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 or short to ground in the 3-2 SS valve assembly circuit or the 3-2 SS valve assembly, 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 either of the following conditions occurs for 5 seconds:
| • | The VCM commands the solenoid ON and the voltage input remains high (B+). |
| • | The VCM commands the solenoid OFF and the voltage input 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 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 clears the DTC from VCM history. |
| • | 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 the ignition switch is OFF long enough in order to power down the VCM. |
Diagnostic Aids
| • | Inspect the wiring at the VCM, the transmission connector and all other circuit connecting points for the following conditions: |
| - | A backed out terminal |
| - | A damaged terminal |
| - | Reduced terminal tension |
| - | A chafed wire |
| - | A broken wire inside the insulation |
| - | Moisture intrusion |
| - | Corrosion |
| • | When diagnosing for an intermittent short or open condition, massage the wiring harness while watching the test equipment for a change. |
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 (A/T) wiring harness assembly and the 3-2 SS valve assembly.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check (4.3L) or Powertrain On Board Diagnostic (OBD) System Check (5.0L and 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 |
Refer to Wiring Repairs in Wiring Systems. Did you find a short to ground condition? | -- | ||||||||||
Using the transmission output control function on the scan tool, 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? | -- | |||||||||||
6 |
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. Repair the open or short to ground in ignition feed circuit 1020 (PNK) to the 3-2 SS valve assembly. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | -- | |||||||||
Does the test lamp illuminate when you command the shift solenoid ON, and turn off when you command OFF? | -- | |||||||||||
8 |
Refer to General Electrical Diagnosis in Wiring Systems. Refer to Wiring Repairs in Wiring Systems. Did you find an open, short to ground or short to power condition? | -- | ||||||||||
9 | Replace the VCM. Refer to VCM Replacement/Programming (4.3L) or VCM Replacement/Programming (5.0L and 5.7L) in Engine Controls. Is the replacement complete? | -- | -- | |||||||||
Refer to Automatic Transmission Inline Harness Connector End View . Is the resistance within the specified range? | 20-32 ohms | |||||||||||
11 |
Is the resistance within the specified range? | 20-32 ohms | ||||||||||
12 |
Are both measurements greater than the specified value? | 250 K ohms | Go to Diagnostic Aids | |||||||||
13 |
Are both readings greater than the specified value? | 250 K ohms | ||||||||||
14 | Replace the A/T wiring harness assembly. Refer to TCC PWM Solenoid, TCC Solenoid, and Wiring Harness Replacement. Is the replacement complete? | -- | -- | |||||||||
15 | Replace the 3-2 SS valve assembly. Refer to Control and Shift Solenoids Replacement. Is the replacement complete? | -- | -- | |||||||||
16 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | System OK |
