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DTC codes / Honda codes / P1655

P1655 · HondaTMA or TMB Signal Line Fault

P1655 on Honda vehicles indicates that the powertrain control module (PCM) has detected a fault on the signal line for the Transmission Mainshaft Speed sensor A or B (TMA or TMB). The PCM monitors the expected voltage or signal pattern from these sensors and sets the code when the signal is missing, erratic, or out of range.

SystemPowertrain
Code typeHonda specific
SeverityMedium
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • Illumination of the check engine light or transmission warning light, often with no other symptoms
  • Harsh or delayed shifting, especially when the transmission is cold
  • Erratic or inconsistent shift points during acceleration
  • Transmission may enter limp mode, limiting gear selection
  • Speedometer fluctuation or inaccuracy (if the sensor also feeds the speedometer)
  • Poor fuel economy due to improper shift scheduling

Common causes, most likely first

  1. Faulty transmission mainshaft speed sensor (TMA or TMB)
  2. Damaged or corroded wiring harness or connector at the sensor
  3. Open or short circuit in the signal line between the sensor and PCM
  4. Metal debris or contamination on the sensor tip, disrupting the magnetic signal
  5. Internal PCM fault (rare but possible)
  6. Poor ground connection for the sensor circuit

How to diagnose and fix it

  1. Scan all modules for stored codes and freeze-frame data to confirm P1655 and identify which sensor circuit (TMA or TMB) is affected
  2. Visually inspect the sensor and its connector for damage, corrosion, or loose pins; clean and apply dielectric grease if needed
  3. Check the sensor resistance and signal output with a multimeter or oscilloscope according to Honda service information
  4. Inspect the wiring harness for continuity, shorts to ground, or shorts to power between the sensor and PCM
  5. If the sensor fails electrical tests, replace the faulty sensor and clear codes
  6. If wiring is faulty, repair or replace the affected section of the harness
  7. After repairs, perform a road test with the scan tool to verify the code does not return and shift quality is restored

Mainshaft Speed Sensor Faults Often Misdiagnosed

  • A common mistake is replacing the transmission or PCM before checking the sensor signal; always verify the sensor output with a scope or multimeter first.
  • The TMA and TMB sensors are often confused with the countershaft speed sensor; ensure you are testing the correct sensor for the code.
  • Debris on the sensor tip from normal wear can cause intermittent signal loss without any visible wiring damage, so removal and cleaning is a wise first step.
  • This code can be set by a poor ground connection at the transmission housing, which is often overlooked during diagnosis.
  • On some Honda models, a failing sensor may not trigger drivability symptoms until the transmission enters limp mode, so the code may be the only clue.

Can I keep driving with P1655?

If the vehicle drives normally, you can drive it to a repair shop, but avoid aggressive acceleration or heavy loads. If the transmission is in limp mode or shifting harshly, limit driving to a short distance to prevent further damage.

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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