The speed sensor on your car is an essential piece of a much larger system. By measuring the speed of your transmission, you can tell how fast you’re going at any moment. More importantly, other systems in your vehicle can use the readings from your speed sensor to figure out how the car should behave under different circumstances. 

Much like other sensors in your car, when the speed sensor fails, it triggers a check engine light code. In this case, it’s the P0720 code, which tells you that your output speed sensor circuit is malfunctioning. 

In this guide, we’ll show you how to diagnose and fix the P0720 code and anything else you might need to know about this particular error.

What is the P0720 Code, and What Does It Mean? 

The P0720 code is a diagnostic trouble code that means that your vehicle speed sensor or speed sensor circuit has failed. However, you should do some testing before you pull out the parts cannon. As it turns out, this code can be caused by a few other things. 

A speed sensor is a simple piece of technology that is essentially measuring how fast your transmission is spinning. It does so by using two components — a stator (the actual sensor) and the rotor. The latter usually comes in the form of a small sprocket wheel that sits somewhere inside your transmission. 

The stator is fixed in place and is positioned so that there’s a very tiny gap between it and the rotor. As each tooth of the sprocket passed in front of the stator, the sensor then measures the differences in the magnetic field caused by the gaps in the sprocket to determine how fast the transmission is spinning, and hence, how fast the vehicle is moving. 

What Causes a P0720 Fault Code? 

While there can be multiple causes for this fault code, the most obvious one is a dead speed sensor. Since the sensor works in tandem with the PCM (powertrain control module), a PCM failure or wire harness issues will also trigger a P0720 Fault Code. Some of the P0720 common causes are:

• Wiring circuit damage
• Speed sensor failure
• Faulty PCM
• Transmission fluid temperature sensor failure

Can Bad Transmission Fluid Cause P0720?

The short answer is, yes. As transmission fluid ages, it picks up dirt and coagulates. This sludge can accumulate on the speed sensor and cause it to malfunction. So it’s best to follow the manufacturer’s maintenance recommendations or replace your fluid earlier.

Where Is the Output Speed Sensor Located?

The purpose of such a sensor is to measure how fast your vehicle is traveling. The most common placement of the output speed sensor is near the transmission. Different car manufacturers make it easier or more difficult to access the speed sensor, so consult your car’s service manual for more information. 

What Are the Common Symptoms of P0720 Fault Code?

Unfortunately, because it can be a safety concern when this sensor fails, you should stop your car as soon as it is safe to. There are a few common symptoms that you will notice straight away when this issue arises:

• Check engine light
• Inaccurate speedometer reading
• Cruise control disengagement
• Clutch slipping
• Delayed, rough shifting
• Gear limitations

Transmission Issues

In a manual car, the driver controls the speed at which the car changes gear. In a torque converter and even DCT (Dual clutch transmission) car, the clutch engages at either a pre-programmed or most favorable speed and uses the speed sensor for this.

An automatic transmission uses the data from the speed sensor to know when to shift gears and what gear to shift into. Without this data, it can’t engage the clutch and will have trouble changing gears correctly because it doesn’t know how fast the driveshaft is moving.

Inaccurate speed data can cause your transmission to overheat and damage your clutch. However, The P0720 code is sometimes not caused by inaccurate speed data, but by a faulty transmission fluid temperature (TFT) sensor.

Some vehicles do not use a transmission fluid temperature sensor in conjunction with the speed sensor, so it’s best to consult your owner’s manual when diagnosing such an issue.

Speedometer Malfunction

Your speedometer uses the speed sensor reading to tell you how fast you’re going. As we drive, we tend to develop our ability to gauge how fast we’re going just by feel. If you notice that your instrument cluster indicated speed doesn’t feel right, there’s a good chance that you’re not seeing things. Instead, your vehicle speed sensor could be throwing bad data your way. 

