INFINITI FX35 (2003-2012) Transmission Speed Sensor: A Complete Guide
Solve erratic shifting and check engine lights by understanding your FX35's transmission speed sensors.
- Verify your transmission type: 2003-2008 models generally have a 5-speed, while 2009-2012 have a 7-speed, which affects sensor location.
- A trouble code like P0717 or P0720 points to a speed sensor, but always check the wiring and connector for damage first.
- Hitachi is the Original Equipment supplier for this part, offering OEM quality at a better price than the dealer.
- Before ordering, confirm if your failed sensor is external or internal to the transmission, as only external sensors are simple DIY replacements.
Is Your FX35 Shifting Strangely? It Could Be a Transmission Speed Sensor
If your INFINITI FX35 is experiencing harsh shifting, getting stuck in gear, or has the 'Service Engine Soon' light on, a failing automatic transmission speed sensor is a likely culprit. These sensors are critical electronic components that tell your vehicle's computer when to shift. While a sensor failure can feel like a major transmission problem, the fix is often straightforward and affordable, especially if your vehicle uses externally mounted sensors.
Important: 5-Speed vs. 7-Speed Transmissions
The 2003-2012 FX35 was equipped with two different automatic transmissions. It's crucial to know which one your vehicle has before ordering parts.
- 2003-2008 FX35: These models typically use the 5-speed RE5R05A transmission. On many of these vehicles, both the input and output speed sensors are mounted externally and can be replaced individually. 🎬 See this walkthrough for replacing an external speed sensor
- 2009-2012 FX35: These models use a newer 7-speed RE7R01A transmission. On these units, the input speed sensor is often integrated into the Transmission Control Module (TCM) inside the transmission oil pan. This internal sensor cannot be replaced as a separate part; the entire valve body/TCM assembly must be replaced, which is a much more complex and expensive job. Aftermarket sensors are typically for the external output sensor on these models.
Common Symptoms of a Failing Speed Sensor
When a transmission speed sensor fails, the TCM loses critical data. This can cause a variety of symptoms as the system tries to protect itself from damage.
- Harsh or Erratic Shifting: The most common sign is rough, jerky, or delayed gear changes. The transmission may feel like it's slamming into gear. 🎬 Watch: See how erratic shifting looks and feels in an FX35
- Stuck in Gear (Limp Mode): The transmission may lock itself into a single gear (often 3rd or 4th) to prevent further damage, severely limiting your speed.
- Check Engine Light: A failing sensor will almost always trigger a 'Service Engine Soon' light. Common trouble codes include P0717 (Input Speed Sensor Circuit) and P0720 (Output Speed Sensor Circuit).
- Malfunctioning Speedometer or Cruise Control: Since the output sensor measures vehicle speed, its failure can cause the speedometer to stop working or behave erratically, which will also disable the cruise control.
Choosing the Right Aftermarket Speed Sensor
For electronic parts like transmission sensors, quality is critical. A cheap, poorly made sensor can fail quickly or provide inaccurate readings, leading to the same problems you were trying to fix. For the FX35, two reputable aftermarket brands are available.
Brand Tiers for INFINITI FX35
Tier 1 (OE Equivalent): Hitachi
Hitachi is a Tier 1 Original Equipment (OE) supplier for Nissan and INFINITI, meaning they likely manufactured the original sensor that came in your FX35 from the factory. Choosing a Hitachi sensor gives you OEM quality and performance without the dealership price tag. For this part, Hitachi is the recommended choice for reliability and value.Tier 2 (Premium Aftermarket): NGK/NTK
NGK, which sells sensors under the NTK brand, is a world-renowned company famous for its quality ignition parts and sensors. NTK sensors are built to meet or exceed OE specifications and undergo extensive testing. While they are an excellent quality part, they often come at a significantly higher price than Hitachi for this specific application.
Pro Tip: Before replacing a sensor, inspect the wiring harness and connector carefully. A corroded pin or damaged wire can cause the exact same symptoms as a failed sensor and is a much cheaper fix.
Cost of Replacing an FX35 Transmission Speed Sensor
The cost can vary significantly depending on whether your sensor is external or internal. The prices below reflect the replacement of a single, externally mounted sensor.
| Part/Service | Estimated Cost |
|---|---|
| New OEM Sensor | $180 - $300 |
| New Aftermarket Sensor (Hitachi, NGK) | $94 - $282 |
| Shop Labor (External Sensor) | $120 - $250 |
| Total Professional Replacement | $214 - $532 |
Frequently Asked Questions
Can I drive my FX35 with a bad transmission speed sensor?
It is not recommended. While the vehicle may be drivable in 'limp mode,' you will have unpredictable shifting, poor acceleration, and potentially no speedometer. This can be unsafe in traffic. Continued driving could also put extra strain on other transmission components.
Are there two different speed sensors I might need to replace?
Yes. The transmission uses both an input and an output speed sensor. A diagnostic scan tool is needed to read the specific trouble code (e.g., P0717 for input, P0720 for output) to determine which sensor has failed. Sometimes, mechanics recommend replacing both at the same time, especially on higher-mileage vehicles.
Is the speed sensor located inside the transmission?
It depends on your FX35's model year. On most 2003-2008 models with the 5-speed automatic, the sensors are on the outside of the transmission case and are easy to access. On 2009-2012 models with the 7-speed, the input sensor is often internal, but the output sensor is typically still external. 🎬 Watch: How to fix the P0720 code on 7-speed transmissions Always verify the location on your specific vehicle before starting the repair.
Is there a recall for the transmission speed sensor on the FX35?
No, there are no active recalls from INFINITI or NHTSA specifically for the transmission speed sensors on the 2003-2012 INFINITI FX35. Some Technical Service Bulletins (TSBs) exist for shifting issues on later models, but these usually involve reprogramming the computer, not replacing the sensor itself.
Helpful Videos
![P0720 [ Nissan/Infiniti 7at Automatic Transmission Fix ]](https://img.youtube.com/vi/Hmfrc9_6BME/mqdefault.jpg)
Technical Specifications
OEM Part Numbers: 31935-1XJ0D 31935-1XJ0C 31935-1XJ0A 31935-97X00
The automatic transmission contains an input speed sensor and an output speed sensor. The sensors are typically magnetic reluctance-type sensors that generate a signal as a toothed wheel on the transmission shaft rotates past them. The frequency of this signal is proportional to the shaft's speed.
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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 FX35: