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 or short to ground 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 8-18 volts. |
| • | The engine speed is greater than 475 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 transmission control module (TCM) requests the engine control module (ECM) to illuminate the malfunction indicator lamp (MIL). |
| • | The TCM commands third gear. |
| • | The TCM commands maximum line pressure. |
| • | The TCM inhibits torque converter clutch (TCC) engagement. |
| • | The TCM freezes transmission adaptive functions. |
| • | 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 third 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 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.
-
This step tests the ability of the TCM to control the solenoid.
-
This step tests for voltage to the 3-2 SS valve.
-
This step tests the ability of the TCM and wiring to control the ground circuit.
-
This step measures resistance of the automatic transmission (AT) wiring harness and the 3-2 SS valve.
Step | Action | Values | 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 transmission control module (TCM). Are any of the following DTCs also set?
| -- | Go to Step 3 | Go to Step 4 | ||||||||||
3 | Inspect the ignition voltage supply fuse for an open. Refer to Circuit Protection - Fuses . Is the fuse open? | -- | Go to Step 12 | Go to Step 5 | ||||||||||
With a scan tool, command the 3-2 Downshift Solenoid ON. Does the 3-2 Sol. CKT status parameter display OK when commanded ON? | -- | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 5 | |||||||||||
Refer to Automatic Transmission Inline 20-Way Connector End View . Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 15 | |||||||||||
Refer to Automatic Transmission Inline 20-Way Connector End View and Testing for Continuity . Does the test lamp turn ON and OFF with each command? | -- | Go to Step 8 | Go to Step 7 | |||||||||||
7 | Is the test lamp always ON? | -- | Go to Step 16 | Go to Step 17 | ||||||||||
Refer to Testing for Continuity . Refer to Automatic Transmission Inline 20-Way Connector End View . Does the resistance measure within the specified range? | 20-32 ohms | Go to Step 9 | Go to Step 10 | |||||||||||
9 | Measure the resistance from the 3-2 SS valve ignition voltage and control circuits to ground. Refer to Testing for Continuity . Do both readings measure greater than the specified value? | 250 K ohms | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 11 | ||||||||||
10 |
Refer to Testing for Continuity . Does the resistance measure within the specified range? | 20-32 ohms | Go to Step 18 | Go to Step 19 | ||||||||||
11 |
Refer to Testing for Continuity . Do both readings measure greater than the specified value? | 250 K ohms | Go to Step 18 | Go to Step 19 | ||||||||||
12 |
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 circuit of the 3-2 SS valve for a short to ground between the fuse block-underhood 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 21 | Go to Step 13 | ||||||||||
13 |
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 voltage circuit of the 3-2 SS valve for a short to ground between the AT inline 20-way connector and the 3-2 SS valve assembly. Refer to Testing for Short to Ground . Did you find a short to ground condition? | -- | Go to Step 18 | Go to Step 14 | ||||||||||
14 |
Refer to Testing for Short to Ground . Did you complete the replacement? | -- | Go to Step 21 | -- | ||||||||||
15 |
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 circuit of the 3-2 SS valve for an open. Refer to Testing for Continuity and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 21 | -- | ||||||||||
16 | Test the control circuit of the 3-2 SS valve for a short to ground between the TCM 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 21 | Go to Step 20 | ||||||||||
17 | Test the control circuit of the 3-2 SS valve for an open between the TCM 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 21 | Go to Step 20 | ||||||||||
18 | Replace the AT wiring harness. Did you complete the replacement? | -- | Go to Step 21 | -- | ||||||||||
19 | Replace the 3-2 SS valve. Refer to Control and Shift Solenoids Replacement . Did you complete the replacement? | -- | Go to Step 21 | -- | ||||||||||
20 | Replace the TCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 21 | -- | ||||||||||
21 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | Go to Step 22 | Go to Step 2 | ||||||||||
22 | 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 |
