Damaged or corroded wiring in the data line between the transmission control module (TCM) and engine control module (ECM); Loose or dirty electrical connectors at the TCM or ECM; Failed TCM or ECM, particularly if internal communication drivers are faulty; Poor ground connection for the TCM or ECM, causing voltage reference issues; Aftermarket electrical accessories improperly tapped into the data circuit; Battery or charging system problems causing low voltage and communication errors

DTC codes / Honda codes / P1672

P1672 · HondaA/T FI Data Line Failure

Q: What does code P1672 mean?

A/T FI Data Line Failure. P1672 on Honda vehicles indicates a failure in the serial data communication line between the automatic transmission (A/T) control module and the fuel injection (FI) engine control module. The engine computer has detected that the data stream carrying transmission information has been interrupted or is missing, which can affect shift quality and engine performance.

P1672 on Honda vehicles indicates a failure in the serial data communication line between the automatic transmission (A/T) control module and the fuel injection (FI) engine control module. The engine computer has detected that the data stream carrying transmission information has been interrupted or is missing, which can affect shift quality and engine performance.

SystemPowertrain

Code typeHonda specific

SeverityMedium

Fix difficultyProfessional

AreaComputer and output circuits

Symptoms you may notice

Check Engine Light or A/T warning light illuminated on the dashboard
Harsh or erratic shifting, including delayed or abrupt gear changes
Transmission may default to a limp-home mode with limited gear selection
Poor fuel economy or reduced engine power due to compromised integration
Often no symptoms besides the warning light, especially if the fault is intermittent

Common causes, most likely first

Damaged or corroded wiring in the data line between the transmission control module (TCM) and engine control module (ECM)
Loose or dirty electrical connectors at the TCM or ECM
Failed TCM or ECM, particularly if internal communication drivers are faulty
Poor ground connection for the TCM or ECM, causing voltage reference issues
Aftermarket electrical accessories improperly tapped into the data circuit
Battery or charging system problems causing low voltage and communication errors

How to diagnose and fix it

Inspect and clean the TCM and ECM connectors, checking for corrosion or loose pins
Perform a wiggle test on the wiring harness while monitoring live data to identify intermittent faults
Check continuity and resistance of the data line between the TCM and ECM using a wiring diagram
Verify battery voltage and charging system output to rule out low-voltage communication errors
Check and clean ground connections for the TCM and ECM
If wiring and connectors are good, swap in a known-good TCM or ECM to test communication
Repair or replace faulty wiring, connectors, or modules as needed and clear the code

Data line faults often misdiagnosed as transmission failure

A failed data line can mimic internal transmission problems, leading to unnecessary transmission replacement when the real issue is a chafed wire or corroded connector.
Intermittent P1672 codes often appear after engine washing or in humid conditions, pointing to water intrusion in connectors rather than a failed module.
Aftermarket alarms or remote starters tapped into the data bus can disrupt communication and set this code without any transmission symptoms.
The code may be stored alongside transmission range sensor or shift solenoid codes, but those should not be addressed until the data line integrity is confirmed.
A weak battery or failing alternator can cause voltage drops that corrupt data signals, setting P1672 even though the communication hardware is intact.

Can I keep driving with P1672?

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

Tools that help

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