P0740: Torque Converter Clutch Circuit Malfunction OBD-II Trouble Code

The presence of a P0740 DTC means that the ECU has detected a problem in the circuit that controls the torque convertor clutch solenoid. 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. 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.

Need a replacement transmission? Get an estimate for replacement transmissions and local installation. Look up your transmission model by vehicle make and model.

What Transmission Do I Have?

How Serious is the Code?

A P0740 diagnostic trouble code means that the ECU isn’t in complete control of the torque convertor, so drivability issues are sure to follow. 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.

Symptoms

Symptoms of a P0740 include:

• Check engine light
• Delayed, harsh or erratic shifts
• Engine stalling
• Transmission shudders/shakes when coming to a stop or accelerating
• Getting ‘stuck’ in a gear
• Vehicle won’t move when in gear
• Decreased fuel economy
• Overheated transmission

Causes

• Low transmission fluid level
• Dirty transmission fluid / filter
• Damaged wiring/connector
• Faulty torque convertor clutch solenoid / TCC solenoid
• Faulty torque convertor and/or clutch assembly
• Internal pressure issue
• Valve body issue
• TCM failure

How to Diagnose the Code?

To determine what is causing this DTC, a mechanic should first assess the condition of the transmission fluid, as dirty ATF can keep the TCC solenoid from working properly. The wiring and connectors should also be inspected for damage and corrosion. If no issues were found by this stage, then the torque convertor and TCC solenoid will have to be tested.

Wiring Harness

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.

TCC Solenoid

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. It’s not uncommon to assume that the torque convertor itself needs to be replaced/rebuilt, when it could just be a faulty TCC solenoid or dirty/contaminated transmission fluid.

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

Related Codes

P0741 – Torque Converter Clutch Circuit Performance or Stuck Off

P0742 – Torque Converter Clutch Circuit Stuck On

P0743 – Torque Converter Clutch Circuit Electrical

P0744 – Torque Converter Clutch Circuit Intermittent

P2769 – Torque Converter Clutch Circuit Low

P2770 – Torque Converter Clutch Circuit High

Need a replacement transmission? Get an estimate for replacement transmissions and local installation. Look up your transmission model by vehicle make and model.

What Transmission Do I Have?

Links To Diagnostic Codes

Links To Symptoms

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