P0743

ALLISON AUTOMATIC TRANSMISSION

DTC P0743

DTC P0743 Step 1 - 5:

DTC P0743 Step 6 - 11:

Circuit Description for Allison Automatic Transmission

Important: DTC P0743 was previously P1860.

The torque converter clutch solenoid, solenoid F. is a pulse width modulated solenoid. Pulse Width Modulation (PWM) occurs when the signal from the Transmission Control Module (TCM) to a solenoid is modulated at an established frequency, causing the steel check ball in the solenoid to rapidly open and close the solenoid passage. This serves to vary the output fluid pressure.

DTC P0743 is a type B DTC.

Conditions for Running the DTC
^ The components are powered and ignition voltage is greater than 9V and less than 18 V.
^ Engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds.

Conditions for Setting the DTC
DTC P0743 sets when the TCM detects an open circuit, a short to power, or a short to ground in the solenoid F circuit for 6 seconds.

Action Taken When the DTC Sets
^ The TCM illuminates the malfunction indicator lamp (MIL during the second consecutive trip in which the Conditions for Setting the DTC are met.
^ DTC P0743 will be stored in the TCM history.
^ The TCM inhibits TCC engagement.
^ The TCM freezes shift adapts (DNA).
^ Reverse operation is disabled.

Conditions for Clearing the MIL/DTC
A scan tool can clear the code 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
^ Inspect the wiring for poor electrical connections at the TCM. 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
^ 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 fault.
^ Solenoids are sensitive to battery voltage spikes and poor ground connections.

Test Description
The numbers refer to the step numbers on the diagnostic table.
2. This step tests the system voltage.
3. This step tests the command from the TCM to solenoid F.
4. This step tests the wiring harness for opens/shorts.
5. This step tests the internal wiring harness
6. This step tests the resistance at solenoid F.