The P0720 code is a generic powertrain code related to transmission issues. It specifically indicates a malfunction in the output speed sensor circuit. This sensor, also known as the Vehicle Speed Sensor (VSS) in some vehicles, plays a crucial role in providing speed data to the Powertrain Control Module (PCM). When the PCM detects an issue with this sensor’s signal, it triggers the P0720 code.
| P0720 Code Meaning | P0720 Code Common Causes |
|---|---|
| Output Speed Sensor Circuit Malfunction | Faulty output shaft speed sensor |
| Erratic or insufficient input from OSS | Damaged wiring or connectors |
| PCM detects discrepancy in speed readings | Contaminated transmission fluid |
| Transmission-related issue affecting speed sensing | Malfunctioning PCM (rare) |
Symptoms of P0720 Code
When your vehicle’s computer detects the P0720 code, you may experience various symptoms that can affect your driving experience. It’s essential to be aware of these signs to address the issue promptly:
- Illuminated Check Engine Light
- Erratic or non-functioning speedometer
- Harsh or delayed gear shifts
- Cruise control malfunction
- Transmission entering “limp mode”
- Stalling when coming to a stop
- Inaccurate odometer readings
These symptoms can vary depending on the vehicle make and model, as well as the severity of the sensor malfunction. Some drivers may notice multiple symptoms, while others might only see the Check Engine Light without any apparent drivability issues.
Technical Explanation of P0720 Code
The P0720 code is set when the PCM detects an issue with the output speed sensor circuit. This sensor, typically located on the transmission’s output shaft or within the differential, uses a magnetic pickup to generate a signal based on the rotation of a toothed wheel. As the transmission output shaft rotates, the sensor produces a frequency signal proportional to the vehicle’s speed.
The PCM uses this data for various functions, including:
- Determining appropriate gear shifts
- Controlling the speedometer
- Managing the cruise control system
- Calculating vehicle speed for other control modules
When the PCM detects that the signal from the output speed sensor is erratic, missing, or doesn’t correlate with other sensor inputs (such as the engine speed and input shaft speed), it will set the P0720 code. This can happen due to electrical issues in the sensor circuit, a faulty sensor, or problems with the transmission itself affecting the sensor’s ability to read the output shaft speed accurately.
Step-by-Step Diagnosis of P0720 Code
Diagnosing the P0720 code requires a systematic approach to identify the root cause of the problem. Follow these steps for an accurate diagnosis:
- Verify the code: Use an OBD-II scanner to confirm the P0720 code and check for any additional related codes.
- Check for Technical Service Bulletins (TSBs): Research if there are any known issues or recalls related to the output speed sensor for your specific vehicle make and model.
- Inspect the wiring and connectors: Examine the wiring harness and connectors associated with the output speed sensor for signs of damage, corrosion, or loose connections.
- Check transmission fluid: Verify the transmission fluid level and condition. Low or contaminated fluid can affect sensor readings.
- Test the output speed sensor: Using a multimeter, check the resistance of the sensor and compare it to the manufacturer’s specifications.
- Analyze sensor signal: With a digital oscilloscope, observe the output speed sensor’s signal pattern while the vehicle is in motion.
- Inspect the reluctor ring: If accessible, check the condition of the reluctor ring (toothed wheel) that the sensor reads.
- Perform a road test: Drive the vehicle to see if the symptoms are reproducible and to gather more data from the scanner.
- Check PCM grounds: Ensure all PCM ground connections are clean and secure.
- Consult vehicle-specific diagnostic procedures: Follow any additional steps outlined in your vehicle’s service manual.
