DTC P0973 Shift Solenoid 1 (SS1) Control Circuit Low
P0973 - Shift Solenoid 1
Circuit Description
Shift Solenoid 1 (SS1) is a normally closed solenoid used to properly position the C1 and C2 latch valves in forward ranges. The TCM commands the solenoid ON to supply control main pressure to the C1 and C2 latch valves. When solenoid SS1 is commanded OFF, control main pressure is relieved from the C1 and C2 latch valves.
The TCM sends control current to solenoid SS1 from High Side Driver 2 (HSD2) via wire 171. HSD2 is continuously ON unless the TCM detects a fault condition. The TCM energizes SS1 by switching the solenoid’s Low Side Driver (LSD) ON. Wire 151 completes the circuit between SS1 and its LSD. DTC P0973 indicates that the TCM has detected a short-to-ground or open circuit condition in the low side of SS1 electrical circuit.
Conditions for Running the DTC
• The components are powered and ignition voltage is greater than 9V and less than 18V (12V TCM) or greater than 9V and less than 32V (24V TCM).
• TCM initialization is in process or engine speed is greater than 200 rpm and less than 7500 rpm for 5 seconds.
Conditions for Setting the DTC
DTC P0973 sets when the TCM detects a short-to-ground or open condition in the SS1 return circuit for more than 125 milliseconds.
Actions Taken When the DTC Sets
When DTC P0973 is active, the following conditions occur:
• The CHECK TRANS light illuminates.
• DTC is stored in TCM history.
• Hydraulic default (SOL OFF) is commanded. The shift selector position and hydraulic state of latch valves determines the range attained.
Conditions for Clearing the DTC/CHECK TRANS Light
Use the Allison DOC™ For PC–Service Tool to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without failure.
Diagnostic Aids
• DTC P0973 indicates a short-to-ground or an open condition in the electrical circuit for the SS1 solenoid.
• You may have to drive the vehicle in order to experience a fault. Use the data obtained from failure records to determine transmission range and/or certain vehicle operating variables such as temperature, run time etc. This data can be useful in reproducing the failure mode when DTC was set.
• Inspect the wiring for poor electrical connections at the TCM and transmission connector. Look 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
• Inspect OEM wiring harness routing, look for possible contact points where chafing could occur leading to an open or short circuit condition. Moving parts on the vehicle could be contacting the harness; this includes parking brake drum, suspension components, etc.
• When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
• Advanced Troubleshooting (requires a frequency-capable digital multimeter, if available), measure solenoid LSD functionality as follows:
1. Install TCM breakout harness adapter J 47275 between the 80-way connectors of the TCM and OEM
harness.
2. Set up a frequency-capable digital multimeter, such as Fluke 87, to monitor frequency by selecting the VOLTS-DC scale and pressing the HERTZ button once.
3. Connect the RED test lead to the solenoid low side pin at TCM breakout harness adapter J 47275. Connect the BLACK test lead to the isolated ground pin.
4. Use Allison DOC™ For PC–Service Tool solenoid test function to command the solenoid ON and OFF.
5. Frequency should read in the KILOHERTZ range when the driver is commanded ON. Frequency
should read 0 hertz when the driver is commanded OFF. NOTE: A 1000 hertz test pulse may be
present in the SS1 circuit.
#Test Description
This DTC requires the use of the J 47275 TCM Breakout and J 47279 Transmission Breakout. The numbers below refer to step numbers on the diagnostic table.
2. Tests for the proper ignition voltage.
→Install the Allison DOC™ For PC–Service Tool.
→Start the Engine.
→Record the failure records.
→Monitor ignition voltage. Is the voltage within the specified values? 9–18V for 12V TCM, and 18–32V for 24V TCM.
3. Tests for an active DTC.
→Clear the DTC.
→Start the Engine and test drive the vehicle.
→Attempt to duplicate the same conditions observed in the failure records (range attained, temperature, etc.). NOTE: This DTC detects a short-to-ground or open condition in the SS1 electrical circuit. Did DTC P0973 return?
4. Tests for the OEM harness for an excessive voltage drop caused by an open condition in either wire 171 or wire 151 of the OEM chassis harness.
→Turn ignition OFF.
→Install J 47275 TCM Breakout between the OEM and TCM 80-way connectors.
→Install J 47279 Transmission Breakout between the OEM and transmission 20-way connectors.
→Turn ignition ON, leave engine OFF.
→Using Allison DOC™ For PC–Service Tool enter solenoid test mode and command solenoid SS1 ON. Read More: Solenoid Test using ALLISON DOC Software (ALLISON Transmission).
→Determine the voltage drop in the high side of the SS1 circuit as follows:
• At J 47275-1 TCM Overlay, measure voltage between pin 71 and an isolated ground.
• At J 47279-1 Transmission Overlay, measure voltage between pin 6 and ground.
• Subtract the two voltage measurements to obtain the voltage drop in the circuit.
→Determine the voltage drop in the low side of the SS1 circuit as follows:
• At J 47275-1 TCM Overlay, measure voltage between pin 51 and an isolated ground.
• At J 47279-1 Transmission Overlay, measure voltage between pin 10 and ground.
• Subtract the two voltage measurements to obtain the voltage drop in the circuit. NOTE: A voltage drop of more than 0.5V across either circuit indicates an excessive voltage loss in the OEM harness. Did either high-side or low-side voltage drop exceed 0.5 VDC?
5. Tests for wire-to-wire shorts or a short-to-ground condition in wire 151.
→Turn ignition OFF.
→Disconnect the TCM 80-way connector.
→Install the OEM-side of the 80-way connector to the J 47275 TCM Breakout. Leave the TCM disconnected.
→Disconnect the transmission 20-way connector.
→Inspect the routing of wire 151 in the chassis harness between the TCM and the transmission connector.
→At J 47275-1 TCM Overlay, test for wire-to-wire shorts between pin 51 and all other pins in the 80 way connector. Were any wire-to-wire shorts or shorts-to-ground found?
7. Tests for wire-to-wire shorts or a short-to-ground or an open in the internal transmission harness.
→Turn ignition OFF.
→Install J 47279 Transmission Breakout to the transmission 20-way connector. Leave the OEM harness disconnected.
→Using a DVOM, test for wire-to-wire shorts between pin 10 and all other pins in the 20-way connector.
→Test for an open between pins 6 and 10. NOTE: The resistance value between pins 10 and 6 will read normal solenoid resistance. The resistance value between pins 10 and 4, between pins 10 and 5, and between pins 10 and 9 will be twice normal solenoid resistance. Refer to Solenoid Resistance chart for these values (4.0 to 7.8 ohms). Were any wiring defects found?
8. Remove the hydraulic control module assembly.
→Disconnect SS1 from the internal harness.
→Inspect the internal harness for wire-to-wire shorts. Were any wiring defects found?
→Replace the internal wiring harness. Is the replacement complete?
→Replace SS1. Is the replacement complete? NOTE: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM.
To verify the repair:
1. Clear the DTC.
2. Drive the vehicle under normal operating conditions.
Did the DTC return?
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