How to Diagnose the Cause of P0720 Code 

In most cases, a sensor issue is easy to diagnose. As soon as it fails, the computer will log a fault, and you can begin your diagnosis process. First thing first, run a full scan. One diagnostic trouble code is fairly easy to deal with, but if there are several of them present at any given time, you could be looking at a more serious issue. 

Dash Lights

No car owner ever wants to see the check engine light of doom. However, it is the first step to diagnosing and repairing your vehicle, and a must that you pay attention to it.

Aside from the usual check engine light, your ABS and traction lights may also turn on. These lights can come on in modern vehicles because the ABS and traction sensors use the data from the speed sensor for their readings.

ODB II Reader

Your ODB II reader connects you directly to the brain of your vehicle. It allows you to easily diagnose any issues that occur during testing or any faults that have been stored during previous drive cycles.

Plug your ODB II reader into the port (usually under the passenger dash). After running your scan, the P0720 code will show on the fault log.

Multimeter

If you’ve only got the P0720 code, it’s safe to assume that your issue is most likely caused by a bad sensor itself. Even so, it’s always a good idea to test the potentially failed component before you start throwing parts at your car. 

When testing any electrical component, a multimeter is essential. Here, we will measure the voltage as the sensor is voltage-based.

First off, you need to identify the type of sensor that your car uses. Induction sensors use magnets, mechanical sensors use the hall effect or a small drive shaft connected to the transmission. The most common type of sensor is one that uses the hall effect. So we will focus our diagnosis on those.

Now, testing the wiring harness first allows us to ensure that the proper voltage is flowing from the battery. Ensure that your car is off before disconnecting the sensor.

Connect the positive (red) multimeter probe to the positive port of the wiring harness connector. A wiring diagram will help you identify which wire is ground, positive, and signal.

Your car should be on but not started. Connect the black probe to the ground. Any piece of your car’s chassis or body will suffice as well. Your multimeter should read battery power, or around 12V when you turn the key to the accessory position. 

TFT Sensor 

Even a transmission fluid temperature sensor isn’t a common cause of the P0720 code, it can be. Knowing how to test this sensor can come in handy should ever run out of ideas when diagnosing the P0720 code. The TFT sensor is a resistance-based sensor, so you’ll need a multimeter to test it. 

Always consult your wiring diagram before measuring any resistance or voltage as the harnesses differ in certain cars. Identify the transmission fluid sensor pins on the wiring harness.

The resistance differs widely based on the temperature input on the sensor. Your reading should be between 800 ohms – 5000 ohms, and between 231 °F – 130 °F, respectively.

You can also test the ground in the same manner as the speed sensor. The voltage should be 5V without the car being turned on and 12V when it’s on.

How to Fix P0720 Code 

The root cause of the problem needs to be solved before you can fix the code. If you’ve diagnosed the issue, replaced the sensor and wiring, checked the TFT sensor, and the code is still showing up, you could be looking at PCM or transmission failure.

A malfunctioning control module or a transmission failure will manifest as a P0720 Code, usually accompanied by a few other codes. Although these are separate issues that require specific diagnoses, these are the parts that should be looked at post-sensor replacement.

Does P0720 Clear Itself?

P0720 is a permanent DTC code. Depending on your vehicle, a short drive may clear the code if everything is functioning properly. It’s always helpful to check if you can clear the code using an ODB reader, so if you can, do that before driving your car.

Can You Drive with P0720 Code?

No, it’s a safety hazard to drive with a speed sensor failure. Not only because you can’t tell how fast your car is traveling, but because you might blow your transmission.

Get Quality Parts For Your Car 

Maintaining and repairing your car is something we know you take pride in. Whether it’s fluids, tires, sensors, or any other part, you only use the highest quality components.

At eEuroparts.com, we supply everything you could need to do proper maintenance on your car. Genuine, OEM, or aftermarket parts are only a few clicks away. Select your car using our vehicle selection tool, and search for the parts you need. You’ll be presented with a list of parts that are a guaranteed fit for your specific vehicle!