P0720 Code: Output Speed Sensor Circuit
Electrical fault in the output shaft speed signal – shift timing and sometimes the speedometer suffer.
At a glance
Severity: Moderate
- Meaning
- Output Speed Sensor Circuit
- System
- Transmission · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $60–$2,400
- DIY difficulty
- Moderate
The output speed sensor (OSS) reads the transmission output shaft, often by counting the teeth of the parking gear or a tone ring near the rear of the case or the final drive. The module uses it as its main measure of road speed: it decides when to shift, checks gear ratios against input speed, and on many trucks and older vehicles the same signal also drives the speedometer, cruise control and odometer. P0720 is the general circuit code – the module has detected an open, a short or a supply fault in the sensor circuit. Because the sensor sits low on the transmission, often right behind the front wheels or near the driveshaft, road spray, heat and debris are frequent contributors.
Can I keep driving? Drive with caution: the transmission may shift at the wrong time, hold a low gear or go into limp mode, and your speedometer may be unreliable. Keep an eye on your speed by traffic or a phone GPS and avoid highway driving until it's fixed.
How to read P0720
- P Powertrain
- 0 Generic (SAE)
- 7 Transmission
- 20 Specific fault
Symptoms
- Upshifts too early or too late, or no upshift out of low gears
- Speedometer dead, jumpy or reading low (where it uses this sensor)
- Cruise control won't engage or drops out
- Harsh downshift when coming to a stop
- ABS or traction light on some models that share the signal
- Check engine light, often with P0700 and a vehicle speed code
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Failed output speed sensor
- Wiring or connector damaged by road debris, heat or corrosion
- Metal debris on the magnetic tip or sensor partly unseated
- Supply voltage or ground missing to a Hall-type sensor
- Sensor integrated in conductor plate, mechatronic or transfer case failed
- Transmission module fault
Diagnosis step by step
Compare output speed with wheel speeds
On a road test, display output shaft speed (or transmission vehicle speed) next to the ABS wheel speeds. At a steady 30 mph they should agree within about 1–2 mph; a transmission reading of zero, jumping or missing while the wheels read normally isolates the output sensor circuit.
Tools: OBD-II scanner
Find and inspect the sensor
On rear-wheel-drive vehicles it is usually on the tail or extension housing; on front-wheel drive near the differential; on some 4x4s on the transfer case. Look for a cracked body, missing clip, burnt insulation near the exhaust or a connector packed with mud.
Tools: Flashlight
Measure the sensor
For a two-wire magnetic sensor, check resistance against spec (often several hundred to a couple of thousand ohms) and for any short to case ground. For a Hall sensor, verify supply and ground at the harness with the key on.
Tools: Multimeter
Check the tip and seating
Remove the sensor, clean any metallic fuzz from the magnet and inspect the O-ring. Reinstall fully seated and torque the bolt – a sensor that sits out even slightly can give a weak or missing signal.
Tools: Screwdriver, Torque wrench, Towels & shallow pan
Verify after repair
Clear the codes and road-test through all gears. Speedometer, shift points and cruise control should return to normal, and output speed should stay steady with no dropouts on the graph.
Tools: OBD-II scanner
Where the parts are
- 1Battery
- 2Alternator
- 3Engine computer (ECM)
- 4CAN bus
- 5Transmission
- 6Wheel speed sensor
- 7High-voltage battery
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Clean and repair sensor connector | Yes | $60–$180 |
| Repair heat- or debris-damaged wiring | No | $120–$300 |
| Replace external output speed sensor | Yes | $150–$350 |
| Replace internal sensor, conductor plate or mechatronic | No | $800–$2,400 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Honda
Honda service information calls the output sensor the countershaft speed sensor (and the input sensor the mainshaft speed sensor). On many Honda automatics both are external and bolted into the case, so a failed sensor is a relatively simple replacement.
Field data
| Ford | 98 | ||
|---|---|---|---|
| Nissan | 5 | 370z Roadster, Quest, Sentra | |
| Mazda | 3 | Tribute |
Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.
Emissions / smog test impact
Will fail
P0720 turns on the check engine light, so the car fails an OBD-based emissions or smog test. A dead speedometer can also be a safety-inspection issue in states that check it.
Frequently asked questions
Why did my speedometer stop working with P0720?
On many trucks and older cars, the transmission output sensor is the vehicle speed source for the speedometer. Newer vehicles often calculate speed from the ABS wheel sensors, so their speedometer may keep working while the transmission still loses its signal.
What's the difference between the input and output speed sensor?
The input sensor measures speed entering the transmission from the torque converter; the output sensor measures speed leaving it toward the wheels. The module compares the two to know which gear is really engaged.
Can I drive with P0720?
Short distances at moderate speed, yes, but shifts may be wrong and the speedometer unreliable. Avoid towing and highways – a transmission that holds a low gear at speed overheats quickly.
Is the output speed sensor the same as the vehicle speed sensor?
On some vehicles it is literally the same part; on others the vehicle speed comes from the ABS system and the output sensor is used only by the transmission. The service information for your model tells you which applies.