Testing for Continuity. Did you find a condition? | -- | Go to Step 20 | Go to Step 21 | ||||
17 | Measure the resistance from the 4-3 downshift solenoid valve control circuit of the J 44152 to ground. Refer to Automatic Transmission Inline 20-Way Connector End View. Is the resistance less than the specified value? | 100 Ω | Go to Step 18 | Go to Step 19 | ||||
18 | Test the control circuit of the 4-3 downshift solenoid valve for a short to ground between the AT inline 20-way connector and the 4-3 downshift solenoid valve. Refer to Testing for Short to Ground. Did you find the condition? | -- | Go to Step 20 | -- | ||||
19 | Measure the resistance between the 4-3 downshift solenoid valve control circuit and all other terminals of the J 44152 . Refer to Automatic Transmission Inline 20-Way Connector End View. Is the resistance less than the specified value? | 100 Ω | Go to Step 20 | Go to Step 21 | ||||
20 | Replace the automatic transmission wiring harness. Refer to Wiring Harness Replacement. Did you complete the replacement? | -- | Go to Step 23 | -- | ||||
21 | 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 23 | -- | ||||
22 | Replace the TCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 23 | -- | ||||
23 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | Go to Step 24 | Go to Step 2 | ||||
24 | 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 |
