What It Is And How To Fix It

Your speedometer is more important than you may realize. The Powertrain Control Module (PCM) uses information from it to control many functions such as cruise control, idle speed, transmission operation, Exhaust Gas Recirculation (EGR) valve operation, Anti-Lock Brake System (ABS) operation, and traction control, to name a few. Where speed is concerned, the Output Shaft Speed (OSS) sensor is critical for communicating with the PCM to, for example, dictate when the transmission shifts gears. If the OSS sensor fails, the P0720 fault code will be stored by your vehicle. This is an issue you should fix quickly, so let’s look at how to go about doing that.

What Does The P0720 Error Code Mean?

Today’s vehicles use many sensors, including speed sensors. Speed sensors are critical in dictating what the PCM does and when it chooses to do it. The P0720 error code specifies that the OSS sensor, otherwise known as a Vehicle Speed Sensor (VSS), is malfunctioning. This speed sensor provides information to the PCM that affects many system operations. If your vehicle has set the P0720 error code, the PCM has indicated the information received by the OSS sensor signal is not as expected or desired. The P0720 code is generic, so whether you have a Ford, Honda, Mercedes-Benz, or almost any other model, this code could be triggered on your vehicle.

Gear-driven output shaft speed sensor (above)

What Causes The P0720 Error Code?

There are a few possible causes that will lead to the P0720 error code, such as:

• Defective, worn, or dirty OSS sensor
• Corroded or damaged output speed sensor circuit
• Faulty PCM
• Contaminated transmission fluid
• Damaged transmission internals

Symptoms Of The P0720 Error Code

Depending on your vehicle’s make and model, the symptoms you can experience with the P0720 error code vary. The following are reported symptoms:

• Improper or harsh gearshifts
• Stalling when coming to a stop
• Rough or low idle speed
• Improper ABS or traction control operation
• Inoperative or malfunctioning speedometer
• Inoperative or malfunctioning odometer

Can I Drive My Car With This Issue?

Some vehicles will be badly affected by the active P0720 error code, whereas others will not. Whether or not you can continue driving your vehicle will depend on the symptoms it exhibits. A vehicle can enter “fail-safe” or “limp” mode with the error code present, which means you won’t be able to drive it with full power. The P0720 error code will affect transmission and engine operation, while power delivery and fuel economy can be reduced. In light of these issues, this is a fault code that demands quick attention.

How To Fix A P0720 Error Code On Your Vehicle

There are several ways to fix the P0720 error code. Depending on the specifics of your fault, one of these repairs may remedy the P0720 code affecting your vehicle.

Before attempting any repairs, you should verify that the P0720 error code is active on your vehicle. Your vehicle’s PCM can be scanned by most local parts stores for free or by a service facility, sometimes for a fee. Once the P0720 code has been verified, you can begin with a few simple checks.

Transmission Fluid

Your vehicle’s transmission fluid level and condition are vital to its operation. If your vehicle is experiencing harsh or improperly timed shifts, you’ll want to inspect the transmission fluid.

We strongly advise consulting your service manual before attempting to inspect or change your transmission fluid. Not all transmissions use dipsticks to check their fluid level. Some transmissions need to be within a specific temperature range with the inspection plug removed. If this applies to your vehicle, it’s best to let the professionals handle this service.

To check your transmission fluid, follow these steps:

1. Position your vehicle on flat level ground, and run the engine with the vehicle in Park
2. Remove the dipstick (if there is one) and inspect the fluid level, color, and odor

If the fluid is heavily discolored or smells burnt, there’s a good chance your transmission has worn internals and may need to be replaced or rebuilt. If your fluid is light brown and only has a minor burnt odor, you can service the transmission.

Overfilled or underfilled transmissions are never good. Ensure your transmission fluid is at the correct level, but consult a professional if you aren’t certain about how much fluid is required.

Speed Sensor Inspection

Another way to resolve the P0702 code starts by identifying the location of the output speed sensor, which varies by vehicle configuration. On vehicles with longitudinally mounted engines – typically those with rear-wheel drive, such as a Ford F-150 or Jeep Grand Cherokee – the speed sensor is often located towards the tail housing of the transmission. On vehicles commonly using transversely mounted engines – typically those with front-wheel drive like a Hyundai Elantra – the output speed sensor will most likely be located on the front of the transmission.

• Inspect the speed sensor wire harness for any damage or corrosion. If corrosion is found, use an electrical contact cleaner and remove it. In some cases, the corrosion can penetrate the wiring and replacement of the wire harness may be needed. Stabilant 22A is a contact enhancer that helps maintain a good electrical connection, even if there’s corrosion.
• Measure the sensor’s resistance using an ohmmeter. Typical 2-wire speed sensors have a resistance specification of 560 to 680 Ohms. Always consult your service manual for the correct testing specifications. If a sensor measures outside the desired range, replace the sensor.
• Remove, inspect, and clean the sensor if required. Speed sensors can become covered in fine metals, preventing them from reading accurately. Remove the speed sensor for inspection; if the sensor appears to be dirty, try cleaning it. If the sensor appears to have physical damage, replace it. Additionally, some speed sensors will have a plastic gear that’s driven by the transmission output shaft. These plastic gears can wear or even break. While the sensor is removed, check the transmission output shaft gear with a flashlight. Severely worn or damaged output shafts can cause the speed sensor signal to become weak or disrupted. If the output shaft is damaged, a transmission rebuild or replacement may be necessary.

How Much Does It Cost To Fix?

The cost to repair a P0720 error code will vary depending on the vehicle’s specific failure, make, and model. In most cases, the error code can be remedied by replacing the output shaft speed sensor or by servicing the transmission fluid. RepairPal estimates replacing an output shaft speed sensor costs between $290 and $340, on average. The cost of replacing transmission fluid comes in at around $200. However, this service varies dramatically due to the specific fluid your transmission uses.

Transmission rebuilds and replacements are far more expensive, which is why proper periodic transmission fluid maintenance is necessary. Most basic powertrain warranties are five years/60,000 miles, with extended warranties covering up to 10 years/120,000 miles.

A transmission replacement will range from $2,000 to $6,000 if your vehicle isn’t covered under warranty. This depends on whether a used, rebuilt, or new unit is installed. So, we recommend checking for service campaigns, recalls, and warranty enhancement programs that may lead to your vehicle being repaired at no cost to you. Most automakers have a dedicated section on their websites where you can view any recalls pertaining to your vehicle, including Toyota. Technical service bulletins can also provide more information, such as when Hyundai addressed a known issue with the output speed sensor on models like the Elantra and Sonata.