Solution Methods for P0720 Code
After diagnosing the issue, you can proceed with the appropriate repair method. Here are common solutions for the P0720 code:
1. Repair or Replace Wiring and Connectors
If you’ve found damaged wiring or corroded connectors:
- Clean corroded terminals with electrical contact cleaner
- Repair any broken or frayed wires using proper splicing techniques
- Replace severely damaged sections of the wiring harness
- Ensure all connections are secure and protected from moisture
2. Replace the Output Speed Sensor
If the sensor itself is faulty:
- Locate the sensor on your transmission (consult your vehicle’s manual for exact location)
- Remove any components obstructing access to the sensor
- Unplug the electrical connector and unscrew the sensor
- Install the new sensor, ensuring it’s seated properly
- Reconnect the electrical connector and any removed components
3. Change Transmission Fluid
For contaminated or low transmission fluid:
- Place a drain pan under the transmission
- Remove the drain plug and allow the old fluid to drain completely
- Replace the drain plug and refill with the correct type and amount of transmission fluid
- Check for leaks and ensure the fluid level is correct
4. Repair or Replace Reluctor Ring
If the reluctor ring is damaged:
- This typically requires transmission disassembly and should be performed by a professional
- The reluctor ring may need to be replaced or resurfaced depending on the extent of damage
5. PCM Reprogramming or Replacement
In rare cases where the PCM is at fault:
- Check for available software updates for your vehicle’s PCM
- If reprogramming doesn’t resolve the issue, PCM replacement may be necessary
- This should be done by a professional as it requires specialized equipment and knowledge
Cost Estimates for P0720 Code Repairs
The cost to repair issues related to the P0720 code can vary widely depending on the root cause and your vehicle’s make and model. Here are some estimated ranges:
- Output Speed Sensor Replacement: $150 – $400
- Wiring Repair: $100 – $300
- Transmission Fluid Change: $100 – $250
- Reluctor Ring Replacement: $500 – $1500 (due to labor-intensive nature)
- PCM Reprogramming: $50 – $200
- PCM Replacement: $500 – $2000
These estimates include parts and labor but can vary based on your location and the specific repair shop. Always get multiple quotes for major repairs.
Warnings and Recommendations
Important safety considerations when dealing with the P0720 code:
- Never ignore a Check Engine Light, as it could indicate a serious issue.
- If you experience severe drivability issues, stop driving the vehicle to prevent further damage.
- Always disconnect the battery before working on electrical components.
- Use caution when working around hot engine components.
- Consult a professional if you’re unsure about any repair procedures.
- Use only manufacturer-recommended replacement parts and fluids.
- After repairs, clear the code and perform a thorough test drive to ensure the issue is resolved.
Preventing Future P0720 Code Issues
To minimize the risk of encountering the P0720 code in the future:
- Adhere to your vehicle’s recommended maintenance schedule
- Regularly check and maintain proper transmission fluid levels
- Address any transmission-related issues promptly
- Avoid driving through deep water, which can damage electrical components
- Keep your vehicle’s undercarriage clean to prevent corrosion of sensors and wiring
- Consider using dielectric grease on electrical connections to prevent corrosion
By following these preventive measures, you can help ensure the longevity and proper function of your vehicle’s transmission and related components.
Frequently Asked Questions About P0720
- Can I drive my car with a P0720 code?
While sometimes possible, it’s not recommended. The code can indicate issues that may lead to further transmission damage or unsafe driving conditions. - How urgent is it to fix a P0720 code?
It’s important to address this code promptly. Ignoring it can lead to more severe transmission problems and potentially dangerous driving situations. - Will a P0720 code clear itself?
The code may clear temporarily if the issue resolves, but it will likely return if the underlying problem isn’t fixed. - Can a bad battery cause a P0720 code?
While unlikely, a weak battery can cause various electrical issues that might indirectly trigger this code. It’s best to rule out battery problems during diagnosis. - Is the P0720 code related to ABS problems?
The output speed sensor data is often used by the ABS system, so a P0720 code can sometimes be accompanied by ABS-related issues or codes. - How long does it take to fix a P0720 code?
Repair time can vary from 1-2 hours for simple sensor replacement to several days if major transmission work is required. - Can I replace the output speed sensor myself?
In many vehicles, this is a DIY-friendly repair. However, the sensor’s location and accessibility can vary, so consult your vehicle’s manual first. - Will a P0720 code affect my fuel economy?
It can, especially if the transmission is not shifting properly as a result of the faulty speed sensor data.
In conclusion, the P0720 code, while potentially serious, is often resolvable with proper diagnosis and repair. Whether you’re a DIY enthusiast or prefer professional service, addressing this issue promptly can save you from more extensive and costly repairs down the road. Always prioritize safety and consult with a certified mechanic if you’re unsure about any aspect of the diagnosis or repair process.