P0720 on a 2017 Subaru Outback
Transmission Output Speed Sensor Malfunction
P0720 on a 2017 Subaru Outback indicates transmission output speed sensor malfunction. It usually stays drivable short-term but should be diagnosed promptly. The most common cause is failed output shaft speed sensor element (typically $150–$500). Confirm the root cause before replacing parts.
What does P0720 mean on a 2017 Subaru Outback?
P0720 is set when the transmission control module does not receive a valid signal from the output shaft speed sensor. The TCM uses this signal to compare actual transmission output to expected output for the selected gear and engine RPM — if the signal is missing or implausible, gear ratio calculations fail and the TCM cannot shift correctly. The vehicle typically drops into limp mode (stuck in a default gear, often 3rd or 4th) until the signal is restored.
This guide covers P0720 across the 2015-2019 Subaru Outback generation — the symptoms, causes, and diagnostic steps below apply to every model year from 2015 through 2019.
Is it safe to drive a 2017 Subaru Outback with P0720?
In most cases a 2017 Subaru Outback stays drivable for short trips with P0720 active, but diagnose and repair it promptly. This is a high-severity code — ignoring it can lead to further damage or a failed emissions test.
What are the symptoms of P0720 on a 2017 Subaru Outback?
- Check Engine Light is illuminated
- Speedometer reads zero or fluctuates erratically
- Transmission locked into a single gear (limp mode)
- Hard, harsh, or no shifts
- Cruise control inoperative
- Vehicle may shudder or hesitate at the moment of shift
- Often paired with P0700 (transmission control malfunction)
What causes P0720 on a 2017 Subaru Outback?
| Cause | Likelihood | Estimated repair (USD) |
|---|---|---|
| Failed output shaft speed sensor element | Most common | $150–$500 |
| Damaged sensor connector or harness | Common | $80–$350 |
| Metal debris on the sensor tip (from internal transmission wear) Cleaning the sensor face is a free first attempt. | Common | $100–$400 |
| Damaged tone ring or reluctor wheel inside the transmission | Occasional | $1,500–$4,500 |
| Transmission fluid contamination preventing the sensor from reading | Occasional | $200–$700 |
| Wiring fault between the sensor and the TCM | Occasional | $100–$500 |
| Failed TCM signal input (rare) | Rare | $500–$1,500 |
How to diagnose this on a 2017 Subaru Outback
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Locate the output speed sensor on this transmission
The output shaft speed sensor is typically a two-wire sensor threaded into the rear of the transmission case (RWD vehicles) or the side of the transaxle (FWD vehicles). Some vehicles have it on the transfer case for 4WD. Confirm location in the service manual.
Tools: Vehicle-specific service information
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Check connector and visible wiring
Sensor connectors near the transmission case are exposed to heat, road debris, and sometimes fluid leaks. Unplug and inspect for corrosion, transmission fluid migration up the harness, or visible damage. Clean and re-seat.
Tools: Connector unlock tool, Electrical contact cleaner
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Measure sensor resistance
Most output speed sensors are magnetic or Hall-effect with a typical resistance of 200–1500 Ω. Compare to the service manual. Infinite resistance means an open sensor; near zero means shorted. Either way, replace.
Tools: Multimeter, Service spec sheet
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Verify signal output during rotation
On a lift with the rear wheels free to rotate, spin a rear wheel slowly by hand while watching the output speed PID. The reading should change in proportion to wheel rotation. No response confirms a dead sensor or damaged tone ring.
Tools: Vehicle lift, Scan tool with output speed PID
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Inspect sensor tip for debris
Remove the sensor and look at the magnetic tip. Steel slivers stuck to the magnet are normal — large chunks or clutch material is a warning sign that the transmission is shedding material. Clean the tip and reinstall as a first attempt; consider transmission fluid analysis if heavy debris was present.
Tools: Socket, Magnet pick or wire brush
NHTSA complaints & recalls for the 2017 Subaru Outback
Owner-reported safety complaints and official recalls filed with the U.S. National Highway Traffic Safety Administration for the 2017 Subaru Outback. Use these to gauge how common a problem is on your specific vehicle before you start chasing Subaru Outback diagnostics.
- POWER TRAIN 46
- ENGINE 42
- ELECTRICAL SYSTEM 391
- VISIBILITY/WIPER 205
- UNKNOWN OR OTHER 175
4 active recalls
- AIR BAGS: AIR BAG/RESTRAINT CONTROL MODULE Dec 2019
Subaru of America, Inc. (Subaru) is recalling certain 2016-2017 Outback vehicles. A replacement air bag control module may have been installed that is not compatible with the passenger air bag module, possibly affecting air bag deployment.…
NHTSA campaign 19V910000 - SUSPENSION Aug 2016
Subaru of America, Inc. (Subaru) is recalling certain model year 2017 Outback vehicles manufactured June 20, 2016, to June 23, 2016. The affected vehicles may have improperly tightened attaching bolts for the front left and right brake calipers, wheel hubs, and the right stabili…
NHTSA campaign 16V576000 - STEERING:COLUMN Oct 2016
Subaru of America, Inc. (Subaru) is recalling certain model year 2017 Legacy and Outback vehicles manufactured September 21, 2016, to September 23, 2016. In the affected vehicles, the knee guard bracket may not be properly attached to the steering beam assembly.…
NHTSA campaign 16V716000 - STEERING:COLUMN May 2016
Subaru of America, Inc. (Subaru) is recalling certain model year 2016-2017 Legacy and Outback vehicles manufactured February 29, 2016, to May 6, 2016. The steering column on the affected vehicles may have been improperly machined, and as a result, turning the steering wheel may…
NHTSA campaign 16V292000
How do I fix P0720 on a 2017 Subaru Outback?
- Clean debris off the output speed sensor tip
- Replace the output shaft speed sensor with an OEM part
- Repair sensor connector or harness damage
- Service transmission fluid (drop pan, replace filter and gasket)
- Internal transmission repair if tone ring or shaft damage is confirmed
About the 2015-2019 Subaru Outback
The 2015-2019 Subaru Outback was commonly sold with the following powertrains: 2.5L H4, 2.4L Turbo H4, 3.6L H6. Common trims include Base, Premium, Limited, Touring, Wilderness, Onyx Edition.
Why P0720 puts the transmission into limp mode
The TCM continuously compares output shaft speed to engine RPM and selected gear to verify it is actually getting the gear ratio it commanded. Without a valid output speed signal:
- Ratio verification fails (sets P0731-P0734 in some cases)
- Shift point timing breaks (cannot tell vehicle speed for upshifts)
- Torque converter lockup logic fails (depends on accurate speed)
Limp mode is a protection — the TCM picks a safe default gear and holds it until the signal returns. Drive a short distance to a shop; do not attempt long trips in limp mode.
P0720 with metal on the sensor tip
A small amount of metallic dust on the magnetic sensor tip is normal — it’s the natural wear of bearings and gears over the life of the transmission. Large flakes or clutch material is not normal and indicates internal damage that will eventually cause shifting problems beyond the sensor. If you find heavy debris, do a fluid service and inspect the pan magnet too — together they tell the story of what’s happening inside.
P0720 vs P0500 (Vehicle Speed Sensor)
These can look similar but come from different sources:
- P0500 — vehicle speed signal missing (often the ABS wheel speed sensor on modern vehicles)
- P0720 — transmission output shaft speed signal missing specifically from the transmission’s own sensor
On vehicles where the TCM derives “vehicle speed” from the output shaft sensor, both codes can set together from a single sensor failure.