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Mitsubishi Galant P0743: Meaning, Causes and Diagnosis

 

P0743 Mitsubishi Galant

P0743 is a generic OBD2 code that may appear on the Mitsubishi Galant. This indicates that your ECU/TCM has found a problem with the torque converter clutch solenoid.

It is a generic code (meaning it has the same definition for all cars and trucks). The repair steps will vary depending on the model year of your Galant and the type of transmission.


Definition: Torque Converter Clutch Circuit

Mitsubishi Galant P0743 Meaning

This is the definition of P0743, broken down into its two parts:

torque converter clutch

Your Galant uses a clutch in the torque converter to lock the engine and transmission together at highway speeds. When locked together, it allows for greater fuel economy, and the engine will run a few hundred RPM less than it would without it.

Modern vehicles have been using lock-up torque converters for over 30 years.

The torque converter clutch is controlled by the ECM/TCM and turns off when you slow the vehicle below a certain threshold, press the brake pedal, or if the vehicle downshifts.

Circuit

When your Mitsubishi Galant’s ECM/PCM detects a problem with the torque converter clutch circuit, it will store P0743 in its internal memory.

P0743 does not indicate whether the torque converter circuit voltage is too high or too low, only that the circuit signal is outside the normal operating range.

This broad definition means that there may be many potential causes (discussed below).


Mitsubishi Galant P0743 Symptoms

As P0743 is a transmission-related code, will not affect the operation of the engine. But it really can impact the way the transmission feels when you drive.

If the torque converter locks up when it shouldn’t, it can make driving your vehicle almost impossible. These are the most common symptoms:

  • Slightly higher RPM at highway speeds (converter does not lock up)
  • Stalls when stopped (inverter does not unlock)
  • Transmission overheating (any scenario)
  • Decreased MPG
  • Doesn’t move at all (this doesn’t usually happen)

Mitsubishi Galant P0743 Causes + Diagnosis

P0743 Diagnostic

These are the most common causes of P0743. They are listed emphasizing what you can check at home.

Check the transmission fluid (level and consistency)

Start by checking your Galant’s transmission fluid. A low transmission fluid level can cause a drop in line pressure and cause the torque converter lockup solenoid to malfunction.

The transmission fluid should be full and clean. If the fluid is black or shows signs of being burned, changing the fluid may be enough to eliminate P0776.

A clogged transmission filter can cause the pressure inside the transmission to drop as well.

Automatic transmission fluid has a very hard job. It has to cool, lubricate and transfer energy. It may go a long time without being changed, but if it overheats, it may be enough to cause P0743 in your vehicle.

Check if the wiring harness is damaged

Check the wiring harness that goes to your Galant’s torque converter lockup solenoid (if you can access it). Make sure the wiring harness has not been damaged by road debris. If it is damaged, repair it, clear the code, and check if P0743 appears again.

Lock Control Solenoid Test

The lockup control solenoid is responsible for engaging and disengaging the torque converter clutch. You can test it with a good multimeter. The following video will show you exactly how to do it.

Other causes

Here are some other problems known to cause P0743 on the Mitsubishi Galant:

  • Defective TCM/PCM
  • Bad torque converter
  • Internal transmission failure

Conclusion

P0743 is most likely caused by a wiring problem with the torque converter clutch solenoid, a wiring problem, or problems with the transmission fluid. Good luck repairing your Galant!

 

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