P0979
DTC P0979
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 P0979 is a type A DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0979 Shift Solenoid 3 (SS3) Control Circuit Low
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 P0979 sets when the TCM detects a short to ground 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 P0979 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.
