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P0740Cars & SUVs
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P0740Torque converter clutch circuit malfunction

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Check soon

— A lockup clutch that slips generates heat fast and contaminates the fluid, which turns a solenoid job into a rebuild — repair within days.

What does this severity mean?

General guidance only — not a substitute for a professional inspection or official roadside / out-of-service criteria (e.g. CVSA OOSC) in your jurisdiction.

Part of system: Transmission control & ratio monitoring

Means the torque converter clutch circuit did not behave as commanded: either the solenoid circuit is electrically faulty or the converter never reached the slip ratio the controller expected at lockup. Separate those two possibilities by graphing engine speed against input or output shaft speed during a steady highway cruise. If engine RPM drops the expected two to four hundred when lockup commands and then creeps back up, the clutch is slipping mechanically. If nothing changes at all, measure solenoid resistance and command lockup with a bidirectional tool. Low, burnt, or contaminated fluid and a clogged filter cause far more of these codes than failed converters, so check fluid condition and level at operating temperature first. Continued driving with a slipping lockup clutch overheats the fluid and contaminates the entire transmission.

Parts that may be involved

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Vehicles often affected

High-mileage automatics with deferred fluid service, and towing vehicles that spend long stretches at part-throttle lockup, fail here most often.

Typical symptoms

  • Engine RPM staying high at highway cruise with no lockup
  • Shudder that feels like driving over rumble strips at light throttle
  • Transmission fluid temperature climbing on long runs
  • Slight RPM flare at the moment lockup should apply
  • Highway fuel economy dropping noticeably

Likely causes

  • Converter clutch solenoid electrically open or shorted
  • Converter clutch lining worn so lockup never holds
  • Fluid low, burnt, or contaminated, delaying apply pressure
  • Valve body bore wear bleeding off apply pressure
  • Case connector or harness corroded on the solenoid circuit

Recommended checks

  1. 1

    Graph engine RPM against shaft speed during a steady cruise

  2. 2

    Command lockup with a bidirectional tool and watch the RPM drop

  3. 3

    Measure solenoid resistance and inspect the case connector

  4. 4

    Check fluid level and condition at operating temperature

  5. 5

    Service the fluid and filter before any internal repair decision

DIY vs professional

DIY: fluid and filter service, external connector inspection. Pro: line pressure testing, valve body work, converter replacement.

See also

Content reviewed by a heavy-duty technician. About our editorial approach