P0720 Code: Subaru Impreza (2017-2023) - Causes, Symptoms & Fixes

DATA NOTE (data limitations)

• Complaints: No NHTSA owner complaints found for P0720 on 2017-2023 Subaru Impreza in the provided data.
• Recalls: No recalls found in NHTSA database for this make/model/year.
• This guide uses general automotive knowledge for technical explanations and is limited by the absence of complaint/recall data in the supplied source. If you have access to manufacturer service notes or TSBs, treat them as an additional resource.

P0720 DIAGNOSTIC GUIDE FOR 2017-2023 SUBARU IMPREZA

CODE MEANING AND SEVERITY

• Code meaning: P0720 = Output Speed Sensor Circuit Malfunction (often referred to as Output Shaft Speed Sensor circuit). The transmission’s control module (TCM/ECU) uses the output shaft speed signal to monitor gear ratio, torque converter behavior, and shift timing.
• In Subaru Impreza (2017-2023, typically with CVT “Lineartronic” transmissions), the OSS provides the TCM with shaft-speed data essential for proper shifting and torque management.
• Severity: Moderate to high. A true OSS fault can lead to erratic or harsh shifting, incorrect gear selection, or loss of proper throttle response. In some cases the transmission may enter a limp/limp-home mode or exhibit reduced power to protect itself. If the OSS signal is intermittently lost or out of range, repeated shifts or speedometer inaccuracies can occur. If left unresolved, it can place additional load on the transmission and related components.

COMMON CAUSES ON SUBARU IMPREZA

• Faulty Output Speed Sensor (OSS) itself (damaged sensor element, internal short/open circuit).
• Damaged, frayed, or corroded wiring between the OSS and the TCM (insulation wear, pin corrosion, loose connector).
• Faulty or corroded OSS connector(s) or ground/power connections to the transmission/TCM.
• Damaged tone ring/reluctor or sensor mounting issue causing improper signal generation (physical damage or misalignment on the output shaft).
• Transmission control module (TCM) software/calibration issue or a need for software update.
• Low, dirty, or contaminated CVT fluid (level issues or fluid condition can affect sensor operation indirectly and cause fault readings).
• Internal CVT issues that affect the integrity of the speed signal (belt/clutch wear, band/slip conditions) that manifest as irregular sensor readings.
• Other related sensor issues or multiple codes that mask/trigger P0720 (e.g., P0715/P0716 for input speed sensor, P0721/P0722 for other OSS ranges/no signal).

SYMPTOMS (common with P0720 on this platform)

• Rough or erratic transmission shifts (harsh upshifts, delayed shifts, or slipping).
• Inconsistent or incorrect speedometer readings (if OSS feeds the instrument cluster).
• Transmission may enter a “limp mode” or reduced-power state to protect itself.
• Check Engine Light and/or Transmission Warning Light may illuminate.
• Poor acceleration or reduced engine response; higher engine RPM without corresponding speed gain.
• Potential PCM/TCM diagnostic trouble codes related to speed sensors or the transmission.

DIAGNOSTIC STEPS (systematic approach)

Note: Start with the simplest checks and progress to more involved inspections. Document any codes, freeze-frame data, and live data.

A. Confirm and scope the fault

• Use an OBD-II scanner to verify P0720 and note any related codes (P0715, P0716, P0721, P0722, P0723, etc.).
• Check freeze-frame data for RPM, vehicle speed, and fault conditions at the time of the code.
• Confirm there are no widespread electrical faults (battery/ground issues) that could cause sensor abnormal readings.

B. Visual inspection and basic electrical checks

• Inspect OSS wiring harness and connectors at the transmission for obvious damage, wetness, corrosion, or loose connections. Reseat connectors and inspect seals.
• Check for signs of oil leaks around the transmission that could contaminate connectors or wiring.
• Inspect for damaged tone ring/reluctor or misalignment on the transmission output shaft (look for physical damage or movement).

