P0720 is a generic OBD-II code that means the output speed sensor circuit in your transmission has a fault. The code often comes from a worn sensor, damaged wiring or low transmission fluid, not from a failed transmission. Check those causes before you approve any major repair.
What the P0720 Code Means
This code flags a fault in the output speed sensor circuit, which the powertrain control module (PCM) uses to decide when to shift. Because the code is generic, the same number can point to different parts depending on the make and model.
According to Kelley Blue Book’s code guide, the PCM relies on the output speed sensor signal to choose the transmission’s shift pattern. When that signal is wrong or missing, the PCM cannot shift as planned, and the driver feels it.
Related codes help narrow the problem. P0721 points to a sensor malfunction. P0722 and P0723 mean the PCM cannot predict when to shift correctly. If a scan shows any of these codes beside P0720, read them together before you choose a repair. A related transmission circuit code is covered in our P0740 code guide, and the generic transmission code is explained in our P0700 code guide.
Symptoms of a P0720 Code
The check engine light is usually the first sign of this code, followed by changes in how the transmission shifts. If the light is on but the car drives normally, the code may still be stored, so do not ignore it. Many drivers notice the shifting problem before they read the code.
- Rough or harsh shifts between gears (compare with transmission slipping symptoms)
- Engine misfires
- Stalling when the car comes to a complete stop
- Lower fuel economy than usual
Some of these symptoms also appear with other transmission faults. That is why a scan is the only reliable way to confirm that P0720 is the stored code on your vehicle.
What Causes P0720
A defective or damaged output or input speed sensor is the most common cause of P0720, according to Kelley Blue Book. The sensor itself is the first suspect, but it is not the only one.
The same source lists these other causes. A damaged PCM is the least likely of them.
- Corroded wiring near the speed sensor
- Loose or dirty connectors at the sensor or the harness
- Contaminated transmission fluid
- Defective shift solenoids (see transmission solenoid replacement cost) or other driveability sensors
- A damaged PCM, which is less likely
Why Transmission Fluid Matters
Low or dirty fluid can set the code even when the sensor is healthy. Check the fluid before you buy parts. Compare the level and condition with the specification in your owner’s manual or the service information for your vehicle. Mention the fluid condition to the technician, since contamination is one of the causes Kelley Blue Book lists.
How to Diagnose P0720 Step by Step
Diagnosis starts with a code scan and freeze frame data, then a road test, before any part is replaced. The freeze frame data records the conditions present when the code set, which helps the technician reproduce the fault.
- Scan the vehicle for stored codes and read the freeze frame data.
- Clear the codes (our guide to how to reset the check engine light explains the options), then road test the car to see whether the code returns.
- Inspect the wiring and connectors at the speed sensor for damage, corrosion or looseness.
- Check the transmission fluid for low volume or contamination.
- Test the sensor ground and reference voltage against the service manual specification.
Do not replace the sensor before the other causes are ruled out, since KBB warns against replacing it first. A basic code reader shows the code, but the voltage and resistance checks need the service data for your make and model.
Keep a record of each result. If the code returns after a repair, the record shows which cause was already cleared, so the next check starts in the right place.
Bring the same details to the shop: the code and any related codes, the freeze frame data, whether the code came back after clearing, the symptoms and when they happen, the fluid condition if you know it, and the exact year, make, model and engine. These details matter because a bulletin like the Infiniti one applies only to specific vehicles.
How to Fix P0720 by Cause
The right fix depends on the cause you find, so match the repair to the test results. The table below lists each likely cause, what to check and the usual repair.
| Cause | What to check | Usual repair |
|---|---|---|
| Output or input speed sensor | Signal and resistance at the sensor | Replace the sensor if testing confirms it |
| Corroded wiring or loose connector | Harness, pins and ground circuit | Clean, repair or replace the wiring or connector |
| Low or contaminated fluid | Fluid level and condition | Fluid service to the manufacturer specification |
| Shift solenoid | Solenoid resistance and operation | Replace the solenoid if testing confirms it |
| PCM | Every other cause ruled out first | Reprogram or replace the PCM as the last step |
Labor depends on where the sensor sits on your vehicle, so ask the shop to confirm the location before you approve the work. Costs vary widely by make, model and region, so compare written quotes instead of relying on a general figure. Ask for parts and labor on separate lines so you can compare quotes fairly. Replacing a whole transmission is extremely expensive, so it should be the last option, after the cheaper checks.
Why a Sensor Swap Alone Can Fail
On the 2014 to 2015 Infiniti Q50, a bulletin says to replace the control valve, not the output speed sensor, when diagnosis points to the sensor.
The Infiniti bulletin ITB19-040, published November 22, 2019, covers 2014 to 2015 Q50 cars (V37), not the Q50 Hybrid. It says that if DTC P0720 is stored, technicians should follow the diagnostic procedure in the electronic service manual. If that procedure leads to sensor replacement, the bulletin says to replace the control valve and not the output speed sensor.
This is a scope boundary. The bulletin covers one model and one range of years, so it does not describe how other makes handle this code. Check the service information for your own vehicle before you order parts.
A code that returns after a sensor swap is a clue, not a verdict. It can mean the new sensor is fine while the circuit, the connector or the fluid still has a fault. Test the circuit again before you assume the parts are the problem.
Can You Drive With a P0720 Code?
This code usually does not stop the car from being driven, but Kelley Blue Book advises against prolonged driving with the code set. The problem tends to get worse over time.
Left alone, the code can cause serious driveability problems. KBB also notes that it can lead to damage to the engine and the transmission, so a short drive to a shop is different from weeks of normal use.
- Rough shifting: have a technician inspect the vehicle right away.
- Stalling or misfires: arrange an inspection as soon as possible.
- Mild shifting issues only: book a scan and diagnosis soon.
If you cannot get an inspection right away, keep trips short and avoid hard use of the car until a technician has looked at it. That approach follows KBB’s warning against prolonged driving with the code set.
Frequently Asked Questions
Can I fix P0720 by replacing only the speed sensor?
Sometimes, but not always. A bad sensor is the most common cause, yet wiring, connectors, fluid and the PCM can also trigger the code. Test those first. On some Infiniti Q50 models, the bulletin says to replace the control valve instead of the sensor, so check the service data for your vehicle.
Does P0720 always mean the transmission is failing?
No. The code points to the output speed sensor circuit. Kelley Blue Book lists a defective sensor as the most common cause, followed by wiring, connectors, contaminated fluid and shift solenoids. A damaged PCM is less likely. Transmission replacement should come only after those checks fail, because it is extremely expensive.
What is the difference between P0720 and P0721?
This code means a problem in the output speed sensor circuit. P0721 specifically indicates a sensor malfunction. According to Kelley Blue Book, P0722 and P0723 mean the PCM cannot predict shifts correctly, so they are worth reading alongside this code.
Can low transmission fluid cause P0720?
Yes. Low or contaminated fluid is among the causes Kelley Blue Book lists. A fluid check is one of the first diagnosis steps before parts are replaced. Compare the level and condition with the specification for your vehicle.
Will clearing the code fix P0720?
Clearing the code only removes it from memory. If the fault is still present, the check engine light returns after a road test. Diagnose the cause first, then clear the code to confirm that the repair worked.
If the code keeps returning after a sensor or wiring repair, stop replacing parts and have a technician read the freeze frame data and test the circuit. Testing before more parts are swapped keeps the repair focused on the actual fault, and it gives the next shop a clear record to work from.
