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DTC codes / Nissan codes / P1672

P1672 · NissanA/T FI Data Line Failure

P1672 on Nissan vehicles indicates a failure in the serial data communication line between the automatic transmission control module and the engine control module, specifically the A/T FI data line. The engine computer has detected that it cannot reliably exchange information with the transmission computer over this dedicated link, which is used for torque management and shift coordination.

SystemPowertrain
Code typeNissan specific
SeverityMedium
Fix difficultyProfessional
AreaComputer and output circuits

Symptoms you may notice

  • Illumination of the check engine light or service engine soon light on the dashboard.
  • Often no symptoms besides the warning light, with the vehicle driving normally.
  • Harsh or erratic automatic transmission shifting in some cases.
  • Reduced engine power or limp mode if the communication failure affects torque reduction requests.
  • Transmission may default to a fixed gear or fail to downshift properly during acceleration.
  • Intermittent stalling or poor idle quality if the data line corruption affects engine load signals.

Common causes, most likely first

  1. Damaged or corroded wiring in the A/T FI data line between the ECM and TCM, often due to chafing or rodent damage.
  2. Loose or corroded electrical connectors at the ECM or TCM harness.
  3. Failed transmission control module (TCM) internal communication circuit.
  4. Failed engine control module (ECM) communication driver for the A/T FI line.
  5. Poor ground connection for the TCM or ECM causing voltage reference shifts on the data line.
  6. Aftermarket electrical accessories improperly tapped into the data circuit causing interference.
  7. Battery or charging system issues leading to low voltage that disrupts serial data communication.

How to diagnose and fix it

  1. Verify battery voltage and charging system output, as low voltage can cause communication codes; recharge or replace battery if needed.
  2. Inspect the A/T FI data line wiring and connectors between the ECM and TCM for damage, corrosion, or loose pins; repair or repin as necessary.
  3. Check and clean the ground connections for the ECM and TCM to ensure proper reference voltage.
  4. Use a scan tool to perform a bidirectional communication test between the ECM and TCM to confirm the fault is active.
  5. If wiring and grounds are good, substitute a known-good TCM to see if the code clears, then replace if confirmed faulty.
  6. If the TCM does not resolve the issue, test or replace the ECM as the communication driver may be faulty.
  7. After repair, clear the code and perform a road test with scan tool monitoring to confirm the data line is functioning and no pending codes return.

Data line faults that mimic transmission failure

  • A P1672 code often sets without any driveability complaint, leading many to replace the transmission unnecessarily when the real issue is a chafed wire in the harness.
  • The A/T FI data line is a dedicated serial link, not the CAN bus, so a failure here will not always set U-codes and may be overlooked by generic scan tools.
  • Corrosion inside the TCM connector pins is a common cause on older Nissan models, especially in areas with road salt exposure.
  • Aftermarket remote starters or alarm systems tapped into the data line can introduce noise that corrupts communication and sets P1672 intermittently.
  • A weak battery or failing alternator can cause this code to set because the TCM and ECM may not communicate reliably during cranking voltage drops.

Can I keep driving with P1672?

You can generally continue driving if the vehicle runs and shifts normally, but avoid heavy acceleration or towing until the fault is repaired because the transmission may not receive proper torque reduction signals. If the transmission shifts harshly or enters limp mode, seek service promptly to prevent internal 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 Nissan vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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