A P0717 code in your 2021 Subaru Outback indicates a complete loss of signal from the input/turbine speed sensor. Unlike codes for out-of-range readings, P0717 means the TCM is receiving no signal at all from this sensor. Your Outback uses a continuously variable transmission (CVT) that relies heavily on accurate speed data.
No Signal Implications
Without input speed data, your Outback's CVT cannot properly calculate pulley ratios, detect slippage, or control the steel belt operation safely. The TCM will likely enter a failsafe mode that severely limits transmission functionality to prevent damage. This is a critical code that prevents normal operation.
Common Causes
A completely failed input speed sensor is the obvious cause. Open circuit wiring between the sensor and TCM prevents signal transmission. A disconnected or corroded connector breaks the signal path. The sensor's reluctor ring may have failed or become misaligned. In rare cases, the TCM's input circuit for this sensor has failed.
Symptoms in Your Outback
The CVT enters failsafe or limp mode almost immediately. The transmission may lock into a single ratio or refuse to move at all. Warning lights illuminate for the transmission and check engine. You may feel the CVT operating abnormally—no ratio changes or harsh engagement. Vehicle may be barely drivable or undrivable depending on failsafe severity.
Diagnostic Steps
Using Subaru SSM, verify there is truly no signal by monitoring input speed data—it should show zero or no reading at all. Check for voltage at the sensor connector with the key on. Test sensor resistance against specifications. Verify wiring continuity from sensor to TCM. Inspect the sensor and reluctor ring for physical damage. If all checks out, suspect TCM input circuit failure.