1990-1993 Chrysler Imperial Automatic Transmission Output Shaft Speed Sensor Guide
If your Imperial's transmission is shifting erratically or the speedometer is dead, the output speed sensor is a likely culprit.
- A faulty output speed sensor is a very common cause of the transmission entering 'limp mode' on a 1990-1993 Imperial.
- Symptoms almost always include a non-working speedometer and a Check Engine Light.
- This is an easy and inexpensive DIY repair that requires basic tools and can be done in under an hour.
- The OEM part number is 4800879; consider replacing the input sensor (4800878) at the same time for peace of mind.
Symptoms of a Failing Output Speed Sensor
The A604 transmission, known as the Ultradrive, was electronically controlled, making it sensitive to sensor failures. When the output speed sensor goes bad on your Imperial, you'll notice serious drivability problems. The most common issue is the transmission going into "limp mode," where it gets stuck in second or third gear to prevent further damage. You may also experience a speedometer that doesn't work at all or shows an incorrect speed. Other signs include harsh, delayed, or erratic shifting between gears and the cruise control not working. A lit Check Engine Light is also a very common symptom.
Limp Mode is a Serious Sign
If your Imperial refuses to shift out of a low gear, it has likely entered limp mode. This is a protective measure by the vehicle's computer. While the car is technically drivable for a short distance, you should get it diagnosed immediately to avoid putting excessive strain on the transmission.
🎬 Watch: A simple fix to try if you're in limp mode.Choosing the Right Aftermarket Sensor
For a vehicle of this age, finding original Mopar parts can be difficult and expensive. Aftermarket sensors are a perfectly acceptable and budget-friendly solution. They are widely available and offer a range of quality and price points. Since this is a critical sensor, choosing a reputable brand is important for long-term reliability.
Brand Quality Tiers
- Premium Aftermarket (e.g., NGK/NTK, Standard Ignition): Brands like NGK (under their NTK electronics line) and Standard Motor Products (SMP) have a strong reputation for producing reliable sensors that meet or exceed OEM specifications. They are often the preferred choice for mechanics who want a part that fits correctly and lasts.
- Standard/Value (e.g., ATP, Dorman): Brands like ATP and Dorman offer a good balance of quality and cost. They are a popular choice for DIY repairs and provide a reliable solution for most owners.
- Economy (e.g., Pioneer Cable, Skyward, True Tech): These brands provide the most budget-friendly options. While they can get your car back on the road, their long-term durability and consistency may not match that of higher-priced brands. Reviews for Pioneer are generally for cable products, but suggest they are functional but not always as robust as OEM.
Pro Tip: The input and output speed sensors on the A604 transmission look very similar and are often sold as a pair. While you may only have a code for the output sensor, it's often a good idea to replace both at the same time, especially given their low cost and the age of the vehicle. The OEM part number for the output sensor is 4800879.
🎬 See a quick overview of the A604 speed sensors.Cost to Replace the Output Speed Sensor
| Item | Estimated Cost |
|---|---|
| New Aftermarket Part | $13.98 - $38.64 |
| Shop Labor | $100 - $170 |
| Total Estimated Cost (DIY) | $13.98 - $38.64 |
| Total Estimated Cost (Shop) | $114 - $209 |
Frequently Asked Questions
Can I replace this sensor myself?
Yes, this is a very DIY-friendly repair. The sensor is located on the outside of the transmission and is typically held in by a single bolt. Access may be tight, but it usually requires only basic hand tools like a socket and ratchet. You will need to safely lift and support the vehicle to gain access from underneath.
What is the difference between the input and output speed sensor?
The A604 transmission uses two main speed sensors. The input sensor measures the speed of the input shaft (from the engine), while the output sensor measures the speed of the output shaft (to the wheels). The computer compares these two signals to verify the transmission is in the correct gear and to detect slippage. A bad output sensor typically affects the speedometer, while a bad input sensor usually does not.
Are there any recalls for this issue?
There are no specific recalls for the transmission speed sensors on the 1990-1993 Chrysler Imperial. There were recalls related to the anti-lock brake system for this vehicle.
Do I need a special tool to replace the sensor?
Typically, no special tools are needed. A 1-inch socket with an extension and a ratchet is usually all that is required to remove and install the sensor. Make sure to disconnect the battery before starting the repair.
Helpful Videos
Technical Specifications
OEM Part Numbers: 4800879 04800879
This sensor is a direct replacement for the output speed sensor on the A604 (41TE) automatic transaxle. It is a threaded sensor with a plastic body and an integrated electrical connector.
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.
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