Circuit Description
Shift solenoid 3 (SS3) is a normally closed (N/C) solenoid that provides control main pressure to stroke shift valve 3. The transmission control module (TCM) determines the proper solenoid command logic to move shift valve 3 to attain a particular range.
The TCM provides voltage to pressure control solenoid 2 (PCS2) and shift solenoid 1, 2, and 3 (SS1, SS2, and SS3) through a separate solid-state device called high side driver 2 (HSD2). The TCM uses a low side driver to switch SS3 ON and OFF.
Since the valve state, stroked or unstroked, is critical to providing the correct transmission range, the shift valve has a pressure switch, located in the pressure switch manifold, to provide feedback to the TCM about the position of the valve.
DTC P0978 is a type A DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0978 Shift Solenoid 3 (SS3) Control Circuit Open
Conditions for Running the DTC
| • | The components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts. |
| • | TCM initialization is in process or engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds. |
Conditions for Setting the DTC
DTC P0978 sets when the TCM detects an open condition in the SS3 return circuit for greater than 2 seconds.
Action Taken When the DTC Sets
| • | The TCM illuminates the malfunction indicator lamp (MIL). |
| • | If the failure occurs while in a forward range, a shift to 1st, 3rd or 5th range is made. |
| • | While diagnostic response is active, if the shift selector is moved to NEUTRAL, the transmission will shift to NEUTRAL. If the shift selector is moved to REVERSE, the transmission will shift to REVERSE. If the shift selector is moved to a forward range or to REVERSE and the transmission is compromised by overspeeding or direction change, the transmission will shift to NEUTRAL. |
| • | DTC P0978 is stored in TCM history. |
| • | Main modulation (MAIN MOD) is inhibited. |
| • | The TCM freezes shift adapts. |
| • | The TCM inhibits torque converter clutch (TCC) engagement. |
Conditions for Clearing the MIL/DTC
A scan tool can clear the code from TCM history. The TCM automatically clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without failure.
Diagnostic Aids
| • | Inspect the wiring for poor electrical connections at the TCM. Inspect for the following conditions: |
| - | A bent terminal |
| - | A backed-out terminal |
| - | A damaged terminal |
| - | Poor terminal tension |
| - | A chafed wire |
| - | A broken wire inside the insulation |
| • | When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change. |
| • | You may have to drive the vehicle in order to experience a condition. |
| • | DTC P0978, when set in combination with DTC P0964, P0972 and P0975, may indicate an open in the actuator supply voltage 2 circuit. |
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Value | Yes | No |
|---|---|---|---|---|
Schematic Reference: Automatic Transmission Controls Schematics | ||||
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 for reference. The Clear Info function will erase the data. Did the code become active? | Code Active | Go to Step 3 | Go to Testing for Intermittent Conditions and Poor Connections |
Is the voltage within the specified value when SS3 is commanded OFF? | B+ | Go to Step 4 | Go to Step 5 | |
4 | Command the solenoid ON. Did you get less than 5 volts with the solenoid commanded ON? | < 5.0 volts | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 10 |
5 |
Is the resistance within the specified value? | 22.0 ohms at 20°C (68°F) | Go to Step 7 | Go to Step 6 |
6 |
Is the solenoid resistance within the specified value? | 22.0 ohms at 20°C (68°F) | Go to Step 8 | Go to Step 9 |
7 | Test the SS3 circuit between the TCM and the AT inline 20-way connector for an open condition. Refer to Testing for Continuity . Did you find and correct the condition? | -- | Go to Step 11 | -- |
8 | Replace the AT internal wiring harness. Refer to Wiring Harness Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- |
9 | Replace the SS3. Refer to Control Valve Solenoid Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- |
10 |
Important: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM. Swap the TCM with a known good TCM to confirm diagnosis. Replace the TCM. Refer to Control Module References for replacement, setup and programming. Did you complete the replacement? | -- | Go to Step 11 | -- |
11 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | Go to Step 12 | Go to Step 2 |
12 | 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 | |
