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DTC codes / Subaru codes / P1700

P1700 · SubaruThrottle Position Sensor Circuit Malfunction AT

P1700 on a Subaru indicates that the transmission control module (TCM) has detected an implausible signal or circuit fault from the throttle position sensor (TPS) circuit that it monitors for shift control. The TCM uses throttle position to calculate shift points and line pressure, so when the signal falls outside expected voltage or rationality limits, it stores this code and may default to a fixed shift strategy.

SystemPowertrain
Code typeSubaru specific
SeverityMedium
Fix difficultyIntermediate
AreaTransmission

Symptoms you may notice

  • Illumination of the check engine light or transmission warning light, often with no other noticeable symptoms
  • Harsh or delayed shifting, especially when accelerating from a stop
  • Transmission stuck in a single gear or failing to downshift during kickdown
  • Poor fuel economy or reduced engine power due to incorrect shift scheduling
  • In rare cases, the vehicle may enter limp mode with limited speed
  • A slight hesitation or stumble on acceleration if the TPS signal is erratic

Common causes, most likely first

  1. Worn or dirty throttle position sensor internal contacts causing an intermittent signal
  2. Damaged or corroded wiring between the TPS and the TCM, including chafed harnesses near the throttle body
  3. Loose or corroded electrical connector at the TPS or TCM
  4. Failed TCM or a software issue in the transmission control module
  5. Throttle body carbon buildup preventing the throttle plate from returning to the correct position
  6. Aftermarket or incorrectly installed electronic throttle control components interfering with the TPS signal

How to diagnose and fix it

  1. Connect a scan tool and read live throttle position data from both the engine control module (ECM) and TCM to compare readings and confirm the fault
  2. Visually inspect the TPS connector and wiring for corrosion, loose pins, or chafing, and repair as needed
  3. Clean the throttle body and perform a throttle relearn procedure if carbon buildup is present
  4. Backprobe the TPS signal wire at the TCM and check for a smooth voltage sweep as the throttle is opened slowly
  5. Test the TPS with a multimeter for dead spots or erratic resistance across its range and replace if faulty
  6. Check for technical service bulletins (TSBs) or software updates for the TCM that address false P1700 setting
  7. After repairs, clear the code and perform a road test with the scan tool to verify the TPS signal remains consistent and the code does not return

Why P1700 is often a wiring issue

  • A common misdiagnosis is replacing the TPS when the real problem is a chafed wire in the harness near the throttle body that only shorts when the engine moves under load.
  • The TCM on many Subaru models shares the throttle position signal with the ECM, so a fault in the shared circuit can set P1700 without any driveability symptoms.
  • Carbon buildup on the throttle plate can cause the TPS voltage to sit just outside the expected range at closed throttle, triggering P1700 without a failed sensor.
  • Aftermarket electronic throttle controllers or piggyback tuners can distort the TPS signal and set this code even though the factory sensor is healthy.
  • A weak battery or poor ground can cause the TCM to misinterpret the TPS signal, so always check charging system and grounds before condemning the sensor.

Can I keep driving with P1700?

You can usually drive the vehicle with P1700, but expect harsh or delayed shifts and reduced fuel economy. Avoid heavy acceleration or towing until the fault is repaired, and if the transmission enters limp mode, seek service 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.

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