P0720 Causes: What Triggers an Output Speed Sensor Circuit Malfunction?
Quick Answer
P0720 means the vehicle’s computer has detected a problem in the output speed sensor circuit. The most common causes are a failed output speed sensor, damaged wiring, loose or corroded connectors, signal problems, or a vehicle-specific transmission control fault. An OBD diagnostic code identifies the affected circuit, but it does not prove which part has failed.
Common P0720 causes
- Failed speed sensor: The output shaft speed sensor may stop producing a usable signal.
- Damaged wiring: An open circuit, short, rubbed wire, or excessive resistance can interrupt the signal.
- Connector problems: Moisture, corrosion, bent pins, or a loose plug can create an intermittent fault.
- Signal wheel damage: A damaged reluctor, tone wheel, or sensor drive gear can produce an incorrect speed signal on some transmissions.
- Shared circuit fault: Some vehicles combine related transmission sensors or wiring, allowing another fault to affect the output-speed signal.
- Vehicle-specific fault: Certain transmissions can set P0720 because of valve-body, control-module, or internal transmission issues.
Best first check
- Scan for companion codes and inspect live output-speed data before buying a replacement sensor.
P0720 can look simple on an OBD2 scanner, but replacing the sensor immediately is often a mistake. I treat it as a circuit diagnosis first because the sensor is only one part of that circuit.
This guide explains the likely causes, symptoms, diagnostic order, and common repair mistakes. It also shows when a transmission-specific service bulletin can completely change the repair.
In This Guide
What Does P0720 Mean?
P0720 means Output Speed Sensor Circuit Malfunction. It is a powertrain diagnostic trouble code associated with the transmission output-speed signal.
Definition: The output speed sensor measures how quickly the transmission output shaft is rotating and sends that information to the vehicle’s control system.
The control module can use output-speed information when calculating shift timing and other transmission functions. Depending on the vehicle, related information may also affect the speedometer or other systems.
The important word in P0720 is circuit. A scanner is telling you that the expected signal has a problem, not that the sensor has automatically failed.
- P0720: Output speed sensor circuit malfunction.
- P0721: Output speed sensor range or performance problem.
- P0722: Output speed sensor circuit has no signal.
- P0723: Output speed sensor signal is intermittent.
Those neighboring codes can provide useful context. If several appear together, I pay close attention to shared wiring, connectors, power supplies, and transmission harnesses.
An OBD2 scanner is therefore the beginning of the diagnosis. It isn’t a parts-ordering machine.
What Are the Most Common P0720 Causes?
The most likely P0720 causes involve the sensor itself or the electrical path carrying its signal. Vehicle-specific transmission designs can add other possibilities.
1. Failed output speed sensor
An output speed sensor can fail electrically or stop producing a clean signal. Age, heat, contamination, or internal component failure can contribute.
A bad sensor may produce no output, an intermittent signal, or a value that doesn’t agree with actual vehicle operation. However, testing should come before replacement.
2. Damaged output speed sensor wiring
Transmission wiring lives in a rough environment. Heat, vibration, road debris, oil contamination, previous repairs, and rubbing against brackets can damage the harness.
- Broken or partially broken wires
- Shorts to ground
- Shorts to another circuit
- Excessive resistance
- Pinched or stretched wiring
- Damaged insulation near the transmission
I pay extra attention to areas where a harness changes direction or passes near metal edges. A wire can look intact outside while individual conductors have broken inside.
3. Loose, contaminated, or corroded connector
A good sensor cannot send reliable information through a bad connection. Moisture or corrosion inside the connector can create resistance or an intermittent signal.
Check the terminals for discoloration, pushed-back pins, bent contacts, oil contamination, or a connector that does not lock firmly. Gently moving the harness while watching live scan data can sometimes expose an intermittent connection.
4. Damaged reluctor, tone wheel, or sensor gear
The sensor needs a rotating reference to generate useful speed information. Depending on transmission design, that reference may be a reluctor wheel, tone wheel, magnetic target, or driven gear.
Damage to that component can distort the signal even when the electrical sensor passes a basic resistance check. That’s one reason an ohmmeter reading alone may not settle the diagnosis.
