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DTC codes / Subaru codes / P1590

P1590 · SubaruNeutral Position Switch Circuit High Input

P1590 on a Subaru means the engine control module (ECM) is seeing a high-voltage signal on the neutral position switch circuit, which tells the computer whether the manual transmission is in neutral or a gear. The ECM expects a specific voltage pattern as the shifter moves, and a constant high reading indicates an open circuit, a faulty switch, or a wiring problem rather than normal gear selection.

SystemPowertrain
Code typeSubaru specific
SeverityLow
Fix difficultyIntermediate
AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

  • Often no symptoms besides the warning light, especially if the switch fails only intermittently
  • Rough or erratic idle quality when the clutch is depressed in neutral
  • Hesitation or stumble when pulling away from a stop, as the ECM misjudges engine load
  • Incorrect or missing gear indicator information on models with a display
  • Occasional stalling when coasting to a stop with the clutch pedal pressed
  • Poor fuel economy or altered throttle response from incorrect load calculations

Common causes, most likely first

  1. Failed neutral position switch on the manual transmission, worn internally or stuck open
  2. Damaged or disconnected electrical connector at the switch, often from road debris or vibration
  3. Broken, chafed, or corroded wire in the switch circuit between the transmission and ECM
  4. Poor ground connection for the switch circuit, causing a floating high signal
  5. Faulty ECM driver circuit, rare but possible after water intrusion or voltage spikes
  6. Aftermarket clutch or shifter components that alter switch engagement geometry

How to diagnose and fix it

  1. Connect a scan tool and confirm P1590 is active, then read live neutral switch status while moving the shifter through gears
  2. Visually inspect the switch connector and harness at the transmission for corrosion, looseness, or physical damage
  3. Check switch continuity with a multimeter across its terminals in neutral and in gear, comparing to specification
  4. Measure voltage on the signal wire at the ECM connector to rule out an open or shorted harness
  5. Check and clean the switch ground point, then retest the circuit under load
  6. Replace the neutral position switch if it fails the continuity or voltage test, then clear the code and verify
  7. If the circuit tests good but the code returns, inspect the ECM connector and wiring for intermittent faults before condemning the ECM

Neutral switch faults that mimic other problems

  • A high input code often sets because the switch connector has simply come unplugged or the retaining clip has broken, not because the switch itself has failed internally.
  • Technicians sometimes replace the neutral switch only to find the real fault is a chafed wire where the harness passes near the bellhousing or exhaust, so always flex-test the loom.
  • This code can appear alongside misfire or idle codes because the ECM uses neutral switch input for idle stability and load calculations, leading to misdiagnosis of the actual fault.
  • On some Subaru models the neutral position switch shares a ground with other transmission sensors, so a single bad ground can set several codes at once.
  • A scan tool that shows neutral switch status changing correctly while the code remains stored points to an intermittent wiring fault rather than a failed switch.

Can I keep driving with P1590?

You can generally keep driving with P1590 because the fault mainly affects idle quality and load calculations rather than safety systems. Avoid aggressive clutch dumping or towing until repaired, and address the code promptly if you notice stalling or hesitation.

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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