DTC P0787 or P0788 Hybrid

Diagnostic Instructions

DTC Descriptors

DTC P0787:  Downshift Timing Solenoid Control Circuit Low Voltage

DTC P0788:  Downshift Timing Solenoid Control Circuit High Voltage

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
Ignition Circuit	P2534	P2534	--	--
Solenoid Control Circuit	P0787	P0787	P0788	--

Typical Scan Tool Data

4-3 Downshift Sol. Parameter Data

Circuit	Short to Ground	Open	Short to Voltage
Operating Conditions: Engine running Parameter Normal Range: OK
4-3 Downshift Sol.	ON	ON	ON
4-3 Sol. CKT Status	Open/Short to GND	Open/Short to GND	Short to Volts

Circuit/System 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 4-3 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.

Conditions for Running the DTC

P0787

The engine is running for 5 seconds.

P0788

The engine is running for 2 seconds.

Conditions for Setting the DTC

P0787

The 4-3 downshift solenoid valve feedback circuit indicates a continuous open or short to ground for 4.4 seconds.

P0788

The 4-3 downshift solenoid valve feedback circuit indicates a continuous short to voltage for 150 milliseconds.

Action Taken When the DTC Sets

Conditions for Clearing the DTC

DTC P0787 and P0788 are Type C DTCs.

Reference Information

Schematic Reference

Automatic Transmission Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Special Tools

J 44152 Jumper Harness (20 pins)

Circuit/System Verification

1. Verify that DTC P0961, P0973, P0974, P0976, or P2764 are not set.

⇒	If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.

2. Ignition ON, engine OFF, observe the 4-3 Sol. CKT Status parameter while commanding the 4-3 downshift solenoid ON and OFF with a scan tool. The reading should display OK or Indeterminate.
3. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

Important: Additional DTCs may set when disconnecting the automatic transmission inline 20-way connector.

1. Ignition OFF, disconnect the automatic transmission (AT) inline 20-way connector at the transmission.
2. Install J 44152 on the engine side of the AT inline 20-way connector.
3. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal E and ground.

⇒	If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test all components connected to the ignition circuit and replace as necessary.

4. Connect a test lamp between the control circuit terminal F and the ignition circuit terminal E.
5. Command the 4-3 downshift solenoid ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the TCM.

⇒	If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the TCM.

6. If all circuits test normal, test the internal transmission harness and the 4-3 downshift solenoid.

Component Testing

1. Ignition OFF, disconnect the automatic transmission (AT) inline 20-way connector at the transmission.
2. Install J 44152 on the transmission side of the AT inline 20-way connector.
3. Test for 15-25 ohms of resistance between the control terminal F and the ignition terminal E of the transmission.

⇒	If not within the specified range, test the circuits for a short to ground or an open/high resistance. If a circuit is shorted or open replace the internal transmission harness, if the circuits test normal, replace the 4-3 downshift solenoid.

4. Test for infinite resistance between each terminal and the transmission housing/case.

⇒	If not the specified value, test the circuits for a short to ground or an open/high resistance. If a circuit is shorted replace the internal transmission harness, if the circuits test normal, replace the 4-3 downshift solenoid.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.