2009-2013 INFINITI FX50 Automatic Transmission Speed Sensor Replacement Guide
Experiencing harsh shifting or a P0720 code? Your FX50's transmission speed sensor may be the cause.
- A P0720 code on the FX50 often indicates a failing valve body/TCM, a much more serious issue than just a bad sensor.
- Sensor replacement is a complex job for this vehicle, as it requires removing the driveshaft and opening the transmission housing.
- Hitachi is the likely original equipment manufacturer, making it the highest quality aftermarket choice for this part.
- Always get a professional diagnosis to confirm which sensor has failed and to rule out a bad TCM before purchasing parts.
Symptoms of a Failing Transmission Speed Sensor
When a transmission speed sensor in your FX50 starts to fail, your vehicle will have trouble shifting gears correctly. You might feel sudden, harsh shifts or notice the transmission getting stuck in one gear, a condition often called "limp mode." A check engine light is almost always the first sign of a problem. In some cases, the speedometer may stop working or show an incorrect speed because it relies on data from the output speed sensor.
A Critical Warning for FX50 Owners: The P0720 Code
If your FX50 shows the diagnostic trouble code P0720, use caution. While this code points to the output speed sensor, on the 7-speed automatic transmission used in your vehicle, it is a very common symptom of a much larger problem: a failing Transmission Control Module (TCM). The TCM is attached to the transmission's valve body, and replacing it is a significantly more expensive and complex repair than just changing a sensor. Before buying a new speed sensor, it is highly recommended to have a professional technician diagnose the issue to confirm whether the fault is with the sensor itself or the entire valve body/TCM assembly. This can save you from buying a part you do not need.
Choosing the Right Aftermarket Sensor
When replacing a critical part like a transmission sensor, quality matters. For your FX50, you have a choice between parts that meet original quality standards and those that are a step below.
- Hitachi: Hitachi is a well-known Tier 1 Original Equipment (OE) supplier for Nissan and INFINITI. Choosing a Hitachi sensor often means you are getting the exact same part that was installed in your vehicle at the factory, without the dealership price tag. This is the top-tier choice for reliability and a perfect fit.
- NGK (NTK): NGK is famous for spark plugs, but their sensor division, NTK, is also a respected OE supplier that makes high-quality replacement parts. NTK sensors are designed to meet or exceed original specifications and are an excellent, reliable alternative to the factory part.
Replacement Cost for an FX50 Transmission Speed Sensor
The cost to replace the transmission speed sensor is higher than you might expect because of its location. The output sensor is not easily accessible from the outside. A mechanic must drain the transmission fluid, remove the driveshaft, and take off the transmission's tail housing to reach it. This results in higher labor costs.
| Part/Service | Estimated Cost |
|---|---|
| New OEM Part | $180 - $290 |
| New Aftermarket Part | $95 - $282 |
| Shop Labor | $360 - $600 |
| Total Estimated Cost | $455 - $882 |
Frequently Asked Questions (FAQ)
Where is the transmission speed sensor located on a 2009-2013 FX50?
The most commonly failed sensor, the output speed sensor (related to code P0720), is located inside the rear housing of the transmission. This internal location means it is not a simple part to access, as the driveshaft must be removed first.
Is replacing the transmission speed sensor a DIY job?
No, this is not recommended for beginners. The replacement process involves draining transmission fluid, removing the driveshaft, and disassembling part of the transmission. This requires special tools and a high level of mechanical skill. It is best left to a professional mechanic.
Do I need an input or output sensor?
Your FX50 has both an input and an output speed sensor. The specific trouble code stored in the computer will tell you which one has failed. For example, code P0720 refers to the output speed sensor circuit, while codes like P0725 can be related to the engine or transmission input speed circuit. Always confirm the code before ordering a part.
Are there any recalls for the FX50 transmission speed sensor?
As of early 2026, there are no specific recalls issued by the National Highway Traffic Safety Administration (NHTSA) for the automatic transmission speed sensors on the 2009-2013 INFINITI FX50.
Technical Specifications
OEM Part Numbers: 31935-1XJ0D 31935-1XJ0C 31935-1XJ0A 31935-97X00
Fits the RE7R01A 7-speed automatic transmission. Includes both input (turbine) and output (vehicle) speed sensors, which are sold separately. The output sensor is located in the transmission tail housing.
We Have This Part in Stock
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 FX50: