How do I fix error code P0720?
P0720 indicates a fault in the Output Speed Sensor circuit, typically the vehicle speed sensor (VSS) or its wiring. The usual remedy is to locate the faulty sensor or damaged wiring, replace or repair it, and then clear codes and verify with a road test.
What P0720 Means
P0720 is a generic powertrain fault code signaling that the transmission’s speed signal isn’t being read correctly by the engine control module. Without a reliable speed signal, the PCM/TCM can mishandle shift timing, idle control, and cruise control. The exact symptoms vary by vehicle and transmission type.
Common symptoms
These signs often accompany P0720, though not every vehicle will show all of them:
- Erratic or inaccurate speedometer readings
- Cruise control failures or intermittent operation
- Harsh, delayed, or unexpected transmission shifts
- Check Engine Light (MIL) illuminated with code P0720
Keep in mind that some cars may not display obvious symptoms yet still set the code during a diagnostic scan.
Diagnosis and Troubleshooting
Approaching P0720 requires a careful sequence of checks to confirm the fault source before replacing parts.
Outlined steps help technicians verify the problem and avoid unnecessary repairs.
- Use an OBD-II scanner to confirm P0720 and look for related codes (for example, codes pointing to the sensor, wiring, or PCM).
- Check live data for the VSS signal while driving or performing a controlled test to see if the signal is stable or intermittent.
- Inspect the VSS sensor and its wiring harness for damage, fraying, corrosion, or loose connectors near the transmission.
- Test the VSS sensor’s electrical behavior (resistance/voltage) according to the vehicle’s service manual. Look for open circuits or abnormal readings.
- Inspect the reluctor ring/tone wheel to ensure there are no damaged teeth or misalignment that could interrupt the signal.
- Check for shorts to ground or to power in the VSS circuit with a multimeter. Repair any damaged wiring or compromised connectors.
- Clear the codes and perform a road test to confirm the issue does not recur and the speed signal remains consistent.
After these checks, you’ll typically narrow the root cause to a faulty sensor, wiring issue, or PCM/TCM fault.
Common Causes
The following are the most frequent culprits behind P0720:
- Faulty vehicle speed sensor (VSS) or Output Speed Sensor (OSS)
- Damaged, frayed, or corroded wiring or connectors in the VSS circuit
- Ground or power supply problems affecting the VSS circuit
- Damaged reluctor ring or tone wheel causing inconsistent signal
- PCM/TCM faults or software issues in some vehicle configurations
In modern transmissions, the VSS may be integrated with other control modules. If the fault persists, this can require more advanced diagnostics, including module reprogramming or replacement.
Repair Steps
Once the faulty component or issue is identified, follow these practical repair steps to restore proper speed sensing:
- Replace a confirmed faulty VSS/OSS sensor with a proper unit for the specific vehicle.
- Repair or replace damaged wiring or connectors in the VSS circuit; ensure clean grounds and secure harness routing.
- Re-seat or replace the sensor connector to ensure proper contact and locking.
- Repair or replace a damaged reluctor ring or tone wheel and verify proper spacing from the sensor.
- Clear the codes with a diagnostic tool and perform a cautious road test to confirm the fix.
- If the code returns, consider deeper diagnostics of the PCM/TCM and possible software updates or replacement by a professional.
After repairs, re-test the vehicle’s speed signal, transmission shifting behavior, and cruise control performance across multiple driving conditions to confirm the issue is resolved.
When to Seek Professional Help
If you lack diagnostic tools or hands-on experience with transmission sensors and wiring, or if the code recurs after initial repairs, a certified technician can perform advanced tests. These may include live-data monitoring, resistance checks, wiring harness diagnostics, and potential PCM reflash or replacement.
Summary
P0720 signals a fault in the Output Speed Sensor circuit, most commonly involve the vehicle speed sensor, its wiring, or the associated transmission electronics. A disciplined approach—diagnosing with live data, inspecting wiring and connectors, testing the sensor, and performing targeted repairs—usually resolves the issue. Because vehicle designs vary, always consult the specific service manual for exact test procedures, resistance ranges, and torque specifications. If in doubt, professional diagnosis is recommended to avoid unintended transmission damage.
What is the symptoms of P0720 output speed sensor?
Symptoms of a P0720 code include the check engine light turning on, a non-functional or erratic speedometer, and transmission issues like delayed or harsh shifting, or even stalling. Other symptoms can include cruise control failure, decreased fuel economy, and incorrect ABS or traction control operation.
Common symptoms
- Illuminated Check Engine Light: This is often the first indicator of a problem.
- Speedometer and Odometer Issues: The speedometer may not work at all, show incorrect readings, or the odometer may be affected.
- Transmission Performance Problems:
- Rough or delayed shifting: The transmission may not shift gears smoothly or at the right time.
- Harsh shifts: Gears may engage with a sudden jolt.
- Stalling: The vehicle may stall when coming to a stop.
- Gear limitations: Some vehicles may not shift into higher gears.
- Decreased Fuel Economy: The engine may work less efficiently, leading to lower gas mileage.
- Cruise Control Malfunction: The cruise control system may not engage or may disengage unexpectedly.
- ABS and Traction Control Issues: The vehicle's anti-lock brake and traction control systems may operate improperly because they rely on speed sensor data.
Where is the output shaft speed sensor circuit located?
The output shaft speed sensor is located in the transmission assembly beneath the valve body. You will need to drain the fluid, remove the pan, and take out the valve body assembly. After that, you will be able to access the speed sensor for replacement.
How much does it cost to fix a P0720?
In most cases, the error code can be remedied by replacing the output shaft speed sensor or by servicing the transmission fluid. RepairPal estimates replacing an output shaft speed sensor costs between $290 and $340, on average. The cost of replacing transmission fluid comes in at around $200.
Can I drive with a P0720 code?
The P0720 code doesn't usually prevent a vehicle from driving altogether, but it can cause serious driveability issues. However, the effects of this code do get worse the longer it is left unaddressed. This means that you risk further damage to your engine and transmission by not inspecting the issue.
