01 How to Schedule Your Automotive Maintenance • 02 The Dangers of Driving on Low Fuel: Risks and Consequences … • 03 Why Some Cars Are Cheap to Buy but Expensive to Maintain • 04 What Happens If You Ignore A Check Engine Light For Too Long • 05 Electric and Hybrid Vehicle Buying Guide: Everything You Ne… • 06 P0081, P0082, and P0083: Intake valve control solenoid circ… • 07 How to Clean Piston Ring Grooves: A Complete Guide • 08 The Mitsubishi Outlander PHEV: A Plug-in Hybrid SUV That Ch… • 09 What Happens When You Let Someone Else Drive Your Car and T… • 10 5 Things You Need to Know About Faulty Oxygen Sensors in Ca… •

DTC codes / Subaru codes / P1698

P1698 · SubaruEngine Torque Control Cut Signal Circuit Low Input

P1698 on a Subaru means the engine control module (ECM) has detected a low input voltage on the circuit that carries the engine torque control cut signal, which is the command used to momentarily reduce engine torque during automatic transmission shifts. The ECM expects to see a specific voltage on this signal line, and a reading below the acceptable threshold tells the computer that the circuit is shorted to ground or that the signal is not being generated correctly.

SystemPowertrain
Code typeSubaru specific
SeverityMedium
Fix difficultyProfessional
AreaComputer and output circuits

Symptoms you may notice

  • Illumination of the check engine light or malfunction indicator lamp (MIL) on the dashboard
  • Often no symptoms besides the warning light, especially if the fault is intermittent
  • Harsh or delayed automatic transmission shifts as torque reduction during shifts is compromised
  • Slight hesitation or stumble during acceleration when the transmission is changing gear
  • Reduced fuel economy or altered shift feel over time if the signal remains low
  • In rare cases, the transmission may enter a limp mode with limited gear selection

Common causes, most likely first

  1. Damaged or chafed wiring in the engine torque control cut signal circuit, often near the transmission bellhousing or engine harness
  2. Corroded or loose electrical connector at the transmission control module (TCM) or ECM
  3. Failed transmission control module (TCM) internal driver for the torque cut signal
  4. Failed engine control module (ECM) input circuit for the torque cut signal
  5. Short to ground in the signal wire between the TCM and ECM
  6. Aftermarket electrical accessories or poor ground connections interfering with the signal circuit
  7. Internal fault in the automatic transmission valve body or solenoids affecting torque signal generation

How to diagnose and fix it

  1. Connect a scan tool and record all stored codes and freeze-frame data to confirm P1698 is the primary fault and not a secondary code
  2. Visually inspect the engine and transmission wiring harness for chafing, corrosion, or loose connectors, especially around the bellhousing and firewall
  3. Measure resistance and voltage on the torque control cut signal wire between the TCM and ECM, checking for a short to ground or an open circuit
  4. Check and clean all ground connections for the ECM and TCM, including the engine block and chassis grounds
  5. If wiring and grounds are good, test the TCM output signal with an oscilloscope or substitute a known-good TCM to rule out an internal driver failure
  6. Inspect the transmission valve body and solenoids for debris or electrical faults if the signal circuit tests normal but the code persists
  7. Clear the code after repairs and perform a road test with the scan tool connected to verify the torque cut signal operates correctly during shifts

What the torque cut signal really does

  • The engine torque control cut signal is a momentary command from the transmission control module to the engine control module to reduce torque during gear changes, so a low input often causes subtle shift quality issues rather than a no-start condition.
  • A common misdiagnosis is replacing the ECM or TCM before checking the wiring harness, because a chafed wire near the transmission bellhousing can short to ground and mimic an internal module failure.
  • Aftermarket remote starters, alarm systems, or poorly installed electrical accessories can backfeed the signal circuit and set P1698 even when the factory wiring is intact.
  • On some Subaru models, a weak or failing battery or alternator can cause voltage drops that trigger this code intermittently, so always verify charging system health before condemning the TCM.
  • P1698 does not always mean the transmission is failing; many cases are resolved by repairing a corroded connector or replacing a shorted section of the signal wire.

Can I keep driving with P1698?

You can usually continue driving with P1698, but avoid aggressive acceleration and towing until the fault is repaired, because compromised torque reduction during shifts can accelerate transmission wear. If the transmission begins shifting harshly or enters limp mode, have the vehicle inspected promptly.

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 Subaru vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage