WORKHORSE CUSTOM CHASSIS
Service Manual
Automatic Transmission – Allison
2007 W Series
© 2006 Workhorse Custom Chassis — All Rights Reserved
SECTION
7.2
PAGE
383
2007 W Series Chassis
WSM082106
DTC P0978
Step
Action
Value
Yes
No
11
Perform the following procedure in order to verify the repair:
1. Clear the DTC.
2. Drive the vehicle under normal operating conditions.
3. Select Specific DTC.
4. Enter DTC P0978.
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?
—
Go to Diagnostic
Trouble Code
(DTC) List -
Vehicle
System OK
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.
