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Code P0720. Causes, Symptoms, Diagnosis and Repair

The P0720 code It is defined as a malfunction of the output speed sensor circuit, causing vehicle performance problems such as hesitation when accelerating, engine stalling, and misfires.

Most OBD-II-equipped cars use an output speed sensor to provide the PCM with a transmission output speed signal.

Let’s see more details about this code, its meaning, its symptoms, its causes, how to diagnose it, and how to repair it. Stay with us.

Output Speed ​​Sensor Operation

On most models, the sensor threads directly into the transmission housing or mounts to the outside of the transmission housing using bolts.

The sensor is an electromagnetic design and uses a reluctor ring (or a specialized set of splines) on the output shaft as reference points.

As the output shaft rotates under the action of the motor, the electromagnetic output speed sensor uses the spaces between the splines to provide voltage signal interruptions in the circuit.

The PCM receives these interruptions as square waveform patterns of various degrees of voltage and translates them into transmission output speed.

After that, the PCM will compare the transmission output speed data with the engine input speed data to determine shift patterns as well as certain engine driving functions.

Output speed sensor Typical uses a three-wire connector, but you should inspect your car’s wiring diagram to confirm its specific layout.

The first wire is a signal reference voltage (usually 5 volts), the second wire will typically be a ground wire, and the signal wire will be the third wire.

As the reluctor ring passes the electromagnetic sensor, the 5-volt reference signal is completed by the protruding metal surfaces.

The recessed surfaces of the reluctor provide voltage interruptions and these interruptions are sent to the PCM via the signal cable.

What is the P0720 code?

Error code P0720 occurs when the PCM detects a problem in the car’s output speed sensor circuit.

The PCM relies on the signal from the output speed sensor, which it uses to determine the correct shift strategy and then send that information to the transmission.

If the PCM is unable to receive information from the output speed sensor, or the information is erratic, sporadic, or simply not increasing slowly and steadily, then it will trigger error code P0720.

Output speed sensors detect speed by using the revolution of the output gear, which is also the parking pawl gear.

This is used as a reluctor for the PM generator or a Hall effect sensor, which creates a square or sine wave pulse signal. The pulse signal is sent to the control module (TCM or PCM) which processes it as the speed of the car.

Any time you diagnose a 700 series DTC with a transmission, transfer case, or other driveline components, check to see if another DTC is active.

Module communications DTCs are “U” codes. These are most often found when looking for DTCs under the chassis or body systems.

Chassis-related codes are labeled “C” and body system-related codes are labeled “B” codes.

These can cause powertrain problems if they affect a sensor that is also used by the heating and air conditioning system.

You may also be interested in Error Code P0733: Incorrect Gear Ratio 3

What Are the Common Causes of Code P0720?

This type of failure is specific to a particular system, and its location is easily detectable. The most common causes of this code are the following:

  • Defective output speed sensor.
  • Faulty input speed sensor.
  • Damaged or corroded cables or loose connectors.
  • Defective engine drivability sensors.
  • Contaminated, dirty, or low transmission fluid.
  • Malfunctioning shift solenoid.
  • Defective PCM.
  • Control module (TCM or PCM) wiring is open or shorted.

What Are the Symptoms of Code P0720?

As with other error codes, the code P0720 activates the Check Engine light and records the code in the vehicle’s memory system.

Other symptoms include engine and transmission problems, see below for a list of symptoms.

  • Erratic or malfunctioning speedometer.
  • Inability to change gear or sudden changes.
  • Hesitation in acceleration.
  • The “Check Engine” light or MIL comes on.
  • High fuel consumption.
  • Engine stalling.

How to Diagnose the P0720 Code

Here are some steps you should follow to diagnose this fault code:

  • An OBD2 scanner, digital volt/ohmmeter, and possibly an oscilloscope will be helpful in making a successful diagnosis.

Visual inspection

  1. Begin your diagnosis with a visual inspection of the wiring, connectors, and system components.
  2. Repair or replace any open, shorted, damaged or corroded items as necessary.
  3. Retest the system to ensure repairs were completed correctly.
  4. Pay special attention to wiring and connectors that have become contaminated due to leaking engine oil or transmission fluid, burned on hot exhaust pipes, or damaged due to road debris.

