DTC P0960 Pressure Control Solenoid Main Mod Control Circuit Open

P0960 - Pressure Control Solenoid Main Mod

Circuit Description

Pressure control solenoid Main Mod solenoid is a normally closed solenoid used to modulate the transmission main pressure schedule. The TCM commands the solenoid ON when specific transmission and Engine conditions are met. When the Main Mod solenoid is commanded ON, pressure is routed to the main regulator valve lowering the main pressure schedule.

The TCM sends control current to the Main Mod solenoid from High Side Driver 1 (HSD1) via wire 111. HSD1 is continuously ON unless the TCM detects a fault condition. The Transmission Control Module (TCM) regulates the amount of current to the Main Mod solenoid by switching the Main Mod solenoid’s Low Side Driver ON and OFF. Wire 174 completes the circuit between the Main Mod solenoid and its Low Side Driver (LSD). DTC P0960 indicates that the TCM has detected an open condition in the Main Mod solenoid electrical circuit. The open condition may exist in the high side (wire 111) or low side (wire 174).

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 P0960 sets when the TCM detects an open circuit on the Main Mod solenoid return circuit for more than 2 seconds.

Actions Taken When the DTC Sets

When DTC P0960 is active, the following conditions occur:

• The CHECK TRANS light illuminates.

• DTC is stored in TCM history.

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 P0960 indicates an open in the electrical circuit for the Main Mod solenoid. In addition to the Main Mod solenoid, HSD1 also supplies power to Pressure Control Solenoids 4 (PCS4) and PCS6. If DTC P0960 is accompanied by DTC P2718 (PCS4 open circuit) and/or DTC P2812 (PCS6 open circuit), the open is most likely in the high side of the circuit.

• 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.

#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 an open condition in the Main Mod solenoid electrical circuit. Did DTC P0960 return?

4. Tests the OEM harness for an excessive voltage drop caused by an open condition in either wire 111 or wire 174 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 ON the ignition, leave engine OFF.

→Using Allison DOC™ For PC–Service Tool, enter solenoid test mode and command the Main Mod solenoid ON.

→Determine the voltage drop in the high side of the Main Mod solenoid circuit as follows:

• At J 47275-1 TCM Overlay, measure voltage between pin 11 and an isolated ground.

• At J 47279-1 Transmission Overlay, measure voltage between pin 1 and isolated ground.

• Subtract the two voltage measurements to obtain the voltage drop in the circuit.

→Determine the voltage drop in the low side of the Main Mod solenoid circuit as follows:

• At J 47275-1 TCM Overlay, measure voltage between pin 74 and an isolated ground.

• At J 47279 Transmission Breakout, measure voltage between pin 8 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 0.5VDC?

6. Tests for an open condition in the transmission internal harness.

→Turn ignition OFF.

→Disconnect the OEM 20-way connector from J 47279 Transmission Breakout. Leave the transmission 20-way connector connected to the breakout.

→Using a digital multimeter (DVOM), measure the resistance between pin 1 and pin 8 of the transmission 20-way connector. Is the resistance within the specified value? (4.0 to 7.8 ohms).

7. Tests for the proper the Main Mod solenoid resistance.

→Remove the hydraulic control module assembly.

→Disconnect the Main Mod solenoid from the internal wiring harness.

→Using a DVOM, measure the Main Mod solenoid resistance at pins A and B. Is resistance within the specified values? (4.0 to 7.8 ohms).

→Replace the internal wiring harness. Is the replacement complete?

→Replace the Main Mod solenoid. 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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