Ford Aerostar 1986-1997 Vehicle Speed Sensor: A Complete Guide
Solve your Aerostar's erratic speedometer and rough shifting by understanding its speed sensor.
- The VSS is also the rear ABS sensor, located on the rear differential on most 1990-1997 Aerostars.
- Symptoms are nearly identical to a failed PSOM (instrument cluster module), a common point of failure.
- A bad sensor will cause an erratic speedometer, hard shifting, and a flashing O/D light.
- Replacement is easy for DIYers and requires only basic tools.
Is Your Aerostar's Speed Sensor Failing?
A bad vehicle speed sensor can cause several noticeable problems. Because the sensor is located on the rear differential, it lives in a harsh environment of heat and dirt, which can cause it to fail over time. The wiring leading to the sensor can also get damaged.
Common Symptoms of a Bad VSS:
- Erratic or Dead Speedometer: The needle may bounce around, read incorrectly, or not move at all.
- Harsh Transmission Shifting: The transmission may shift hard, late, or seem to hunt for the right gear.
- Flashing Overdrive (O/D) Light: A blinking "O/D OFF" light on the shifter is a common sign of a speed signal problem.
- Cruise Control Not Working: The cruise control system needs to know the vehicle's speed to function. If it can't get a reliable signal, it won't engage.
- ABS Light On: Since the VSS often doubles as the rear ABS sensor, a failure can trigger the ABS warning light on your dashboard.
A Word of Warning: VSS vs. PSOM
On these Ford Aerostars, the symptoms of a bad VSS are identical to a failure of the Programmable Speedometer/Odometer Module (PSOM). The PSOM is a circuit board inside your instrument cluster that processes the signal from the VSS. It's a known issue for the PSOM to fail, causing the exact same speedometer and shifting problems. Before buying a new sensor, it's wise to check for bad wiring or consider that the PSOM might be the real problem, which is a more involved repair.
Choosing the Right Aftermarket Speed Sensor
When shopping for a new VSS, you have several options. The quality can vary, so it's important to know the difference.
- OEM (Motorcraft): Motorcraft is Ford's own brand. It's the original part your Aerostar was built with and is considered the highest quality and most reliable choice. If you want a guaranteed fit and long life, this is your best bet.
- Premium Aftermarket (Delphi, Standard Ignition): Brands like Delphi and Standard Motor Products (Standard Ignition) have a strong reputation for making quality parts that meet or exceed OEM standards. They are an excellent alternative to the dealer part, often at a better price.
- Standard Aftermarket (Dorman, Holstein): Dorman is a very common brand that makes a huge variety of parts. Their quality can sometimes be a mixed bag; some parts are great, while others may not last as long as premium brands. Holstein is another option in this tier. These brands offer a good balance of price and availability.
- Economy Aftermarket (Walker Products, True Tech): These brands focus on being the most affordable option. They can be a good choice for a budget repair, but may not have the same long-term durability as more expensive brands.
How Much Does a Ford Aerostar VSS Cost?
The cost depends on the brand you choose and whether you do the work yourself. The job is simple enough for many DIY mechanics.
| Part Type | Estimated Part Cost | Estimated Shop Labor Cost |
|---|---|---|
| New OEM (Motorcraft) | $75 - $150 | $85 - $125 |
| New Aftermarket | $32 - $270 | |
| Used OEM | $20 - $50 |
Frequently Asked Questions
Where is the Vehicle Speed Sensor located on a Ford Aerostar?
For most 1990-1997 models (especially those with rear ABS), the Vehicle Speed Sensor is located on the top of the rear differential housing. It is held in place by a single bolt. On some very early or 2WD models without rear ABS, a sensor may be located on the transmission tail shaft.
Can I replace the VSS myself?
Yes, this is a very DIY-friendly job for most people. The sensor is easy to access on the rear axle. The process involves disconnecting the electrical plug, removing one bolt, and carefully pulling the old sensor out. You should clean the mounting surface before installing the new sensor with a fresh, lubricated O-ring.
What happens if I don't replace a bad VSS?
Driving with a bad VSS can be unsafe and cause more damage. Your speedometer will be unreliable, and you risk getting a speeding ticket. More importantly, the constant hard shifting can cause premature wear and tear on your automatic transmission, leading to a much more expensive repair down the road.
Is there a recall on the Aerostar speed sensor?
No, there are no active recalls from the NHTSA for the Vehicle Speed Sensor on the 1986-1997 Ford Aerostar. There was a Technical Service Bulletin (TSB 96-21-11) issued for speedometer wavering that mentioned the VSS and the PSOM as potential causes.
Technical Specifications
OEM Part Numbers: F85Z9E731AB F85Z2L373AC F3TZ2L373A ZZL043711
Typically a 2-pin magnetic sensor that mounts on the rear differential housing. It functions as both the Vehicle Speed Sensor and the Rear ABS 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.
- Ford Aerostar: