For 1990-2009 cars
Master Electrical Component List
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice
Control Module References

### 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 475 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.

1. This step tests the ability of the PCM to control the solenoid.

2. This step tests for voltage to the solenoid.

3. This step tests the ability of the PCM and the wiring to control the ground circuit.

4. This step measures the resistance of the automatic transmission wiring harness assembly and the 3-2 SS valve.

#### DTC P0788

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.

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).

3. Record the DTC Freeze Frame and Failure Records.
4. Clear the DTC.

Are any of the following DTCs also set?

• | P2769

• | P2770

• | P0973

• | P0974

• | P0976

• | P0977

• | P2763

• | P2764

--

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
4 | Use the scan tool in order to command the 3-2 shift solenoid (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
5 |

1. Turn OFF the ignition.
2. Disconnect the AT inline 20-way connector, additional DTCs may set.
3. Install the J 44152 Jumper Harness (20 pins) on the engine side of the AT inline 20-way connector.
4. Turn ON the ignition, with the engine OFF.
5. Using the J 35616 GM Terminal Test Kit, connect a test lamp from the 3-2 SS valve ignition voltage circuit of the J 44152 to ground.

Refer to Automatic Transmission Inline 20-Way Connector End View.

Does the test lamp illuminate?

--

Go to Step 6

Go to Step 15

6 |

1. Connect a test lamp between the 3-2 SS valve ignition voltage and control circuits of the J 44152 . Refer to Testing for Continuity.
2. Use the scan tool in order to command the 3-2 SS valve assembly ON and OFF three times.

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
8 |

1. Install the J 44152 on the transmission side of the AT inline 20-way connector.
2. Using the DMM and the J 35616 , measure the resistance between the 3-2 SS valve ignition voltage and control circuits of the J 44152 . 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 Ω

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 Ω | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 11
10 |

1. Disconnect the AT wiring harness from the 3-2 SS valve.
2. Measure the resistance of the 3-2 SS valve.

Does the resistance measure within the specified range?

20-32 Ω

Go to Step 18

Go to Step 19

11 |

1. Disconnect the AT wiring harness from the 3-2 SS valve.
2. Measure the resistance from the component's terminals to ground.

Do both readings measure greater than the specified value?

250 K Ω

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 |

1. Test each solenoid for a short to ground.
2. Replace the faulty solenoid as necessary.

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:

1. Select DTC.
2. Select Clear Info.
3. Drive the vehicle in D3 or D4 and perform a 3-2 downshift. Ensure that the following conditions are met:

• | The PCM commands the 3-2 SS valve ON, and the voltage feedback drops to zero.

• | The PCM commands the 3-2 SS valve OFF, and the voltage feedback increases to B+.

• | All conditions are met for 5 seconds.

4. Select Specific DTC.
5. Enter DTC P0788.

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? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | System OK