5. Related transmission sensor or shared-harness problem
Some transmission designs place several sensors inside the same harness or assembly. A problem with internal wiring can therefore affect more than one sensor circuit.
Look at every stored transmission code rather than isolating P0720. Codes involving temperature or other speed sensors may reveal a common electrical problem.
6. Transmission control or valve-body fault on certain vehicles
This is where generic parts swapping gets expensive. P0720 does not always mean the external output speed sensor should be replaced.
For example, an Infiniti service bulletin for certain 2014–2015 Q50 models tells technicians to follow the factory diagnostic procedure. If diagnosis leads toward output-speed-sensor replacement, the bulletin specifies a control-valve repair instead.
You can search NHTSA manufacturer communications for technical information that may apply to a specific year, make, and model.
Locksmith’s note: Never assume a repair procedure applies just because another vehicle has the same P0720 code. Transmission hardware and control strategies vary substantially between models.
| Possible cause | Clue to look for | Useful verification |
|---|---|---|
| Output speed sensor | Missing or implausible output-speed data | Live data and factory-specified electrical testing |
| Wiring | Rubbed insulation, open circuit, intermittent reading | Continuity, voltage, ground, and harness inspection |
| Connector | Corrosion, moisture, bent or loose terminals | Terminal inspection and circuit testing |
| Tone wheel or gear | Erratic signal despite an electrically sound sensor | Physical inspection or waveform testing |
| Vehicle-specific transmission fault | Known service bulletin or additional transmission codes | Factory service information and model-specific diagnosis |
Section Takeaway: P0720 identifies an output-speed circuit problem, not a guaranteed failed sensor. Test the sensor, wiring, connectors, signal source, and vehicle-specific possibilities before replacing parts.
What Symptoms Can P0720 Cause?
P0720 symptoms range from a check engine light with little noticeable change to harsh shifting and reduced performance. The exact behavior depends heavily on how the vehicle uses the output-speed signal.
- Check engine light: The powertrain controller stores P0720 after detecting the circuit fault.
- Delayed or abnormal shifting: Incorrect speed information can interfere with transmission shift decisions.
- Harsh shifts: Some vehicles may shift firmly or unexpectedly when the normal speed signal is unavailable.
- Reduced-power behavior: A control system may use substitute values or a protective operating strategy.
- Speedometer problems: On some designs, an output-speed fault may affect the displayed vehicle speed.
- Transmission warning: Some vehicles illuminate a separate transmission or drivetrain warning.
You may also find P0720 even though the vehicle appears to drive normally. Intermittent wiring faults are especially capable of setting a code before the driver notices a consistent symptom.
Don’t judge severity from the warning light alone. AAA notes that diagnostic trouble codes provide clues to the problem and still require proper diagnosis before parts are replaced.
If the vehicle is shifting violently, losing power, or otherwise behaving abnormally, stop treating P0720 as a simple warning-light issue. Have the transmission inspected before normal driving continues.
How Do You Diagnose P0720 Correctly?
The best P0720 diagnostic process moves from information gathering to electrical testing. I avoid replacing anything until I know what the scanner and circuit are telling me.
- Scan every module you can access. Record P0720 plus any related transmission, communication, speed-sensor, or voltage codes.
- Save freeze-frame information. Vehicle speed, engine speed, temperature, and operating conditions can show when the fault appeared.
- Check live output-speed data. Look for a signal that is missing, frozen, erratic, or inconsistent with vehicle movement.
- Inspect the connector. Check for corrosion, contamination, damaged pins, loose terminals, or a broken locking tab.
- Inspect the harness. Follow accessible wiring and look for rubbing, heat damage, stretching, repairs, or contact with sharp surfaces.
- Test the circuit to factory specifications. Use the correct wiring diagram and service data for that exact year, engine, and transmission.
- Check the sensor and signal source. Confirm the sensor can produce the type of signal expected by the vehicle.
- Review technical service information. A manufacturer bulletin may identify a known failure pattern that changes the repair path.
Pro tip: Don’t use resistance values, wire colors, reference voltages, or pin locations from a different vehicle. Confirm all electrical specifications against factory information for your exact application.