Scan the car

  1. If the wiring, connectors, and system components appear to function normally, connect the scanner to the diagnostic connector and record all stored trouble codes and freeze the frame data.
  2. This information can be extremely useful in diagnosing intermittent conditions that may have contributed to this code being stored.
  3. Now, once all the codes have been cleared, you must operate the vehicle to see if the code returns.
  4. If the code does not return immediately, you may have an intermittent condition.
  5. Intermittent conditions can be challenging to diagnose and, in extreme cases, may need to be allowed to worsen before a correct diagnosis can be made.
  6. If the code returns immediately, then the reference voltage and ground signals should be checked at output speed sensor.

Electrical inspection with a multimeter

  1. If the reference voltage or ground circuits are open, use the digital volt/ohmmeter to check continuity.
  2. Disconnect all related control modules from the circuit before checking the resistance of the circuit, or damage to the controller and resistance in both circuits may occur.
  3. Repair or replace system circuits/connectors as necessary and retest the system to ensure repairs were completed correctly.
  4. Using the manufacturer’s wiring diagram for the output speed sensor, test the resistance and continuity of all related circuits and the sensor, and compare the results to the manufacturer’s specifications.
  5. Repair or replace circuits, connectors, and system components that do not meet manufacturer specifications.

Electrical inspection with oscilloscope

  1. Always retest the system to ensure a successful repair. If all system circuits are intact, connect the oscilloscope and observe the live streaming output speed sensor data.
  2. You should watch for faults or “weak spots” in the waveform pattern and repair or replace circuits, connectors, or system components as necessary.
  3. If all circuits match the manufacturer’s specifications and the waveform pattern is within acceptable limits, then it is the PCM that is defective.
  4. You should note that PCM failure is rare and replacement will require reprogramming.

Common Errors When Diagnosing Code P0720

Most people do not follow the correct protocol for diagnosing trouble codes, resulting in errors and failure to resolve the fault.

It is very important to follow the steps in the correct order to ensure that the inspection and repair is thorough and efficient.

If the trouble code diagnostic protocol is not followed correctly, it will result in the replacement of a component that does not need repair, and failure to occur.

How to Fix Code P0720

Repairs for this code are fairly easy, but of course, require proper diagnosis. Everything will depend on the results of the diagnosis. Common repairs include:

  • Replacing the output speed sensor.
  • Replacing the input speed sensor.
  • Replacing connectors or cables.
  • Drain and change the transmission fluid.
  • Replacing the PCM module.

Can I Drive The Car With The P0720 Code Activated?

In most cases, error code P0720 It will not prevent you from being able to drive the car, although it will be difficult for you to keep it on the road safely.

The effects of the failure could become increasingly worse if not repaired as soon as possible, which can cause further damage to the transmission. We recommend that you take immediate action and carry out diagnosis and repair.

How Can I Avoid Code P0720?

Many times this code occurs due to a wiring fault or problems with the condition of the transmission fluid. In these cases, this failure is perfectly avoidable with a routine inspection of the system.

By routinely performing a visual inspection of your car’s systems, you can identify wiring problems before failure occurs.

Likewise, if you check the condition of the transmission fluid and notice that it is dark, inconsistent or dirty, you should change it immediately.

As for the sensors, if they fail, you can only diagnose it through the scanner. In general, these sensors have a long useful life although they are not free from failures.


You may also be interested in Error Code P0725: What Does It Mean and What to Do?

The P0720 code It may involve an expensive or simple repair, this will depend on the results of the diagnosis. Our recommendation is that, when you detect this fault code, you should take the car for repair immediately, to avoid a major fault.

If you have the necessary knowledge, you can carry out the diagnosis and repair yourself, but if you feel that you do not have a good grasp of the information, we recommend that you take the car to a specialized service.

If you want to know other articles similar to Code P0720. Causes, Symptoms, Diagnosis and Repair you can visit the category Fault Codes.


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