DTC P0743. GMC Truck GMC K Sierra

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2004 🢒 GMC K Sierra - 4WD 🢒 Transmission/Transaxle 🢒 Automatic Transmission - Allison 🢒 DTC P0743

Circuit Description

The torque converter clutch (TCC) solenoid is a pulse width modulated (PWM) solenoid. Pulse width modulation 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 9.0 volts and less than 18 volts.

•	Engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds.

•	The TCC is commanded ON.

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 TCC PWM solenoid circuit for 1.5 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 TCM history.

•	The TCM inhibits TCC engagement.

•	The TCM freezes shift adapts.

•	REVERSE operation is disabled.

Conditions for Clearing the DTC

A scan tool can clear the code from TCM history. The TCM automatically clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without failure.

Diagnostic Aids

•	Inspect the wiring for poor electrical connections at the TCM. Inspect 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. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

•	You may have to drive the vehicle in order to experience a condition.

•	Solenoids are sensitive to battery voltage spikes and poor ground connections.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

This step tests the system voltage.

This step tests the resistance at the TCC PWM solenoid.

Step

Action

Value

Yes

Schematic Reference: Automatic Transmission Controls Schematics

Did you perform the Diagnostic System Check - Automatic Transmission?

Go to Step 2

Go to Diagnostic System Check - Automatic Transmission

Install the scan tool.
Start the engine.

Important:

•	Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the data.

•	This diagnostic table should only be used if the DTC is currently failing. If the DTC is not active, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems until the DTC becomes active.

Record the DTC Freeze Frame and Failure Records.
Clear the DTC.
Using the scan tool, measure ignition voltage.

Is voltage within the specified range?

9-18 V

Go to Step 3

Go to DTC P0562 for low voltage or DTC P0563 for high voltage

Turn the ignition OFF.
Disconnect the C2 connector (RED) at the TCM.
Using a DMM, measure the resistance between connector C2 terminal 29 and connector C2 terminal 32.

Is the resistance reading within the specified value?

10.5 ohms @ 20°C (68°F)

Go to Step 4

Go to Step 5

Turn the ignition OFF.
Disconnect the TCM connector C2 (RED).
Install the J 39700 breakout box and the J 43799 breakout box adapter. Do not connect the vehicle side C2 (RED) connector to the J 43799 .
Using a 12-volt unpowered test light, place the leads on terminals 29 and 32 of the J 39700 .
Turn the ignition ON, with the engine OFF.
Use the scan tool in Solenoid Test Mode to command TCC PWM solenoid ON and OFF.

Does the test lamp turn ON and OFF when commanded?

Go to Diagnostic Aids

Go to Step 11

Turn the ignition OFF.
Connect the C2 (RED) connector to the TCM.
Disconnect the transmission 20-way connector.
Turn the ignition ON, with the engine OFF. Additional DTCs may set.
Using a 12-volt unpowered test light, place the leads at the engine side of the transmission 20-way connector terminals J and S.
Use the scan tool in Solenoid Test Mode to command the TCC PWM solenoid ON and OFF.

Does the test lamp turn ON and OFF when commanded?

Go to Step 6

Go to Step 8

Turn the ignition OFF.
Using a DMM, measure the resistance between terminals J and S of the transmission 20-way connector.

Is the solenoid resistance within the specified value?

10.5 ohms @ 20°C (68°F)

Go to Diagnostic Aids

Go to Step 7

Remove the oil pan. Refer to Oil Pan Replacement .
Remove the internal wiring harness at the TCC PWM solenoid connector.
Using a DMM, measure the resistance of the TCC PWM solenoid.

Is the solenoid resistance within the specified value?

10.5 ohms @ 20°C (68°F)

Go to Step 9

Go to Step 10

Repair the engine wiring harness. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair

Go to Step 12

Replace the AT internal wiring harness. Refer to Wiring Harness Replacement .

Did you complete the replacement?

Go to Step 12

Replace the TCC PWM solenoid. Refer to Control Valve Solenoid Replacement .

Did you complete the replacement?

Go to Step 12

Important: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM.

Replace the TCM. Refer to Transmission Control Module Replacement .

Did you complete the replacement?

Go to Step 12

Perform the following procedure in order to verify the repair:

Clear the DTC.
Drive the vehicle under normal operating conditions.
Using the scan tool, monitor TCC slip speed. The TCC must engage/disengage when commanded.
Select Specific DTC.
Enter DTC P0743.

Has the test run and passed?

System OK

Go to Step 1