P0740

What the Code Means

Code P0740 points to a fault in the torque converter clutch (TCC) solenoid circuit. The transmission control module (TCM) activates the lockup solenoid in 4th gear (D4) based on vehicle speed signals and input from the engine control module (ECM). When activated, the lockup clutch engages, giving a 1:1 speed ratio between the input shaft and the torque converter. Lockup is inhibited when ATF temperature is low. The code sets when the TCM detects an incorrect voltage drop while the solenoid is operating.

Symptoms

• Check Engine light on (Engine Light ON)
• Transmission shift shock
• Vehicle may not shift into highest gear

Diagnosis and Repair

Step 1: Check Transmission Fluid Level and Condition

Check the ATF level and condition. A low level or contaminated fluid can cause the solenoid to work incorrectly.

Step 2: Inspect Wiring and Connectors

Check the torque converter clutch solenoid harness and connectors for opens or shorts.

Step 3: Check Solenoid Resistance

Measure the solenoid resistance with a multimeter. The nominal values depend on the vehicle model.

Step 4: Replace the Solenoid

If faulty, replace the torque converter clutch solenoid (BMW part number 24117575279).

Step 5: Clear Codes and Test Drive

After the repair, clear the fault codes and take a test drive to verify.

Secondary Damage

Ignoring the code can prevent the torque converter from locking up, which causes transmission fluid overheating, accelerated wear on the friction plates and brake bands, and eventually transmission failure. You may also see lower fuel economy and degraded drivability.