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DTC codes / Nissan codes / P1682

P1682 · NissanA/T FI Signal A High Input

P1682 on a Nissan means the Transmission Control Module (TCM) has detected an abnormally high voltage on the Automatic Transmission (A/T) Fuel Injection (FI) signal circuit, which is the communication line between the TCM and the Engine Control Module (ECM). The TCM expects a specific voltage range on this signal wire, and a reading above the upper threshold triggers the code.

SystemPowertrain
Code typeNissan specific
SeverityMedium
Fix difficultyProfessional
AreaComputer and output circuits

Symptoms you may notice

  • Illuminated Check Engine Light or Service Engine Soon light on the dashboard.
  • Often no symptoms besides the warning light, especially if the fault is intermittent.
  • Harsh or delayed transmission shifts, or the transmission may enter limp mode.
  • Reduced engine performance or poor fuel economy due to compromised ECM-TCM communication.
  • In some cases, the engine may stall or hesitate during acceleration.
  • The transmission may fail to downshift properly when passing or climbing hills.

Common causes, most likely first

  1. Damaged or chafed wiring harness between the TCM and ECM, causing a short to voltage on the FI signal circuit.
  2. Corroded or loose electrical connectors at the TCM or ECM, leading to high resistance or intermittent voltage spikes.
  3. Faulty Transmission Control Module (TCM) internal circuitry driving the signal line high.
  4. Failed Engine Control Module (ECM) output driver affecting the shared communication line.
  5. Aftermarket electrical accessories improperly tapped into the FI signal circuit, introducing voltage.
  6. Water intrusion into the TCM connector or harness, causing corrosion and voltage irregularities.
  7. Poor ground connection for the TCM or ECM, causing reference voltage offsets.

How to diagnose and fix it

  1. Connect a scan tool and record all stored codes and freeze-frame data to confirm P1682 is the primary fault and not a secondary code.
  2. Visually inspect the TCM and ECM connectors for corrosion, loose pins, or water intrusion, and clean or repair as needed.
  3. Disconnect the battery and perform a continuity and voltage drop test on the FI signal wire between the TCM and ECM to check for shorts to voltage or opens.
  4. Wiggle-test the wiring harness while monitoring live data for the FI signal voltage to identify intermittent faults.
  5. Check for aftermarket accessories tapped into the circuit and remove or repair any improper connections.
  6. If wiring and connectors are good, substitute a known-good TCM and recheck for the code; replace the TCM if the fault persists.
  7. Clear codes and perform a road test to verify the repair and ensure the transmission operates correctly.

Hidden causes of P1682 on Nissan

  • A weak or failing battery or charging system can cause voltage spikes that mimic a high FI signal, so always check battery voltage and alternator output before condemning the TCM.
  • The FI signal circuit is shared with other sensors on some Nissan models, so a fault in a related component can set P1682 without any issue in the TCM itself.
  • Intermittent P1682 codes often stem from a chafed wire near the transmission bell housing or exhaust heat shield, which is easily missed during a visual inspection.
  • Aftermarket remote starters or alarm systems improperly wired into the CAN bus or signal circuits are a common cause of unexplained high-voltage codes on Nissans.
  • Do not replace the TCM based solely on P1682; always perform a thorough circuit test first, as the code can be set by a simple loose ground or corroded connector.

Can I keep driving with P1682?

You can usually drive the vehicle short distances to a repair shop, but avoid aggressive acceleration or heavy loads because the transmission may shift harshly or enter limp mode. If the vehicle exhibits severe drivability issues or stalls, stop driving and have it towed 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 Nissan vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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