700 series codes such as the P0720 are typically transmission-related codes stored by the ECM or PCM. The ECM is a module that controls only the engine, and on vehicles with automatic transmissions there will be a Transmission Control Module (TCM) that communicates with the ECM.
A PCM (Powertrain Control Module) controls both the engine and the transmission. Thus, we refer to the ECM/PCM in these articles when discussing the primary on-board computer, but a growing number of vehicles tends to have separate Engine and Transmission Control modules that communicate with each other over the CAN bus. Thus, you may have an ECM and a TCM but the ECM may display DTCs that are TCM related – like this one.
However, having the DTCs won’t make a difference if you don’t know what they mean. So, if you’re getting the code P0720, this article will help point you in the right direction.
What Does the P0720 Code Mean?
The P0720 code is activated when the PCM detects insufficient or erratic input from the output shaft sensor (OSS). This code is similar to P0721, P0722, and P0723.
Diagnostic trouble code (DTC) P0720 stands for “Output Speed Sensor Circuit Malfunction.” It is stored when the ECM/PCM/TCM perceives a problem with the output speed sensor or its circuit. If, for example, the engine speed and input shaft speed are at a certain RPM but the output shaft speed is erratic or not what the computer expects, P0720 will be stored. There may also be a P0500 code stored on some platforms.
Speed Inputs and DTC Codes
In order for the Transmission Control System (ECM/TCM/PCM, etc.) to operate correctly and detect mechanical or electrical transmission concerns, there are multiple speed inputs factored into the algorithms written into the computer(s).
First, the engine speed is factored in, because that’s important, and that information comes from the engine’s crankshaft sensor. The transmission input shaft (the turbine shaft connected to the torque converter turbine) speed is also measured. Some transmissions will include an intermediate shaft speed sensor, but all electronically controlled automatic transmissions will have an output shaft sensor that sometimes doubles as the vehicle speed sensor.
Each of the speed sensors typically reads a toothed wheel mounted or machined on the rotating component, because that’s how speed sensors work.
Depending on the type of sensor used on the vehicle in question, the signal sent to the ECM/PCM/TCM may be an analog AC signal or a DC digital square wave.
What are the Possible Causes of the P0720 Code?
Here are the probable causes of code P0720:
- Faulty output shaft speed sensor
- Open or short in the electrical wiring or connections
- Malfunctioning PCM
What are the Common Symptoms of the P0720 Code?
The manifestations of a triggered P0720 code activated usually involve changes in the driveability of your car.
Here are the most common symptoms you may encounter if the PCM is detecting a P0720:
- Delayed or no gear shifting
- Malfunctioning speedometer and cruise control
- Sometimes accompanied by P0715 or P0500
How to Diagnose the P0720 Code
There are several possible causes that could trigger the P0720 code, so diagnosing it is not a straightforward affair. This is why a lot of people leave the job to their mechanics.
If you would prefer to do it yourself, however, watch these videos to get a better understanding of how to diagnose this code:
How to Fix the P0720 Code
As with diagnosis, fixing the P0720 code could be a little tricky since there’s no one-size-fits-all solution for resolving the code. You can have your mechanic do the fix for you or you can decide to go for it yourself if you feel like you have the required DIY skills.
If you’re planning on doing the latter, you’ll need to do some research. Once you’ve diagnosed the underlying cause, go online to find out what repairs other people (with the same vehicle as yourself) have employed to clear this code.
You should be able to find good information on forums and other similar platforms—just make sure to stick to the resolutions shared by owners of the same vehicle, as the appropriate fix for a P0720 may vary depending on make and/or model. A P0720 fix for a Ford, for instance, may not be the same as that of the repair you may need to do on a Nissan.
When you’re ready to perform the fix, make sure to check out repair manuals like the ones by Chilton or Haynes to figure out the proper steps for repairing your vehicle. You can also try a single-vehicle ALLDATA subscription that should help you with this and any other repairs you may need to do in the future.
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