# P0720: Output Shaft Speed Sensor "A" Circuit **Verdict:** Drive to a shop this week Transmission - Generic OBD-II code, applies to all gasoline cars and light trucks sold in the US since 1996. - **Typical cost:** $100-$750 - **Urgency:** This week - **Most likely:** Failed output speed sensor or wiring - **DIY?:** Possible if reachable ## Quick answer P0720 means the transmission computer has a problem with the signal from the output speed sensor, which measures how fast the shaft leaving the transmission turns. On many vehicles this sensor also drives the speedometer, so the speedometer may act up along with harsh shifting. A failed sensor, damaged wiring, or a corroded connector are the usual causes. ## What does P0720 mean? The output speed sensor reads the speed of the transmission's output shaft, which is tied directly to wheel speed through the driveshaft or axles. The transmission computer compares it with input speed to confirm which gear it is in, judge slip, and time shifts. On many rear-wheel-drive trucks and some cars, the same signal serves as the vehicle speed signal for the speedometer and cruise control, while other vehicles use wheel speed sensors instead. P0720 sets when the output speed signal is missing, erratic, or does not make sense compared with other speed signals, such as wheel speeds from the ABS module, for a set time while driving. Exact tests vary by maker, and some use P0721 through P0723 for more specific faults. "A" marks the first or only output speed sensor. "Circuit" means the cause could be the sensor, its wiring, the connector, or the computer reading it. ## What are the symptoms of P0720? - Speedometer jumpy, dropping to zero, or dead on some vehicles - Harsh, early, late, or erratic shifts - Limp mode with the transmission stuck in one gear - Cruise control not working - Check engine light, sometimes ABS or traction control lights ## What causes P0720? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Failed output speed sensor** (most common). The sensor sits low on the transmission or transfer case, close to heat and road spray, and its coil or electronics can fail over time. An erratic or dropping signal, especially once the transmission is hot, is typical. A scan tool showing output speed jumping while the ABS wheel speeds stay smooth points straight at the sensor. 2. **Wiring or connector problem** (common). The output sensor wiring often runs along the bottom of the transmission, where road debris can hit it, brackets can chafe it, and the exhaust can melt it. Water and salt corrode the connector pins. A signal that cuts out over bumps or only in wet weather usually points to the wiring rather than the sensor itself. 3. **Metal debris on the sensor tip** (less common). Many output sensors are magnetic, and fine metal particles from normal gear wear collect on the tip. A thick coating can weaken or distort the signal. Cleaning the tip may restore it for a while, but heavy shavings suggest internal wear, so the fluid and the pan should be checked before the car goes back into service. 4. **Damaged reluctor ring or loose sensor** (less common). The sensor reads a toothed ring on the output shaft or a nearby gear. A cracked or damaged ring, a sensor that has worked loose, or a wrong air gap after repair can produce a missing or noisy signal. Speedometer trouble that started right after transmission, driveshaft, or transfer case work is a strong clue here. 5. **Computer or network fault** (rare). Rarely, the transmission computer or the module that shares vehicle speed fails or needs a software update. Because several modules use vehicle speed, a network communication fault can also make the signal look wrong to some of them. A shop checks the signal at the computer connector before replacing anything expensive. ## How do you diagnose P0720? 1. Read codes in the transmission, engine, and ABS modules. 2. Compare output speed with the ABS wheel speeds on a scan tool while driving. 3. Inspect the sensor, connector, and harness for damage, corrosion, or fluid, and check the sensor tip for metal debris. 4. Test the sensor's resistance or supply voltage and the wiring back to the computer. ## How do you fix P0720, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Repair wiring or connector | $100-$350 | Common on vehicles in road-salt states. | | Replace output speed sensor | $150-$400 | Typically a single bolt-in sensor; any lost fluid is topped up. | | Transmission fluid and filter service | $150-$350 | Worth adding if heavy metal debris was found on the sensor. | Full price breakdowns: [transmission fluid change cost](/cost/transmission-fluid-change). ## Is it safe to drive with P0720? > **Drive to a shop this week.