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DTC codes / Honda codes / P1738

P1738 · HondaAutomatic Transmission System Malfunction

P1738 on Honda vehicles indicates that the transmission control module (TCM) has detected a general malfunction within the automatic transmission system, often related to the internal pressure switches or solenoid circuits. The TCM monitors these components for electrical faults or implausible signals and sets this code when the expected voltage or resistance falls outside the programmed range.

SystemPowertrain
Code typeHonda specific
SeverityMedium
Fix difficultyProfessional
AreaTransmission

Symptoms you may notice

  • Illumination of the malfunction indicator lamp (MIL) on the dashboard
  • Transmission may enter limp mode, limiting gear selection to a single gear
  • Harsh or delayed gear shifts
  • Slipping or flaring during acceleration
  • Often no symptoms besides the warning light

Common causes, most likely first

  1. Faulty transmission pressure switch (often 2nd, 3rd, or 4th gear switch)
  2. Damaged or corroded wiring harness to the transmission solenoids or switches
  3. Failed transmission solenoid pack
  4. Low or contaminated automatic transmission fluid (ATF)
  5. Internal transmission mechanical wear affecting hydraulic pressure
  6. Faulty transmission control module (TCM) or poor electrical connections

How to diagnose and fix it

  1. Check and top off the automatic transmission fluid (ATF) level and condition
  2. Perform a visual inspection of the transmission wiring harness and connectors for damage or corrosion
  3. Use a scan tool to read transmission-specific diagnostic trouble codes (DTCs) and freeze frame data
  4. Test the resistance of the pressure switches and solenoids according to the Honda service manual
  5. Replace faulty pressure switches or solenoids as needed
  6. Clear the codes and perform a relearn procedure if required
  7. If the code persists, diagnose internal transmission hydraulic issues or the TCM

Before replacing the transmission

  • A loose or corroded ground connection at the transmission can cause intermittent P1738 without any faulty components.
  • The code often sets due to a failing pressure switch that is inexpensive to replace, so avoid assuming the entire transmission needs overhaul.
  • Honda TCMs are sensitive to voltage fluctuations; a weak battery or charging system issue can trigger this code.
  • After repairs, the TCM may require a relearn procedure to clear the code and restore proper shift quality.
  • P1738 can be stored alongside other transmission codes like P0715 or P0750, which may point to a specific circuit fault.

Can I keep driving with P1738?

If the vehicle is in limp mode or shifting poorly, avoid driving at high speeds or under heavy load and seek service promptly. Continuing to drive with transmission issues can lead to further damage and higher repair costs.

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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