P0720 Ford F150 – Troubleshooting Output Speed Sensor Failures
The P0720 code indicates an issue with the Output Speed Sensor (OSS) circuit in your transmission, which often results in erratic shifting or a non-functioning speedometer. This guide helps you diagnose whether the problem is a faulty sensor, a wiring harness issue, or a deeper internal transmission fault.
You are cruising down the highway in your F150, and suddenly, the check engine light flickers to life. Your transmission starts acting lazy, or perhaps your speedometer needle decides to stop reporting your speed entirely.
It is frustrating, but you are not alone. Many F150 owners encounter the p0720 ford f150 diagnostic trouble code when their vehicle’s computer stops receiving accurate data from the transmission’s output shaft.
In this guide, we will break down exactly what this code means for your truck. We will walk through the steps to diagnose the issue, determine if you can fix it in your driveway, and get you back on the road safely.
Understanding the p0720 ford f150 Error Code
The P0720 code stands for Output Speed Sensor Circuit Malfunction. In your Ford F150, the Transmission Control Module (TCM) uses this sensor to track how fast the output shaft is spinning.
This data is critical for the vehicle’s computer to decide when to shift gears. When the signal is lost or corrupted, the transmission defaults to “limp mode” to protect itself from internal damage.
If you see this code, do not panic. It is often a simple electrical issue rather than a catastrophic mechanical failure. However, ignoring it can lead to poor fuel economy and potentially unsafe driving conditions.
Common Symptoms of an OSS Failure
When the p0720 ford f150 error appears, your truck will likely tell you something is wrong before you even hook up a scanner. Pay close attention to how the vehicle behaves under load.
- Erratic Shifting: The truck may struggle to find the right gear or shift harder than usual.
- Inoperative Speedometer: If the computer doesn’t know how fast the output shaft is spinning, it often cannot calculate your vehicle speed.
- Limp Mode: The transmission may lock into a single gear, usually second or third, to prevent further damage.
- Check Engine Light: This is your primary notification that the onboard diagnostics have flagged a sensor discrepancy.
Step-by-Step Diagnostic Process
Before you start replacing parts, you need to verify the source of the trouble. A multimeter and a basic OBDII scanner are your best friends during this process.
Checking the Wiring and Connections
Start by inspecting the wiring harness leading to the Output Speed Sensor. In many F150 models, road debris, heat, or vibration can cause the wires to chafe or snap near the transmission housing.
Check the connector for corrosion or loose pins. Use a contact cleaner if you see any signs of moisture or oxidation inside the plug. A solid connection is vital for the low-voltage signals the sensor sends to the computer.
Testing the Sensor Resistance
If the wiring looks good, use your multimeter to check the resistance of the sensor itself. Disconnect the sensor and measure the resistance across the two pins.
Compare your reading to the specifications in your factory service manual. If the reading is infinite (open circuit) or zero, the internal coil of the sensor has likely failed and requires replacement.
Replacing the Output Speed Sensor
Replacing the OSS is a manageable job for most DIYers. You will need a standard socket set, a drain pan, and a new sensor from a reputable manufacturer.
- Secure the Vehicle: Always use jack stands if you are lifting the truck. Never rely solely on a floor jack.
- Locate the Sensor: It is typically found on the tail shaft housing of the transmission, near the drive shaft.
- Prepare for Fluid Loss: Have a drain pan ready, as a small amount of transmission fluid will leak out when you pull the sensor.
- Remove and Install: Unbolt the retaining screw, pull the old sensor out, and install the new one with a fresh O-ring to prevent leaks.
After installing the new part, top off your transmission fluid to the correct level. Always check the fluid level while the engine is at operating temperature to ensure accuracy.
When to Seek Professional Help
Sometimes, the p0720 ford f150 code persists even after you replace the sensor and inspect the wiring. This could indicate a deeper problem within the transmission, such as a damaged tone ring or a faulty TCM.
If you have cleared the codes and the issue returns immediately, you might be dealing with an internal mechanical failure. At this point, it is wise to visit a transmission specialist who has access to advanced diagnostic software.
Professional shops can perform a “pinpoint test” on the wiring harness between the sensor and the computer. This ensures there isn’t a hidden break in the wire inside the frame rail.
Frequently Asked Questions About p0720 ford f150
Can I drive my truck with a P0720 code?
While you can drive short distances, it is not recommended. Driving in limp mode puts extra stress on the transmission and can lead to overheating or permanent mechanical damage.
Is the OSS the same as the Vehicle Speed Sensor (VSS)?
On many newer F150s, the transmission uses the output speed sensor data to calculate vehicle speed. While they serve similar purposes, they are distinct components depending on your specific year and transmission model.
Do I need to reset the computer after the repair?
It is best practice to clear the code with your OBDII scanner after the repair. This allows the computer to start fresh and helps you confirm immediately if the fix was successful.
How much does a new sensor cost?
The sensor itself is relatively inexpensive, usually ranging from $30 to $80 depending on the brand. Choosing an OEM or high-quality aftermarket part is always a smart investment for your truck’s reliability.
Final Takeaways for the F150 Owner
Tackling a p0720 ford f150 issue is a great way to learn more about your truck’s drivetrain. By focusing on the wiring and the sensor first, you can often save hundreds of dollars in repair bills.
Always prioritize safety by using proper lifting equipment and wearing protective eyewear when working under the vehicle. If you take your time and follow the diagnostic steps, you will have your F150 shifting smoothly again in no time.
Stay patient, keep your tools organized, and don’t hesitate to reach out to a professional if you feel out of your depth. Happy wrenching, and stay safe on the road!
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