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DTC codes / Honda codes / P1758

P1758 · HondaTCM A/T Lockup Solenoid Valve "B" Fault

P1758 on Honda vehicles means the Transmission Control Module (TCM) has detected an electrical fault in the lockup solenoid valve 'B' circuit inside the automatic transmission. The TCM monitors the solenoid's current draw and response time, and when the signal falls outside the expected range it commands the torque converter clutch to stay unlocked and stores this code.

SystemPowertrain
Code typeHonda specific
SeverityMedium
Fix difficultyProfessional
AreaTransmission

Symptoms you may notice

  • The check engine light or transmission warning light illuminates on the dashboard.
  • The torque converter clutch fails to engage, causing higher engine rpm at highway cruising speeds.
  • Poor fuel economy on the highway because the engine is not directly coupled to the transmission.
  • Slightly elevated transmission fluid temperature during sustained highway driving.
  • Harsh or delayed engagement when shifting from park or neutral into drive.
  • Often no symptoms besides the warning light, especially if the fault is intermittent.

Common causes, most likely first

  1. Failed lockup solenoid valve 'B' inside the transmission valve body due to wear or contamination.
  2. Damaged or corroded wiring harness connector at the transmission solenoid pack.
  3. Open or shorted wire in the lockup solenoid 'B' circuit between the TCM and the transmission.
  4. Contaminated automatic transmission fluid (ATF) causing solenoid sticking or poor electrical contact.
  5. Internal valve body wear or debris blocking the lockup solenoid hydraulic circuit.
  6. Faulty TCM driver circuit for the lockup solenoid, though this is less common.
  7. Poor ground connection for the transmission solenoid circuit.

How to diagnose and fix it

  1. Check the automatic transmission fluid level and condition; top off or replace if contaminated.
  2. Inspect the transmission solenoid pack connector for corrosion, loose pins, or damaged wiring.
  3. Measure the resistance of lockup solenoid valve 'B' at the solenoid pack connector and compare to Honda specifications.
  4. Test the wiring harness for continuity and short-to-ground between the TCM and the solenoid connector.
  5. If resistance is out of spec, replace lockup solenoid valve 'B' and reset the TCM.
  6. Clear the code and perform a road test to verify the torque converter clutch engages properly.
  7. If the code returns after electrical checks, inspect the valve body for wear or debris and service or replace as needed.

Lockup solenoid faults that fool technicians

  • A contaminated or degraded automatic transmission fluid is a frequent root cause of lockup solenoid codes on Hondas, and a fluid service alone can sometimes resolve the issue.
  • The lockup solenoid 'B' circuit often shares a connector with other solenoid circuits, so a single corroded pin can set multiple codes and mislead diagnosis.
  • Intermittent P1758 codes that appear only after the transmission reaches operating temperature often point to a failing solenoid coil rather than a wiring fault.
  • Some Honda models use a linear solenoid for lockup control, and its resistance changes with temperature, so testing a cold solenoid can give a false pass.
  • A failing lockup solenoid can cause torque converter clutch shudder that drivers mistake for engine misfire, leading to unnecessary ignition repairs.

Can I keep driving with P1758?

You can usually drive the vehicle with P1758 stored, but avoid sustained highway speeds and heavy acceleration because the torque converter clutch will not engage, which raises transmission fluid temperature. Have the fault diagnosed soon to prevent secondary damage to the transmission.

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 Honda vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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