Circuit Description
The 3-2 shift solenoid (SS) valve assembly 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 circuit 1020. The vehicle control module (VCM) controls the solenoid by providing a ground path on circuit 687. During a 3-2 downshift, the 2-4 band applies as the 3-4 clutch releases. The VCM 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 VCM detects a continuous open, short to ground or short to power in the 3-2 SS valve assembly circuit, then DTC P0785 sets. DTC P0785 is a type A DTC.
Conditions for Running the DTC
| • | The system voltage is 10-19 volts. |
| • | The engine speed is greater than 450 RPM for 5 seconds. |
| • | The engine is not in fuel cutoff. |
Conditions for Setting the DTC
DTC P0785 sets if one of the following conditions occurs for 5 seconds:
Condition 1
The VCM commands the solenoid ON and the voltage feedback remains high (B+).
Condition 2
The VCM commands the solenoid OFF and the voltage feedback remains low (0 volts).
Action Taken When the DTC Sets
| • | The VCM illuminates the malfunction indicator lamp (MIL). |
| • | The VCM commands a soft landing to third gear. |
| • | The VCM commands maximum line pressure. |
| • | The VCM inhibits TCC engagement. |
| • | The VCM inhibits 4th gear if the transmission is in hot mode. |
| • | The VCM freezes shift adapts from being updated. |
| • | The VCM records the operating conditions when the Conditions for Setting the DTC are met. The VCM stores this information as Freeze Frame and Failure Records. |
| • | The VCM stores DTC P0785 in VCM history. |
Conditions for Clearing the MIL/DTC
| • | The VCM 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 VCM clears the DTC from VCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring. |
| • | The VCM 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 VCM. |
Diagnostic Aids
| • | Inspect the connectors at the VCM, the 3-2 SS valve and all other circuit connecting points for an intermittent condition. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. |
| • | Inspect the circuit wiring for an intermittent condition. Refer to Testing for Electrical Intermittents in Wiring Systems. |
Test Description
The item numbers below refer to the step numbers on the diagnostic table.
-
This step tests the ability of the VCM to control the solenoid.
-
This step tests for voltage to the solenoid.
-
This step tests the ability of the VCM and the wiring to control the ground circuit.
-
This step measures the resistance of the automatic transmission (AT) wiring harness assembly and the 3-2 SS valve assembly.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain Diagnostic System Check? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check (4.3L) or Powertrain On Board Diagnostic (OBD) System Check (5.0/5.7L) in Engine Controls | |||||||||
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 VCM. Are any of the following DTCs also set?
| -- | ||||||||||
3 | Inspect the TRANS fuse for an open. Refer to General Electrical Diagnosis in Wiring Systems. Is the fuse open? | -- | ||||||||||
Use the Scan Tool in order to command the 3-2 SS valve assembly ON and OFF three times, while listening to the bottom of the transmission pan (a stethoscope may be necessary). Does the solenoid click when commanded? | -- | Go to Diagnostic Aids | ||||||||||
Refer to Automatic Transmission Inline Harness Connector End View . Does the test lamp illuminate? | -- | |||||||||||
Refer to Automatic Transmission Inline Harness Connector End View . Does the test lamp turn ON and OFF with each command? | -- | |||||||||||
7 | Is the test lamp always ON? | -- | ||||||||||
Refer to Automatic Transmission Inline Harness Connector End View . Does the resistance measure within the specified range? | 20-32 ohms | |||||||||||
9 |
Do both readings measure greater than the specified value? | 250 K ohms | Go to Diagnostic Aids | |||||||||
10 |
Does the resistance measure within the specified range? | 20-32 ohms | ||||||||||
11 |
Do both readings measure greater than the specified value? | 250 K ohms | ||||||||||
12 |
Important: The condition that affects this circuit may exist in other connecting branches of the circuit. Refer to Power Distribution Schematics in Wiring Systems for complete circuit distribution. Test the power feed circuit (CKT 1020) of the 3-2 SS valve assembly for a short to ground between the IP fuse block and the AT inline 20-way connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||||||
13 |
Important: The condition that affects this circuit may exist in other connecting branches of the circuit. Refer to Power Distribution Schematics in Wiring Systems for complete circuit distribution. Test the power feed circuit (CKT 839) of the 3-2 SS valve assembly for a short to ground between the AT inline 20-way connector and the 3-2 SS valve assembly. Refer to Circuit Testing in Wiring Systems. Did you find a short to ground condition? | -- | ||||||||||
14 |
Did you complete the replacement? | -- | -- | |||||||||
15 |
Important: The condition that affects this circuit may exist in other connecting branches of the circuit. Refer to Power Distribution Schematics in Wiring Systems for complete circuit distribution. Test the power feed circuit (CKT 1020) of the 3-2 SS valve assembly for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | -- | |||||||||
16 | Test the control circuit (CKT 687) of the 3-2 SS valve assembly for a short to ground between the VCM connector C1 and the AT inline 20-way connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||||||
17 | Test the control circuit (CKT 687) of the 3-2 SS valve assembly for an open or short to power between the VCM connector C1 and the AT inline 20-way connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||||||
18 | Replace the AT wiring harness assembly. Refer to Valve Body . Did you complete the replacement? | -- | -- | |||||||||
19 | Replace the 3-2 SS valve assembly. Refer to Valve Body . Did you complete the replacement? | -- | -- | |||||||||
20 | Replace the VCM. Refer to VCM Replacement/Programming (4.3L) or VCM Replacement/Programming (5.0/5.7L) in Engine Controls. Did you complete the replacement? | -- | -- | |||||||||
21 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | System OK |
