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DTC codes / Nissan codes / P1901

P1901 · NissanTorque Converter Clutch Circuit Intermittent

P1901 on Nissan vehicles means the transmission control module (TCM) has detected an intermittent electrical fault in the torque converter clutch (TCC) solenoid circuit. The TCM monitors the circuit for expected voltage and current when commanding the clutch on or off, and it flags this code when the signal drops out or behaves erratically for a brief period rather than failing completely.

SystemPowertrain
Code typeNissan specific
SeverityMedium
Fix difficultyProfessional
AreaTransmission

Symptoms you may notice

  • The check engine light or transmission warning light illuminates, often with no other noticeable symptoms.
  • A slight shudder or vibration during light acceleration at steady highway speeds when the clutch tries to engage.
  • The engine may flare or rev slightly higher than normal during gentle acceleration as the clutch fails to lock.
  • Harsh or delayed engagement when shifting from park or neutral into drive, especially when cold.
  • Intermittent harsh downshifts or a feeling that the transmission is 'hunting' for the right gear.
  • Poor fuel economy on the highway because the torque converter clutch stays unlocked more often than it should.

Common causes, most likely first

  1. A failing torque converter clutch solenoid, where the internal coil becomes intermittent when hot or after many operating cycles.
  2. Damaged or chafed wiring in the transmission harness, often near the valve body connector or where the harness passes through the case.
  3. Corroded or loose pins at the transmission case connector or at the TCM connector, causing an intermittent open circuit.
  4. Contaminated transmission fluid (ATF) or a clogged solenoid screen that restricts flow and causes erratic solenoid operation.
  5. A sticking valve body spool valve or worn bore that prevents the solenoid from controlling clutch apply pressure consistently.
  6. Internal TCM driver circuit faults, though this is less common than harness or solenoid issues on Nissan units.

How to diagnose and fix it

  1. Scan all modules for stored and pending codes, and record freeze-frame data to see the exact conditions when P1901 set.
  2. Inspect the transmission fluid level and condition; dark or burnt fluid with debris points to internal wear and should be addressed before electrical diagnosis.
  3. Visually inspect the transmission harness and case connector for chafing, corrosion, or loose pins, and perform a wiggle test while monitoring solenoid command and feedback with a scan tool.
  4. Measure the TCC solenoid circuit resistance at the transmission connector and compare it to the Nissan specification for the specific transmission model.
  5. Check for voltage drops and shorts to ground or power on the TCC solenoid control circuit between the TCM and the transmission connector.
  6. If electrical checks pass, remove the valve body and inspect the TCC solenoid and its screen for debris, then test the solenoid on the bench for intermittent operation when heated.
  7. After any repair, clear the codes and perform a relearn or adaptation drive cycle as required for the Nissan transmission, then verify the code does not return.

What Nissan techs check before replacing the TCC solenoid

  • A loose or corroded ground strap between the engine and chassis can create intermittent voltage offsets that the TCM interprets as a TCC circuit fault, so always check grounds before condemning the solenoid.
  • On many Nissan transmissions, the TCC solenoid shares a power feed or ground path with other shift solenoids, so a fault in a neighbouring circuit can set P1901 without the TCC solenoid itself being defective.
  • Intermittent codes often appear only after the transmission reaches operating temperature, so a cold-vehicle resistance check can pass while the solenoid is still failing when hot.
  • Aftermarket transmission fluid that does not meet the Nissan Matic specification can cause solenoid sticking and intermittent TCC operation, mimicking an electrical failure.
  • A failing crankshaft position sensor or engine misfire can cause the TCM to disable TCC lockup and set related codes, so always check for engine-side faults before focusing solely on the transmission.

Can I keep driving with P1901?

You can usually continue driving short distances at moderate speeds, but avoid heavy towing or sustained highway driving because an unlocked or slipping torque converter clutch generates extra heat that can damage the transmission. If the transmission begins to shudder severely or slip, stop driving and have it inspected promptly.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Nissan vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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