As of 2026, even inexpensive scanners can retrieve generic OBD2 codes, but advanced diagnosis may require transmission live data. A basic reader that only displays “P0720” cannot tell you whether the sensor signal is dropping out while driving.
Also check your VIN for relevant campaigns or manufacturer information through the NHTSA recall lookup. A recall and a technical service bulletin are not the same thing, but checking by VIN helps rule out known safety recall issues.
Never perform a driven-wheel test with a vehicle insecurely supported. If testing requires the wheels to rotate while raised, professional equipment and proper safety procedures are essential.
Can You Drive With P0720, and What Usually Fixes It?
Whether you should keep driving depends on the symptoms, not the code number alone. A vehicle that shifts normally presents a different situation from one that slams into gear, loses power, or enters a protective mode.
AAA recommends prompt diagnosis when the check engine light appears, especially if the vehicle also behaves abnormally. Their check engine light guidance also advises stopping when significant drivability symptoms make continued operation unsafe.
Repairs that may solve P0720
- Replacing a confirmed faulty output speed sensor
- Repairing damaged sensor wiring
- Cleaning or replacing a damaged connector or terminals
- Repairing a poor ground, reference, or signal circuit
- Replacing a damaged sensor gear or signal wheel where applicable
- Repairing an internal transmission harness where diagnosis confirms the fault
- Performing a vehicle-specific valve-body or control-system repair when factory information requires it
The repair should match the test result. Clearing the code without correcting the cause may only make the warning disappear temporarily.
What should you avoid?
Don’t replace the transmission just because the code belongs to the P07xx transmission family. P0720 can be caused by something as localized as a damaged wire or connector.
Don’t replace the output speed sensor solely because its name appears in the code description. A circuit code requires a circuit diagnosis.
A real example appears in an NHTSA-hosted Infiniti bulletin covering certain 2014–2015 Q50 vehicles. That bulletin specifically warns technicians not to make a simple output-speed-sensor replacement when its stated diagnostic conditions apply.
Locksmith’s note: If the vehicle has harsh shifting, repeated limp-mode operation, multiple transmission codes, or inaccessible internal wiring, professional diagnosis is usually safer than continued parts swapping.
P0720 Frequently Asked Questions
Does P0720 always mean the output speed sensor is bad?
No. P0720 describes a malfunction in the output speed sensor circuit. The sensor can fail, but wiring damage, connector corrosion, signal-wheel problems, internal harness faults, and vehicle-specific transmission issues can produce the same code.
Can bad wiring cause a P0720 code?
Yes. An open wire, short circuit, damaged insulation, high resistance, loose terminal, or corroded connector can prevent the control module from receiving a valid output-speed signal.
Can a bad transmission cause P0720?
It can on some vehicles, but P0720 alone does not prove the transmission has mechanically failed. Check the sensor circuit and factory service information before assuming an expensive internal transmission problem.
Can low transmission fluid cause P0720?
Low fluid can cause transmission performance problems, but it isn’t the first generic cause I would assume for an output-speed sensor circuit malfunction. Check the fluid according to manufacturer procedures while diagnosing the actual electrical or signal fault.
Can I clear P0720 with an OBD2 scanner?
Most compatible scanners can clear a stored powertrain code, but clearing it does not repair the cause. If the fault remains, the control module can detect it again and P0720 may return.
What codes are related to P0720?
P0721, P0722, and P0723 are closely related output speed sensor codes. Other transmission or electrical codes stored at the same time can provide important clues about shared wiring, sensor signals, or control-system problems.
Should I replace the speed sensor first?
Not without testing. Check live data, wiring, connector condition, related codes, and factory diagnostic information first. That approach reduces the chance of replacing a working sensor while leaving the actual circuit fault untouched.
P0720 is best approached as an electrical and signal diagnosis, not a sensor-replacement instruction. Read every stored code, inspect the circuit, compare live data, and use service information for your exact year, make, model, and transmission.
If the vehicle is shifting harshly or losing power, avoid unnecessary driving until the fault has been diagnosed. A few careful checks can separate a simple wiring repair from a transmission-specific problem before unnecessary parts are purchased.
