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Home / DTC / P0742 — Torque Converter Clutch Circuit Stuck On

P0742 — Torque Converter Clutch Circuit Stuck On

Detailed page for trouble code P0742.

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Code

P0742

MERCEDES-BENZ P — Powertrain

Torque Converter Clutch Circuit Stuck On

Brand: MERCEDES-BENZ
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Short to battery/constant power on TCC control circuit
  • Short to ground in TCC wiring or connector
  • Failed or stuck TCC solenoid
  • Valve body or apply valve sticking (mechanical)
  • Internal transmission wear or debris causing clutch to remain applied
  • Poor connector connection or corrosion at solenoid/TCM

Symptoms

  • Malfunction Indicator Lamp (MIL) / Transmission warning light illuminated
  • Torque converter behaves as if locked at inappropriate times (lurching or bucking)
  • Engine may stall when coming to a stop or during low-speed maneuvers
  • Harsh or delayed shifting, poor acceleration
  • Transmission may run hot; burning smell in severe cases
  • Possible limp-home mode or reduced performance

What to check

  • Retrieve freeze frame and live data with a capable scan tool; note TCC commanded vs actual status and any transmission temperature data
  • Visual inspection of TCC solenoid connector(s) for corrosion, bent pins, water intrusion or damaged insulation
  • Measure supply voltage and ground at the solenoid connector with key on/engine running
  • Check solenoid coil resistance against manufacturer spec (bench or in-circuit)
  • Back-probe solenoid while commanding TCC on/off to verify control signal (voltage or PWM) follows command
  • Inspect transmission fluid level and condition (contaminated or burnt fluid)

Signal parameters

  • Typical TCC solenoid coil resistance: manufacturer-specific — commonly in the low single digits to tens of ohms (e.g., ~5–30 Ω). Verify against Mercedes spec before replacing.
  • Control signal: switched 12V or ground-controlled circuit (some systems use PWM). When commanded OFF the control circuit should not supply continuous drive current; when ON the controller will supply voltage or PWM. Use scope to confirm duty cycle and voltage levels.
  • Expected connector supply voltage (key ON): battery voltage at fused feed; ground should be

Diagnostic algorithm

  1. Read and record all stored codes and freeze-frame data using a professional scan tool; clear codes and attempt to re-create the issue.
  2. Compare TCC command vs actual status in live data while road testing or during a transmission self-test. Note times when code sets (idle, load, shift points).
  3. Visually inspect connectors and harness along the TCC solenoid circuit for damage, chafing, water ingress, or rodent chewing. Repair any damage and re-test.
  4. With ignition ON (engine off), measure resistance of the TCC solenoid coil. If resistance is out of spec, remove and bench-test/replace the solenoid.
  5. Back-probe the connector while commanding the TCC ON and OFF; verify the control module stops supplying current when commanded OFF. Use a scope if available to check for PWM and abnormal DC presence when OFF.
  6. If the solenoid is not being commanded but is powered, trace for a short to power (fused feed) or a wiring shorted to a constant 12V source. If solenoid is being commanded but not releasing, suspect mechanical sticking or valve body fault.
  7. If wiring and solenoid check good, inspect valve body for sticking apply valve or debris; replace or rebuild valve body as required per service manual.
  8. If electrical and mechanical checks pass, consider TCM/ECM software, calibrations or internal controller faults. Reflash or replace only after ruling out harness/solenoid/valve body issues.
  9. After repairs, clear codes and perform a full road test and scan-tool verification to ensure no recurrence.

Likely causes

  • TCC solenoid electrical short (stuck energized)
  • Wiring shorted to battery supplying constant power to solenoid
  • Solenoid stuck mechanically (sticking/plated) inside valve body
  • Corroded/loose connector at solenoid or TCM causing intermittent contact
  • Valve body bore or valve sticking due to contamination or wear

Fault status

⚠️ Status
TCM reports Torque Converter Clutch circuit stuck ON — clutch engaged when not commanded. MIL illuminated; transmission limp/reduced performance possible.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.5-3.5 hours

Similar codes

P0740 P0741 P0743 P0746
856

Browse 856 MERCEDES-BENZ manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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