P0720 Code: Output Speed Sensor Circuit

Dealing with a P0720 code? This guide will help you understand what code P0720 means, what triggers it, and what you can do to diagnose and fix the underlying issue that is causing it to be stored in your vehicle’s computer.

What Does Code P0720 Mean?

Code P0720 is a diagnostic trouble code (DTC) that means your vehicle’s onboard computer has detected an error from the output speed sensor (OSS). Also known as the output shaft sensor, the OSS monitors the speed of the transmission’s output shaft. If it sends an erratic or slow response to the engine control module, it will activate the check engine light and store the P0720 code.

It should be noted that the P0720 is a general indicator of an error from the output speed sensor and does not identify its exact cause. It usually appears with other more specific transmission or engine codes.

What Causes Code P0720?

On modern automatic transmissions/transaxles, the powertrain control module (PCM) / transmission control module (TCM) continually measures engine rpm, turbine shaft speed, and output shaft speed.

Code P0720 can have several causes, with the most common being a faulty output shaft speed sensor. Damaged or loose wiring is another possible cause.

A malfunctioning PCM or TCM can also cause the code to be set, although this is less likely to occur.

Code P0720 can also appear partly due to damaged or worn transmission components. In such cases, the damage is usually severe enough to disrupt the output speed sensor’s signal and likely set other error codes.

• Faulty output speed sensor
• Damaged or loose wires
• Dirty transmission fluid
• Malfunctioning ECM
  

Faulty Output Speed Sensor

A damaged or defective OSS can send inaccurate or intermittent signals to the engine control module (ECM), which triggers the code to appear.

Damaged or Loose Wires

Frayed, corroded, or loose wires can impede the connection of the OSS to the ECM.

Dirty Transmission Fluid

Old or contaminated transmission fluid can also be a cause. Metal filings found in the fluid from component wear can stick to the sensor’s magnetic tip and affect its readings.

Malfunctioning ECM

In rare cases, a software glitch, corrupted drivers, or a hardware failure can cause the electronic ECM to set a P0720 code by mistake.

What Are the Symptoms of Code P0720?

The first symptom of a code P0720 is often the check engine light illuminating on the dashboard. You may also notice a drop in shifting quality and fuel economy or get incorrect readings from the speedometer.

If you notice any of these symptoms in your vehicle, it’s recommended that you have it diagnosed as soon as possible.

• Check engine light is on
• Rough shifting
• Poor fuel economy
• Speedometer issues

Check Engine Light is On

Also known as the malfunction indicator lamp, the check engine light automatically switches on once an error code is set.

Rough Shifting

Shifting between gears may start to feel rough or uncomfortable. The transmission may also slip or fail to shift gears.

Poor Fuel Economy

Issues with shift quality can cause the engine to work harder or struggle to maintain speed, resulting in higher fuel consumption.

Speedometer Issues

If code P0720 is being caused by a faulty output speed sensor, you may notice the speedometer displaying inaccurate or zero readings.

How to Diagnose Code P0720

If you have the time and equipment, you can diagnose the cause of the code P0720 yourself. Some of the troubleshooting steps you can take include:

Retrieve and Analyze Codes

Using an OBD-II scan tool, scan for and retrieve any error codes stored in your vehicle aside from P0720. These codes can help shed light on what exactly is causing code P0720 to appear.

Inspect the Wires and Connectors

Check the wiring harness for frays, cuts, corrosion, water intrusion, or other signs of damage that might disrupt the signal. You can also use a multimeter to check for current and resistance on the wires.

Check the Output Speed Sensor

Carefully remove the sensor and check for dirt buildup or signs of damage.

Inspect the Transmission Fluid

Check for low fluid levels or signs of contamination. As a rule of thumb, if the transmission fluid appears and smells burnt, it’s already gone bad and must be changed.

Examine the ECM

If the parts mentioned above have no issues, the ECM may be at fault. Carefully remove the module and check it for bent pins, corrosion, or other signs of damage. You can also take the module to a repair shop for more advanced diagnostics.

How to Fix Code P0720

Fixing code P0720 can vary depending on what’s causing it to appear. Some of the common repairs are:

Change the Transmission Fluid

Dirty and contaminated transmission fluid should be drained and changed with a new filter.

Clean or Replace the Output Speed Sensor

Carefully remove any dirt or debris from the sensor using a clean cloth and electrical contact cleaner. However, if the sensor is severely dirty or damaged, it must be replaced.

Repair or Replace Wiring and Connections

Tighten any loose connections and remove minor rust spots on metal contacts with contact cleaner. Replace any wires that are frayed, corroded, or severely damaged.

Repair or Replace the Engine Control Module

Outdated or corrupted ECM software can be updated and reprogrammed, but in case of severe software or hardware failure, it must also be replaced.

Other Codes Related to P0720

Code P0720 is closely related to and often appears with several error codes. These include:

P0721

This diagnostic code indicates a malfunction in the output speed sensor or its circuit.

P0722

This code means the output sensor is not sending any signals, and the ECM doesn’t know whether to shift up or down.

P0723

This code is similar to P0722, except that the output speed sensor sends an inconsistent signal to the ECM.