In This Guide
- What Does P0740 Mean?
- Symptoms of P0740
- Common Causes of P0740
- How to Diagnose the P0740 Code?
- Common Mistakes When Diagnosing
- What Repairs Will Fix the P0740 Code?
- Codes Related to P0740
- Need more help with a P0740 code?
A torque converter clutch (TCC) circuit malfunction is what triggers trouble code P0740. All vehicles manufactured since 1996, regardless of make and model, may return this generic trouble code. Yet, different models may have varying steps for repairs and diagnosis. Below, we will get you started on remedying this issue.
What Does P0740 Mean?
P0740 indicates that there is an issue with the torque converter clutch circuit.
Situated between the transmission and the engine, the torque converter works to equalize the speed by multiplying the torque in order to optimize vehicle performance (increases fuel efficiency and reduces the transmission fluid temperature.
The transmission control module (TCM) controls the torque converter clutch (TCC). When disengaged, the TCC locks the converter shell to the turbine shaft – creating a 1 to 1 connection between the transmission and engine to prevent slippage. If the application of the clutch is abnormal (multiple times), then trouble code P0470 appears.
Symptoms of P0740
The driver could experience any of the following symptoms when a P0740 trouble code appears:
- Misfire-like symptoms, stalling at a stop, or other performance issues
- Harsh shifting
- Unable to shift in or out of a particular gear
- Reduced fuel economy
- Overheated transmission
- Illumination of the Check Engine light.
In some cases, there are no symptoms noticed by the driver
Common Causes of P0740
The P0740 trouble code is commonly caused by the following:
- Restricted hydraulic passages caused by dirty transmission fluid
- Damage in wiring harness, shorted or open circuit, or loose connection in transmission
- Valve body is defective
- Damaged torque converter or TCC
- Temperature sensor for the engine coolant is defective
- Torque converter lockup solenoid is defective
- Incorrect transmission fluid level
How to Diagnose the P0740 Code?
There are three main parts that you will want to test to diagnose the problem:
See if there are loose connections or damage in the wiring harness of the transmission. Find all connections between circuits and the appropriate power source by using the factory wiring diagram. A relay or fuse may power the transmission, and the transmission control module may trigger it.
At the TCM, power, and transmission connector, disconnect the transmission harness. By finding the right “+” and “-“ pins of the TCC solenoid, check for transmission internal wiring harness continuity.
Set a digital multimeter to the ohms scale to check the circuit resistance with the negative and positive leads connected to the right pins. You probably have a fault in the torque converter clutch solenoid or the internal harness if you get an over limit or extremely high resistance.
After removing the transmission harness plug, check the wiring in the case of the transmission and the torque converter clutch solenoid resistances. Depending on the make and model of your vehicle, the internal harness and solenoid may be one unit.
Place the negative and positive leads of your multimeter (set to the ohms scale) on the appropriate pins of the control circuit and TCC power. The resistance should be within the specifications set out by the manufacturer. If possible, inspect the TCC solenoid inside the transmission by removing the transmission oil pan if you get a reading that is OL or very high.
Transmission Control Module (TCM)
To determine what the actual feedback is at the TCM and if it is commanding the solenoid, you need to track the TCM using a scan tool since the TCC is only activated under specific driving conditions. To get a comfortable TCC engagement, the solenoid is controlled by the duty cycle normally.
Digital storage oscilloscopes or graphing multimeters set to the duty cycle will be needed to test if a signal is actually being sent by the TCM. The negative is probed to a good ground and the positive to the wiring harness that is plugged into the TCM. The TCM may be at fault when the cycle is intermittent or at 0 percent or 100 percent.
Common Mistakes When Diagnosing
The most common mistakes made when diagnosing P0740 is thinking that the problem is related to driveline issues, internal transmission issues, or engine misfire issues.
What Repairs Will Fix the P0740 Code?
There are several repairs that could potentially address the P0740 trouble code, including:
- Installing a brand new transmission
- Perform an overhaul of the transmission
- Powertrain control module replacement
- Replacing or adding transmission filter and fluid
- Replacing the clutch or torque converter
- Torque converter clutch solenoid replacement
Codes Related to P0740
The P0740 trouble code is similar to:
Need more help with a P0740 code?
Let us assist you if you are still having issues after reviewing the above guide. Comment below with the year, make, and model of your vehicle as well as the symptoms and code(s) you are getting.