Guide to the 2014-2022 INFINITI QX50 Automatic Transmission Speed Sensor
Experiencing erratic shifting or a check engine light? Your QX50's transmission speed sensor could be the problem.
- For 2014-2017 models, codes P0717 or P0720 may indicate a more serious valve body/TCM failure, not just a sensor fault.
- Confirm your vehicle's generation (2014-2017 vs. 2019-2022) before buying, as transmissions and parts differ.
- Hitachi is a likely OEM supplier, making their aftermarket part a top-tier choice for quality and fit.
- Replacement can be very difficult if the sensor is internal, requiring a professional mechanic.
Understanding Your QX50's Transmission: Two Different Generations
It is critical to know which generation of QX50 you own. The parts are not interchangeable.
- First Generation (2014-2017): These models use a conventional 7-speed automatic transmission. Problems with the speed sensor often lead to noticeable, harsh shifting.
- Second Generation (2019-2022): These models feature a Continuously Variable Transmission (CVT). Sensor issues in the CVT can also cause jerky performance and warning lights.
A Note on P0720 and P0717 Trouble Codes
For the 2014-2017 QX50 with the 7-speed automatic, the trouble codes P0720 (Output Speed Sensor) and P0717 (Input Speed Sensor) are very common. While these codes point to a faulty speed sensor, forum discussions and mechanic videos frequently indicate that the actual root cause is a failure of the Transmission Control Module (TCM), which is integrated into the valve body. Replacing only the sensor may not fix the problem. Many owners report needing to replace the entire valve body assembly, which is a much more expensive and complex repair. There is no active recall for this issue, but it is a widely discussed problem among owners.
Choosing the Right Aftermarket Speed Sensor
When your sensor does fail, you have several good aftermarket options. Since labor can be intensive, choosing a quality part is important.
- Hitachi: Hitachi is a major supplier of original equipment (OEM) parts for many Japanese automakers, including Infiniti. Choosing an aftermarket Hitachi sensor often means you are getting the exact same quality part as the one from the dealer, just in a different box and at a lower price. This is a top-tier choice for reliability.
- Delphi: Delphi is a well-respected global manufacturer of automotive parts. They produce a wide range of sensors that are engineered to meet or exceed OE standards. A Delphi sensor is a solid, reliable replacement part that offers a good balance of quality and cost.
- NGK (NTK): While famous for spark plugs, NGK's sensor division, NTK, produces high-quality transmission speed sensors. They are designed as direct OE replacements and are known for their durability, often featuring heavier wire insulation and robust connectors.
Cost Comparison for Transmission Speed Sensor Replacement
| Part Type | Estimated Cost (Part Only) |
|---|---|
| New OEM (Infiniti) | $482+ |
| New Aftermarket | $94 - $282 |
| Shop Labor | $183 - $269+ |
Pro Tip: Labor costs can vary significantly. For the 2014-2017 models, if the sensor is internal, the transmission pan and sometimes the valve body must be removed, increasing labor time and cost substantially.
Frequently Asked Questions (FAQ)
How many speed sensors does my QX50 transmission have?
Most QX50 models have at least two main transmission speed sensors: an input shaft speed sensor and an output shaft speed sensor. They work together to provide the car's computer with the necessary data for shifting.
Can I replace a transmission speed sensor myself?
It depends on the sensor's location. Some sensors are mounted externally on the transmission case and are relatively easy to access and replace. However, on many 7-speed Infiniti transmissions, the output speed sensor is internal, requiring removal of the drive shaft, transmission pan, and sometimes the valve body. This is a difficult job best left to an experienced mechanic.
What happens if I don't replace a failing sensor?
Ignoring a bad speed sensor can lead to more serious problems. Your vehicle may get stuck in one gear (limp mode), experience severe and damaging shifts, have an inaccurate speedometer, and suffer from poor fuel economy. Continued driving could potentially lead to damage within the transmission itself.
Is an OEM sensor better than aftermarket for my QX50?
Not necessarily. An aftermarket sensor from an OEM supplier like Hitachi can provide the same quality and performance as the dealer part for less money. Reputable brands like Delphi and NGK/NTK also produce high-quality sensors that are reliable alternatives.
Technical Specifications
OEM Part Numbers: 31935-1XF0C 31935-1XF00 31935-X420C
Includes both input (turbine) and output speed sensors. The 2014-2017 models use a 7-speed automatic (RE7R01A), while 2019-2022 models use a CVT. Part compatibility is specific to the transmission type.
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- INFINITI QX50: