Infiniti G35 Automatic Transmission Speed Sensor Guide (2003-2008)
Solve harsh shifting and error codes on your G35 by understanding its transmission speed sensors.
- Hitachi is the original equipment manufacturer (OEM) for this part; choosing this brand ensures a correct fit and function.
- Symptoms like harsh shifting can also be caused by a failing TCM or coolant contamination, so a professional diagnosis is crucial.
- Replacement of the output sensor is a complex, labor-intensive job that requires removing the driveshaft.
- Verify whether you need the input (turbine) or output (VSS) sensor, as they are different parts with different locations and error codes.
Understanding Your G35's Transmission Speed Sensors
When dealing with a transmission speed sensor issue on a 2003-2008 G35, it's important to know there are two sensors inside the transmission: the input speed sensor (also called the turbine revolution sensor) and the output speed sensor (often called the Vehicle Speed Sensor or VSS). These are different from the ABS wheel speed sensors located at each wheel. This guide focuses on the sensors inside the automatic transmission.
Common Symptoms of a Failing Speed Sensor
A bad transmission speed sensor sends wrong signals to your car's computer. This can make your G35 act strangely. Look out for these common signs:
- Harsh or Erratic Shifting: The transmission may slam into gear, or shift at the wrong times.
- Stuck in Gear: The transmission might go into a "limp mode" to protect itself, often getting stuck in a single gear.
- Check Engine Light: A failed sensor will almost always trigger a Check Engine Light. Common codes include P0720 (Output Speed Sensor) and P0725 (Input Speed Circuit).
- Faulty Speedometer: The speedometer may stop working, jump around, or show the wrong speed.
- Cruise Control Not Working: The cruise control system relies on accurate speed data, so it will shut off if the sensor is bad.
Warning: It Might Not Be the Sensor
The RE5R05A transmission in the G35 has other known issues that can mimic a bad speed sensor. Before buying parts, be aware of two common problems: TCM/Valve Body Failure and Coolant Contamination. A leak in the radiator can allow coolant to mix with transmission fluid, destroying the internal electronics. A professional diagnosis is highly recommended to avoid a costly misdiagnosis.
Choosing the Right Aftermarket Part: Brand Tiers
For a critical part like this, quality matters. You don't want to perform a difficult repair twice.
- Tier 1 (OEM Supplier): Hitachi
Hitachi is the Original Equipment Manufacturer (OEM) for many of Nissan and Infiniti's electronic parts, including these sensors. Choosing a Hitachi sensor gives you the exact same part that the factory installed, ensuring perfect fit and performance without the dealership price tag. - Tier 1 (Premium Aftermarket): NGK/NTK
NGK, which sells sensors under the NTK brand, is a top-tier manufacturer known for quality. While not the original supplier for this specific part, their products are engineered to meet or exceed OEM standards and are a reliable alternative if Hitachi is unavailable.
Transmission Speed Sensor Replacement Cost
Replacing the output speed sensor on the G35 is a labor-intensive job. The sensor is located inside the transmission's tail housing, which requires removing the driveshaft to access. This is not a simple unbolt-and-replace task. The input sensor is also located on the valve body, requiring removal of the transmission pan.
| Part Type | Estimated Cost |
|---|---|
| New OEM | $250 - $400 |
| New Aftermarket (Hitachi, NGK) | $94.78 - $281.91 |
| Shop Labor | $500 - $900 |
Cost estimates are approximate and can vary by location and vehicle condition.
Frequently Asked Questions
Is this a DIY job for a home mechanic?
This is not recommended for beginners. Replacing the output speed sensor requires removing the driveshaft, transmission mount, and tailshaft housing. It's a complex job that requires significant tools and experience. The input sensor is slightly easier but still involves draining fluid and dropping the transmission pan and valve body.
What is the difference between the input and output sensor?
The input sensor tells the computer how fast the engine is turning the transmission's input shaft. The output sensor tells the computer how fast the transmission is sending power to the wheels. The computer needs both signals to shift correctly. They are different parts and are not interchangeable.
My car has a P0720 code. Is it definitely the output speed sensor?
A P0720 code points to a problem in the output speed sensor circuit. While a faulty sensor is the most common cause, the problem could also be old or low transmission fluid, a wiring issue, or a failing Transmission Control Module (TCM). Always check the fluid level and condition first.
Should I replace both sensors at the same time?
Given the high labor cost and difficulty of accessing these sensors, it is wise to consider replacing both if you have the transmission opened up, especially on a higher-mileage vehicle. This can prevent having to pay for the same labor twice if the second sensor fails later.
Helpful Videos
Technical Specifications
OEM Part Numbers: 31935-1XJ0A 31935-1XJ0D 31935-AL50A
Fits the RE5R05A 5-speed automatic transmission. Includes both an input (turbine) and output (vehicle speed) sensor, which are sold separately.
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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 G35: