DTC P0788 5.3L and 6.0L
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 voltage through the ignition voltage 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 throttle position.
When the TCM detects a continuous short to voltage in the 3-2 shift solenoid valve control circuit, then DTC P0788 sets. DTC P0788 is a type A DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0788 3-2 Shift Solenoid (SS) Control Circuit High Voltage
Conditions for Running the DTC
| • | The system voltage is 8-18 volts. |
| • | The engine speed is 475 RPM for 5 seconds. |
| • | Vehicle speed. |
Conditions for Setting the DTC
DTC P0788 sets if the TCM commands the solenoid ON and the voltage feedback remains high, B+.
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 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 P0788 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. |
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). Does the 3-2 Sol. CKT status parameter display OK? | -- | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 3 | ||||||
3 |
Refer to Automatic Transmission Inline 20-Way Connector End View . Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 4 | ||||||
4 |
Refer to Automatic Transmission Inline 20-Way Connector End View . Does the resistance measure less than the specified value? | 20 ohms | Go to Step 5 | Go to Step 7 | ||||||
5 |
Does the resistance measure less than the specified value? | 20 ohms | Go to Step 8 | Go to Step 7 | ||||||
6 | Test the control circuit of the 3-2 SS valve for a short to voltage between the TCM and the AT inline 20-way connector. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 10 | Go to Step 9 | ||||||
7 | Replace the AT internal wiring harness. Did you complete the replacement? | -- | Go to Step 10 | -- | ||||||
8 | Replace the 3-2 SS valve. Refer to Control and Shift Solenoids Replacement . 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 |
DTC P0788 4.2L
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 voltage circuit. The powertrain control module (PCM) 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 PCM 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 PCM detects a continuous short to voltage in the 3-2 SS valve circuit, then DTC P0788 sets. DTC P0788 is a type A DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0788 3-2 Shift Solenoid (SS) Control Circuit High Voltage
Conditions for Running the DTC
| • | The engine speed is greater than 450 RPM for 5 seconds. |
| • | The engine is not in fuel cutoff. |
Conditions for Setting the DTC
DTC P0788 sets if the following condition occurs for 5 seconds:
The PCM commands the solenoid ON and the voltage feedback remains high, B+.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL). |
| • | The PCM commands a soft landing to third gear. |
| • | The PCM commands maximum line pressure. |
| • | The PCM inhibits torque converter clutch (TCC) engagement. |
| • | The PCM inhibits fourth gear in Hot Mode. |
| • | The PCM freezes transmission adaptive functions from being updated. |
| • | The PCM inhibits 3-2 downshifts above 48 km/h (30 mph). |
| • | The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records. |
| • | The PCM stores DTC P0788 in PCM history. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes. |
| • | A scan tool can clear the MIL/DTC. |
| • | The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring. |
| • | The PCM cancels the DTC default actions when the fault no longer exists and/or the ignition switch is OFF long enough in order to power down the PCM. |
Test Description
The item numbers below refer to the step numbers on the diagnostic table.
-
This step tests the ability of the PCM to control the solenoid.
-
This step tests for voltage to the solenoid.
-
This step tests the ability of the PCM and the wiring to control the ground circuit.
-
This step measures the resistance of the automatic transmission wiring harness assembly 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 powertrain control module (PCM). Are any of the following DTCs also set?
| -- | Go to Step 3 | Go to Step 4 | ||||||||||||||||
3 | Inspect the TRANS fuse for an open. Refer to Circuit Protection - Fuses . Is the fuse open? | -- | Go to Step 12 | Go to Step 5 | ||||||||||||||||
Use the scan tool in order to command the 3-2 SS valve ON and OFF 3 times, while listening to the bottom of the transmission pan, a stethoscope may be necessary. Does the solenoid click when commanded? | -- | 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 . 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 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 control circuit 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 |
Does the resistance measure within the specified range? | 20-32 ohms | Go to Step 18 | Go to Step 19 | ||||||||||||||||
11 |
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 voltage circuit of the 3-2 SS valve for a short to ground between the 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 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. Refer to Testing for Short to Ground . Did you find a short to ground condition? | -- | Go to Step 18 | Go to Step 14 | ||||||||||||||||
14 |
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 voltage 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 PCM 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 a short to voltage between the PCM and the AT inline 20-way connector. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 20 | ||||||||||||||||
18 | Replace the AT wiring harness. Refer to Valve Body and Pressure Switch Replacement . Did you complete the replacement? | -- | Go to Step 21 | -- | ||||||||||||||||
19 | Replace the 3-2 SS valve. Refer to Valve Body and Pressure Switch Replacement . Did you complete the replacement? | -- | Go to Step 21 | -- | ||||||||||||||||
20 | Replace the PCM. Refer to Control Module References . 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 |
