Allison 1000 & 2000 Gen 4 Fault Codes: P0743 Torque Converter Clutch PWM Solenoid Circuit – Electrical

CIRCUIT DESCRIPTION:
The torque converter clutch (TCC) 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.

CONDITIONS FOR RUNNING THE DTC:
1. DTC P0122, P0123, P0716, P0717, P0721, P0722, or P0743 (previously P1860) is not active.
2. The components are powered and ignition voltage is greater than 9V and less than 18V (12V TCM) or greater 18V and less than 32V (24V TCM).
3. TCC is commanded on.
4. 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 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 or longer.

ACTION TAKEN WHEN THE DTC SETS:
1. DTC P0743 is stored in the TCM history.
2. The CHECK TRANS light illuminates on the second occurrence.
3. Reverse operation is disabled.

CONDITIONS FOR CLEARING THE DTC/CHECK TRANS LIGHT:
A Scan Tool may be used to 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 the DTC recurring.

DIAGNOSTIC AIDS:
If this DTC is cleared and does not return, but the TCC appears to be cycling, an intermittent circuit connection may exist that is not detected by the TCM since the circuit error must be present for more than 6 seconds. If a short to ground occurs at wire 229, the TCC will apply regardless of the range selected. A shudder in reverse may be caused by the intermittent apply or release of C5 clutch through the F solenoid valve.

Inspect the wiring for poor electrical connections at the TCM connector and the transmission main connector. Look for the following conditions:
1. A bent terminal.
2. A backed-out terminal.
3. A damaged terminal.
4. Poor terminal tension.
5. A broken wire inside the insulation.

Inspect the OEM wiring harness routing looking for possible contact points where chafing could occur. Moving parts on the vehicle could be contacting the harness. Items to check would include the parking brake drum, suspension components, transmission shift linkage, etc.

Inspect the internal transmission wiring harness for possible contact areas where chafing may occur.

When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change. It may be necessary to check for shorting to ground at individual wires within a harness to isolate an intermittent condition. Refer to wire check information.

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 where the DTC was set.

If the DTC appears to be temperature related, suspect a defective F solenoid. It is possible for a shift solenoid to be temperature sensitive causing resistance values to fluctuate. This may cause an intermittent DTC to be set.