** You can usually drive carefully to a shop, but the speedometer may be wrong and shifts may be harsh or limited. Check your speed with a phone GPS app, avoid highways if the car is in limp mode, and do not rely on cruise control. ## Will P0720 fail an emissions test? P0720 turns on the check engine light, which fails an OBD-II emissions test in most states. Several readiness monitors need a valid vehicle speed signal to run, so an output sensor fault can keep monitors not ready even after codes are cleared. Fix it before scheduling the test. ## After the repair: clearing P0720 After the repair, clear codes in every module that stored them, then test drive. The speedometer should closely match a GPS speed reading, and on a scan tool output speed should track the ABS wheel speeds without dropouts. Normal shifting and no returning code over several drives, including highway speeds, mean the repair worked. ## How to prevent P0720 - Have the transmission fluid changed on schedule so less metal collects on sensor tips. - Ask the shop to check sensor wiring clips after transmission, driveshaft, or exhaust work. - Rinse road salt from the underbody during winter in states that salt roads. - Get a jumpy speedometer checked early, before the signal fails completely and triggers limp mode. ## Codes often seen with P0720 - [P0500](/codes/p0500): Vehicle Speed Sensor "A" - [P0715](/codes/p0715): Input/Turbine Speed Sensor "A" Circuit - [P0717](/codes/p0717): Input/Turbine Speed Sensor "A" Circuit No Signal - [P0700](/codes/p0700): Transmission Control System (MIL Request) - [P0730](/codes/p0730): Incorrect Gear Ratio ## Frequently asked questions ### Can I drive with a P0720 code? You can usually drive carefully to a shop, but expect harsh shifts or limp mode, and on many vehicles a speedometer you cannot trust. Use a GPS app to check your speed, avoid highways if the car will not upshift, and get it repaired soon to avoid transmission wear. ### What is the difference between P0720 and P0500? P0720 points to the transmission's output speed sensor circuit, while P0500 is the general vehicle speed sensor code from the engine computer. On vehicles where the output sensor is the vehicle speed sensor, both can set from the same failed part. Fix the sensor or wiring, then clear both. ### Why does my speedometer stop working with P0720? On many vehicles, especially trucks and rear-wheel-drive models, the output speed sensor also feeds the speedometer. When its signal drops out, the needle can bounce or fall to zero. Vehicles that use wheel speed sensors for the speedometer may show only shifting problems with P0720. ### How much does it cost to fix P0720? Most P0720 repairs cost $100 to $400 at an independent shop. Wiring or connector repairs run about $100 to $350, and replacing the output speed sensor usually costs $150 to $400. If heavy metal debris turns up and the fluid needs servicing too, the total can reach about $750. ### Where is the output speed sensor located? It usually sits near the rear of the transmission, on the extension housing or case, or on the transfer case on some four-wheel-drive vehicles. On front-wheel-drive cars it is often near the differential side of the transaxle. Service information for your transmission gives the exact spot. ### Can I replace the output speed sensor myself? Often yes, if you can reach it from under the vehicle with the car safely on ramps or jack stands. It is usually held by one bolt and sealed with an O-ring. Clean around it before removal, check the tip for metal debris, and top up any fluid lost. ### Can a bad output speed sensor cause harsh shifting? Yes, the transmission computer uses output speed to decide when to shift and how firmly. A wrong or missing signal can cause early or late shifts, firm engagement, or limp mode. Shifting usually returns to normal once the signal is fixed and any adaptive values settle or are relearned. ### Why does P0720 show up with ABS or traction control lights? Many vehicles share vehicle speed between modules over the network, and the ABS module compares wheel speeds with the transmission's speed signal. When the output sensor fails, other modules may flag a speed mismatch and turn on their own lights. Fixing the output sensor often clears them all. ### Can low transmission fluid cause P0720? Not usually directly, because the sensor reads a toothed ring, not the fluid. Low or very dirty fluid can cause other shift codes at the same time, though, and leaking fluid can soak the connector. Check the level and condition while the sensor is being diagnosed. ### Will cleaning the output speed sensor fix P0720? Sometimes, if a layer of metal debris on the magnetic tip was weakening the signal. Cleaning is free to try while the sensor is out. If the sensor has failed internally or the wiring is damaged, cleaning will not help, and heavy shavings mean the transmission needs a closer look. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) - [EPA: On-Board Diagnostics (OBD)](https://www.epa.gov/state-and-local-transportation/vehicle-emissions-board-diagnostics-obd) ## Other transmission codes - [P0700 Transmission Control System (MIL Request)](https://diagxcar.com/codes/p0700) - [P0705 Transmission Range Sensor "A" Circuit (PRNDL Input)](https://diagxcar.com/codes/p0705) - [P0715 Input/Turbine Speed Sensor "A" Circuit](https://diagxcar.com/codes/p0715) - [P0717 Input/Turbine Speed Sensor "A" Circuit No Signal](https://diagxcar.com/codes/p0717) - [P0730 Incorrect Gear Ratio](https://diagxcar.com/codes/p0730) - [P0731 Gear 1 Incorrect Ratio](https://diagxcar.com/codes/p0731) - [P0732 Gear 2 Incorrect Ratio](https://diagxcar.com/codes/p0732) - [P0740 Torque Converter Clutch Solenoid Circuit/Open](https://diagxcar.com/codes/p0740) - [P0741 Torque Converter Clutch Solenoid Circuit Performance/Stuck Off](https://diagxcar.com/codes/p0741) - [P0750 Shift Solenoid "A"](https://diagxcar.com/codes/p0750) ## Symptoms - [Why does my car jerk when I accelerate?](https://diagxcar.com/symptoms/car-jerks-when-accelerating) ## Repair costs - [Transmission fluid change cost](https://diagxcar.com/cost/transmission-fluid-change): $120-$350 - [Transmission replacement cost](https://diagxcar.com/cost/transmission-replacement) --- Source page: https://diagxcar.com/codes/p0720 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.