OBD-II Code P1740 — What It Means & How to Fix It

What Does This Error Mean?

P1740 indicates a torque converter clutch (TCC) or overdrive solenoid performance problem. It is commonly seen on Toyota, Lexus, Nissan, and Honda vehicles. The TCC solenoid controls the lock-up clutch inside the torque converter. When this clutch does not engage or disengage as commanded, P1740 is set. Signs include the transmission hunting between gears, poor fuel economy, and high RPM at highway speeds.

Affected Models

Common in Toyota Camry, Corolla, and Sienna
Common in Toyota Tacoma and 4Runner
Common in Lexus ES and RX series
Seen in Nissan Altima and Maxima with automatic transmission

Common Causes

Faulty TCC solenoid or overdrive solenoid in the transmission valve body
Low or degraded transmission fluid causing inadequate solenoid hydraulic pressure
Clogged transmission fluid passages or dirty valve body
Damaged wiring or connector to the TCC solenoid
Faulty TCM not properly commanding the solenoid

How to Fix It

Check transmission fluid level and condition. Change the fluid and filter if it is dark, burnt, or overdue.

Dirty transmission fluid is a leading cause of solenoid performance faults and should always be done first.
Retrieve all TCM codes with a full-system scanner to confirm P1740 and check for companion codes.

Multiple solenoid codes often point to fluid pressure issues rather than individual solenoid failures.
Locate the TCC solenoid connector on the transmission and check for corrosion or damage.

The wiring harness runs along the transmission case and can chafe against the frame on trucks.
Test the TCC solenoid resistance with a multimeter. Typical resistance is 11 to 15 ohms — check factory specs for your model.

A solenoid reading open (infinite resistance) or shorted (near zero) is definitively failed and needs replacement.
If the solenoid tests in-spec, have a technician perform a live TCC engage/disengage test with a bi-directional scanner.

A solenoid can test good on a bench but still fail under actual hydraulic pressure — live testing is more accurate.

When to Call a Professional

TCC solenoid replacement is $60 to $200 in parts. Labor for valve body removal is 2 to 4 hours at $80 to $150 per hour. A transmission fluid and filter service first is $80 to $150 and sometimes resolves the issue. Full valve body replacement is $300 to $600 in parts.

Frequently Asked Questions

What does the torque converter clutch actually do?

The torque converter clutch (TCC) locks the engine and transmission together mechanically at highway speeds. This eliminates slippage in the torque converter, improving fuel efficiency. When it fails to lock properly, you get higher RPM than normal and worse fuel economy at highway speeds.

Can I drive with P1740?

You can drive short distances, but extended highway driving with a failing TCC wastes fuel and generates excess heat. Transmission overheating accelerates wear on all internal components. Get the issue diagnosed promptly.

Will a transmission fluid change fix P1740?

Sometimes yes — especially if the fluid is old and has lost its friction modifier properties. Fresh fluid can restore solenoid performance in mild cases. If the fluid is fresh and the code persists, the solenoid itself likely needs replacement.