Code
P1671
INFINITI
P — Powertrain
A/T FI Data Line No Signal
AI status
Completed
Completed
100%
Causes
- Open or shorted FI/data communication wiring between transmission and ECU/TCM
- Corroded, loose or damaged connector at the transmission control module (TCM) or ECU
- Blown fuse or loss of power/ground to the TCM or related module
- Water intrusion or mechanical damage to the harness near the transmission
- Failed TCM or ECU (module internal fault)
- Intermittent connection due to broken wire, pin terminal or poor repair
Symptoms
- Malfunction Indicator Lamp (MIL) or transmission warning light illuminated
- Transmission may default to limp/limited shift mode or fail to shift properly
- Loss of transmission-related data on scan tool (no live data from A/T module)
- Other modules report communication-related DTCs (U-codes)
- Possible rough or fixed gear selection, reduced drivability
What to check
- Read all stored DTCs and freeze frame data with a capable scan tool; note any U-codes and P0700
- Attempt to communicate with the transmission control module (TCM) via scan tool — check for live data or module presence
- Visually inspect connectors and harness along the transmission-to-ECU route for corrosion, bent pins, water ingress, or damage
- Check fuses and relays that supply power to the TCM and related circuits
- Wiggle test the harness with key ON while monitoring for changes in communication
- Consult vehicle wiring diagram to identify FI/data line routing, connectors and related grounds
Signal parameters
- Type: digital communication/data line (module-to-module data frames)
- Idle/expected behavior: data line should show active data frames (toggling) with key ON/engine running; exact idle voltage depends on protocol (single-wire or differential CAN-type)
- Typical checks: presence of voltage/pulses on the data line with a scope or diagnostic tool; continuity between module connectors; no short to battery or ground
Diagnostic algorithm
- Document all DTCs (including U-codes) and attempt to communicate with the TCM using a factory-level or bi-directional scan tool.
- Inspect connectors at the transmission and control module(s). Unplug, inspect terminals and pins for corrosion, bent pins, or pushed-out terminals; reconnect and secure.
- Verify power and ground to the TCM: check relevant fuses, ignition-switched power, and ground points per wiring diagram.
- With ignition ON, monitor the FI/data line with a diagnostic scope or logic probe. Verify presence of data pulses or expected idle voltage. If no activity, proceed to trace the line.
- Test continuity of the data line between transmission connector and the receiving module(s). Check for short to ground or battery voltage using multimeter/ohmmeter.
- If an open/short or connector fault found, repair or replace damaged wiring or connectors, then recheck communication.
- If wiring and power/ground are good but no data, consider module failure. Verify with a known-good TCM or bench test per service procedures before module replacement.
- Clear DTCs and perform a test drive/retest to confirm repair. Monitor for recurrence and related codes.
Likely causes
- Damaged/loose connector at the transmission or TCM
- Open or short in the FI/data line wiring (rodent damage, chafing)
- Blown fuse or missing power/ground to transmission control module
- Failed transmission control module (less likely than wiring/connectors)
Fault status
Status
A/T FI data line no signal — transmission control data unavailable (communication line open/shorted or module not sending).
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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