Lexus LS400 (1990-2000) Automatic Transmission Input Shaft Speed Sensor Guide
Address erratic shifting and Check Engine warnings by understanding this critical transmission sensor in your LS400.
- A faulty input speed sensor is a common cause of shifting problems and a P0715 code on the LS400.
- Replacement is a simple, low-cost DIY job for most owners.
- A quality aftermarket brand like Standard Ignition is a cost-effective alternative to an expensive OEM part for this repair.
- Confirm your vehicle year, as 1998-2000 models have a different transmission and speed sensing system than earlier models.
Is Your LS400 Transmission Acting Up? It Could Be the Input Speed Sensor.
If your Lexus LS400 is experiencing sudden shifting problems, a Check Engine Light, or seems to get stuck in gear, a faulty Automatic Transmission Input Shaft Speed Sensor is a likely culprit. This sensor is a critical part of what makes the electronically controlled transmission in your Lexus shift so smoothly. When it fails, it can cause a range of frustrating and concerning symptoms. This guide will walk you through the signs of failure, what to look for in a replacement, and what you can expect for repair costs.
Important Note for 1998-2000 LS400 Owners
The 1998-2000 LS400 uses a 5-speed automatic transmission (the A650E), which is different from the 4-speed (A341E) in earlier 1990-1997 models. While many symptoms overlap, the speed signal for the speedometer on these later models primarily comes from the ABS wheel speed sensors. A fault code like P0715 still points toward the transmission's input/turbine sensor, but other codes could be related to the ABS system. Always confirm the specific part and issue for your vehicle year.
Symptoms of a Failing Input Shaft Speed Sensor
A bad input speed sensor sends incorrect or no information to the car's computer, leading to several noticeable problems:
- Harsh or Erratic Shifting: The transmission may slam into gear, shift at the wrong times, or feel jerky between shifts.
- Transmission Stuck in Gear (Limp Mode): The computer may put the transmission into a single gear (often 2nd or 3rd) to prevent further damage.
- Check Engine Light: A fault in the sensor's circuit will trigger a Check Engine Light. The most common trouble code is P0715 (Input/Turbine Speed Sensor "A" Circuit).
- Flashing "O/D OFF" Light: On older models, a flashing overdrive light is a common indicator of a transmission sensor fault.
- Failure of Cruise Control: The cruise control system relies on accurate speed data and will often stop working if the sensor fails.
Choosing the Right Aftermarket Part: OEM vs. Aftermarket
For a vehicle like the 1990-2000 LS400, you have a choice between an original equipment manufacturer (OEM) part from Lexus/Toyota and an aftermarket part. For a simple electronic sensor like this, a quality aftermarket brand can offer significant savings without a major compromise in quality.
- OEM: Made by the original manufacturer (like Aisin or Denso for Toyota/Lexus), these parts are guaranteed to fit and function perfectly but come at a higher cost.
- Aftermarket (Standard Ignition): Brands like Standard Motor Products (Standard Ignition) are well-established in the aftermarket and produce reliable replacement parts that meet or exceed OEM specifications. For a sensor that is relatively easy to replace, the cost savings of an aftermarket part make it a very practical choice for most owners.
Pro Tip: The LS400 transmission often has two main speed sensors (input and output). They look very similar and are located near each other on the transmission case. Sometimes, simply cleaning the magnetic tip of the sensor from metallic fuzz can resolve the issue. If you are replacing one, it's good practice to inspect the other for wear or damage.
Replacement Cost
Replacing the input shaft speed sensor is a relatively inexpensive repair. The part itself is affordable, and labor is minimal because the sensor is externally mounted on the transmission case.
| Part/Service | Estimated Cost |
|---|---|
| New Aftermarket Sensor (Standard Ignition) | $45 - $70 |
| Shop Labor | $75 - $150 |
| Total Estimated Cost | $120 - $220 |
Frequently Asked Questions (FAQ)
Where is the input speed sensor located on the LS400?
The input speed sensor (and the output sensor) is located on the driver's side of the transmission housing. It is held in by a single bolt (often 12mm) and has an electrical connector. You may need to remove the airbox for easier access on some models.
Can I replace this sensor myself?
Yes, this is a very DIY-friendly job. It typically involves safely raising the vehicle, locating the sensor on the transmission, disconnecting the electrical plug, removing one bolt, and swapping the old sensor for the new one. The entire process can usually be done in under an hour with basic hand tools.
What happens if I don't replace a bad sensor?
Continuing to drive with a bad input speed sensor can cause long-term damage to your transmission. The constant hard shifting and incorrect pressures can wear out clutches and other internal components, leading to a much more expensive repair down the road. It is recommended to address the issue promptly.
Is the input speed sensor the same as the output speed sensor?
No, they serve different functions, but they often look identical and are located near each other. The input sensor measures the speed of the shaft coming from the engine/torque converter, while the output sensor measures the speed of the shaft going to the driveshaft (vehicle speed). On some LS400 models, the two sensors are interchangeable parts. However, it's crucial to diagnose which one has failed before replacing it.
Technical Specifications
OEM Part Numbers: 89413-50010 89413-24010
2-Terminal Magnetic Sensor
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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.
- Lexus LS400:
- 🛍️ Shop This Part
- Is Your LS400 Transmission Acting Up? It Could Be the Input Speed Sensor.
- Important Note for 1998-2000 LS400 Owners
- Symptoms of a Failing Input Shaft Speed Sensor
- Choosing the Right Aftermarket Part: OEM vs. Aftermarket
- Replacement Cost
- Frequently Asked Questions (FAQ)
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