What Does It Mean?
This diagnostic trouble code is defined when the engine management computer (ECM), also known as the powertrain control module (PCM) and also referred to as the engine control module (ECM), detects a failure in the electrical circuit of the torque converter clutch (TCC) solenoid, which is located inside the transmission.
An automatic transmission is not 100% efficient because it is a hydraulic coupling that connects the engine to the rest of the internal transmission components. The torque converter transfers power using hydraulic force and is internal to the transmission assembly. This power transfer results in excessive heat. The lock-up torque converter was designed to make the transmission more efficient at highway speeds and to control heat. The torque converter clutch is what locks the converter. Heat kills transmissions. This is why you hear that stop-and-go traffic is hard on an automatic transmission.
The torque converter clutch does not lock at these low speeds, so heat is generated. This clutch is controlled by an electrical solenoid. The torque converter clutch is locked, changing the hydraulic coupling into a mechanical coupling. This solenoid uses power and ground sent through a coil of wire that creates a magnetic field to pull or push a central metal rod. When the solenoid is energized or de-energized, it directs the flow of fluid through the transmission valve body.
Symptoms
Symptoms of a DTC P0743 may include:
Malfunction indicator lamp illumination (check engine light or service engine soon)
Stalling when coming to a stop after cruising speeds
Shudder upon takeoff
Shudder when stopping
Causes
Causes
Potential causes may include:
Low or dirty transmission fluid
Wiring/circuit issue shorted to power or ground
Faulty torque converter clutch (TCC) solenoid
Failure of the TCC assembly within the torque converter
Failed PCM/ECM/ECM
Note: This may well be an intermittent condition and may not reappear, so clear the code and continue monitoring.
Possible Solutions
You must first gather tools or borrow some (a rare phenomenon in mechanics because our tools are our livelihood and we don’t like lending our tools):
On-board diagnostic tool (OBD-II) – to retrieve the code; can be found at many parts stores, online, or many parts stores pull the code for free
Multimeter with resistance (or OHM) reading
Self-powered test light/probe (a Power Probe III). If you don’t have a power probe, a simple set of fused jumper wires and a test light will suffice
Wiring diagrams will be very helpful – you can get them in a Haynes manual or if you are friendly with the dealership or your local mechanic, they might be able to make a photocopy
TIP: Remember that in most cases, there is an internal transmission harness connecting the TCC solenoid and shift solenoids, so the wiring fault may only occur when the transmission is hot or cold. Or, when the vehicle is driven over bumps or during a turn. Make every effort to recreate it!
TIP: Before troubleshooting any transmission issue, ensure the engine is running perfectly! Address any other sensor codes or lean/rich codes first. There are many networked sensors that determine transmission shift programming. If one is “offline/faulty,” the ECM/PCM/ECM may trigger this code through the fault it sees on another sensor.
TIP: Many times, a simple fluid and filter change resolves minor transmission issues. There’s nothing to lose with a fluid and filter change.
Notice that I say change and not a fluid flush. A fluid flush on a high-mileage transmission can cause further damage. Also, for a slipping transmission, I recommend Lucas Oil Transmission Fix. I do not endorse the product and am not paid to use the name. But it works!
First, verify the condition/concern. In most cases, the TCC solenoid applies in overdrive when commanded by the PCM. TCC lock-up helps fuel economy and lowers transmission fluid temperature because the converter is locked (look up TCC operation for an in-depth insight as theory and operation are difficult to explain without getting too technical. With this explanation, one might get the deer in the headlights look).
In my case, my vehicle stumbled and nearly stalled at a light. Once verified, we can begin diagnosis.
Perform a general condition check of the fluid and check the level if everything is OK. Also, is the transmission shifting properly? Is the engine running correctly? Most transmission problems are misdiagnosed due to poor engine performance. Remember, power flow starts at the engine and goes through the transmission, then to the drivetrain.
Next, check the external transmission harness and connectors. Also check your fuses and ensure the transmission case is grounded AND connected to the battery.
Proceed to locate the appropriate wires corresponding to the torque converter clutch. In most cases, this will be two wires; one for ground and one for positive. Apply power and ground and listen for the solenoid to click.
If the solenoid does not click, proceed to check continuity through the solenoid and continuity to and from the corresponding wires to and from the sensor. The solenoid should have a low ohm reading (0.02 to 0.05), this will vary by manufacturer, so check your reading against a factory service manual or equivalent. The wires should also have a low ohm reading. Also ensure none of the wires are shorted to ground or power.
If the wires check out and the solenoid clicks. There may be a PCM issue, but I advise pulling the transmission pan and carefully inspecting the TCC solenoid for debris. Any small amount of debris will cause the solenoid to short and make the computer think it is applied. Or, if it is metal debris, it will stick to the solenoid and prevent it from disengaging. This was the problem in my case.
I would also advise getting the latest calibration for your vehicle’s computer (PCM) from your dealership. Manufacturers constantly release new, improved software. There may be a revised calibration to address this code. Especially if it is intermittent.
Finally, if everything is OK and you go ahead and replace the PCM, remember it must be programmed for the vehicle. In many cases, there is an anti-theft device in the key and with that the keys need to be programmed. Think dealership or mechanic.
If all else fails and you are at your wit’s end, there may be an issue with the clutch inside the torque converter. This will most likely be evident if you feel slipping when the transmission locks up in overdrive. The fluid may also smell burnt or be completely black.Good luck! In my case, I am a Ford-trained technician and due to my experience, I simply pulled the transmission pan and took a look at the solenoid and found my problem right away. This is a common issue on higher-mileage transmissions.