C. Sensor and circuit testing

• With engine off, disconnect the OSS connector and inspect pins for corrosion or bent terminals.
• Perform a resistance/continuity check on the OSS signal wires if you have the service manual’s circuit diagram and proper test procedure. For most OSS sensors, there should be a predictable resistance value and clean signal behavior when tested in-circuit; refer to Subaru-specific wiring diagrams if available.
• With the engine running (where safe), monitor OSS signal using a suitable oscilloscope or a capable scan tool that can display live sensor data or waveform. Look for a clean, regular pulsed signal. An intermittent, absent, or erratic waveform points to sensor, wiring, or connection issues.
• If available, verify that the OSS voltage/reference and ground are stable and within spec; check that the ground path from the OSS to the TCM is solid.

D. Mechanical/relative component checks

• If accessible, inspect the transmission output shaft and its tone ring/reluctor for damage or misalignment. A damaged or dirty tone ring can cause irregular signals even if the sensor itself is fine.
• Consider whether there have been recent transmission repairs or pan drops that might have disturbed the OSS wiring or sensor mounting.

E. Transmission fluid considerations

• Check CVT fluid level and condition. Low or contaminated CVT fluid can lead to various transmission symptoms and sensor anomalies. If fluid is very dirty or at the wrong level, address it per Subaru service guidelines and re-test.
• If fluid service is due or recently performed, verify that the correct CVT fluid specification was used and that any filters or screens were serviced if applicable.

F. Electronic control module/software considerations

• Check for any available software updates or recalibration notices for the TCM/ECU from Subaru. While not a warranty item here, software updates can address sensor interpretation and shift logic in some cases.
• If the vehicle previously had a transmission service or sensor replacement, ensure ECM/TCM re-learn or adaptation procedures were completed as required.

G. Road test and re-check

• After any repair or reseating, clear codes and perform a road test under various loads (light throttle, moderate acceleration, highway speeds) to confirm whether P0720 reappears and whether shifting behavior improves.
• If the fault recurs, perform more advanced diagnostics or consider professional transmission diagnosis (live data logging, scope testing, or pair of diagnostic traces).

H. When to escalate

• If OSS wiring and sensor tests pass but the fault persists, or if the transmission exhibits persistent mechanical symptoms (slipping, clunking, overheating), escalate to a professional with access to Subaru-specific service information and testing tools (e.g., Subaru Select Monitor or equivalent).

RELATED CODES

• P0715: Input/Turbine Speed Sensor Circuit Malfunction
• P0716: Input Speed Sensor Circuit Range/Performance
• P0721: Output Speed Sensor Range/Performance
• P0722: Output Speed Sensor Circuit No Signal
• P0723: Output Speed Sensor Circuit Intermittent
• P0730: Incorrect Gear Ratio (general transmission code; may appear with OSS issues)
• Note: These related codes help triangulate whether the issue is sensor-specific, wiring, or a transmission mechanical problem.

REPAIR OPTIONS AND COSTS (2025 prices, USD)

Prices vary by region, shop, vehicle configuration (CVT vs manual), and labor rates. The ranges below are for guidance and assume typical sedan/hatchback Impreza layouts.

A. Small-scope fixes (DIY-friendly or quick professional service)

• Output Speed Sensor (OSS) replacement (parts only): $15–$120
• OSS connector/wiring harness inspection or simple repair (pin repair, connector cleaning, minor wiring work): $20–$150 (parts typically inexpensive; labor mainly in-shop time if done professionally)
• CVT fluid level/condition check and top-off or simple fluid refresh: $0–$150 (if DIY, only the fluid cost; if performed by a shop, fluid replacement may be $150–$350)

B. Medium-scope fixes (moderate labor)

• OSS replacement with wiring harness inspection (parts + labor): $100–$350
• Sensor wiring repair or connector replacement (labor beyond just parts): $80–$250
• CVT fluid flush/change with Subaru-approved fluid (labor + fluid): $250–$600 (depending on shop and flush method)

C. Moderate-to-large scope (if additional issues are found)

• Transmission fluid change plus filter or screen service (if applicable to CVT): $300–$700
• TCM software update or calibration (dealer or qualified shop): $100–$500
• Tone ring/reluctor inspection or minor transmission body work (if accessible without full teardown): $400–$1,200

D. High-cost repairs (when OSS fault is masking deeper issues or if transmission must be removed/rebuilt)

• Transmission replacement (CVT) or substantial rebuild: $2,500–$6,000+ (labor-heavy; CVT prices vary widely by region and whether you use a remanufactured unit)
• Transmission control module (TCM) replacement or major reprogramming: $1,000–$2,500 (parts + labor)

E. Diagnostic fee

• Many shops charge a diagnostic fee if you don’t proceed with the repair. Typical range: $100–$150 (sometimes waived if you proceed with the repair at the same shop).

Important note: These price ranges are estimates based on typical market conditions in 2025. Your actual costs will depend on your region, shop rates, whether the vehicle is under any warranty, and the exact transmission configuration (CVT vs other), plus the exact nature and extent of the fault found during diagnosis.

DIY VS PROFESSIONAL

• DIY feasibility:
  • Replacing the OSS is commonly doable for a mechanically inclined DIYer with basic hand tools and a solid service manual or guide. Sensor replacement typically requires some access to the transmission pan area or the sensor mount, and may require removal of shields or small fasteners.
  • CVT fluid service and basic electrical checks (connector cleaning, reseating) are reasonable for a DIYer with the right safety precautions.
  • Advanced tests (live data scope, in-depth wiring circuits, or sensor/reluctor tone-ring inspection) are more comfortably done by a professional.
• Professional route:
  • If the OSS test indicates no obvious sensor/connector fault but the fault persists, or if the vehicle shows intermittent symptoms, a certified technician with Subaru-specific diagnostic tools (e.g., Subaru Select Monitor) will be better equipped to perform precise waveform testing, TCM reprogramming, and to rule out mechanical transmission issues without unnecessary component replacement.
  • Transmission work, especially CVT components, often benefits from a professional approach to ensure proper fluid specifications, torque, and adaptation procedures are followed.

PREVENTION

• Use Subaru-approved CVT fluid and avoid mixing fluids. Substituting the wrong fluid can harm the CVT and sensor readings.
• Change CVT fluid at Subaru-recommended intervals (and sooner if severe driving conditions apply). Regular, proper fluid maintenance helps protect sensor readings and the overall transmission health.
• Regularly inspect transmission electrical harnesses and connectors for signs of wear, corrosion, or water intrusion; address any loose or damaged connections promptly.
• Keep the vehicle well-maintained (engine tune-ups, clean fuel system, etc.) to minimize other fault conditions that could interact with the transmission sensors.
• Avoid aggressive driving habits that overly stress the CVT and cause abnormal temperature or belt wear; proper warm-up and gradual throttle application can help prolong sensor health.
• Address any transmission warning lights promptly. Delaying diagnosis can allow minor sensor issues to escalate into more substantial mechanical problems.

SUMMARY

• P0720 on a 2017-2023 Subaru Impreza signals an Output Speed Sensor circuit fault, most often originating from the OSS itself, its harness, or the related connections. In many cases, the fault is sensor- or wiring-related, but it can also be caused by internal CVT/mechanical issues or software considerations.
• There are no recalls or complaints listed in the provided data for this exact code/model/year combination, which means the diagnostic approach should rely on standard electrical and mechanical inspection rather than recall-driven fixes.
• Follow a structured diagnostic path: confirm code, inspect wiring/connectors, test the OSS signal (with appropriate tools), examine tone ring/mounting, check CVT fluid, and consider software updates. If the fault persists after these steps, prepare for a professional diagnosis or potential transmission service.
• Repair costs vary widely depending on the root cause, from a few hundred dollars for sensor/wiring fixes to several thousand dollars for CVT-related repairs or replacement. DIY feasibility exists for sensor/wiring work; more complex CVT issues typically require professional service.