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P0720
Difficulty: AdvancedTime: 4-8 hoursUpdated: March 10, 2025

title: "2009 Mazda Mazda6 P0720 — Output Speed Sensor Circuit Malfunction Diagnosis & Fix", description: "Expert diagnosis and repair guide for the P0720 trouble code on your 2009 Mazda Mazda6. Learn common symptoms, diagnostic steps, and fix options.", make: "mazda", model: "mazda6", year: 2009, slug: "P0720-output-speed-sensor", dtcCode: "P0720", publishedAt: "2024-11-01", updatedAt: "2025-03-10", difficulty: "advanced", estimatedTime: "4-8 hours", tags: ["obd2", "dtc", "mazda", "P0720", "transmission", "mazda6"], }

P0720: Output Speed Sensor Circuit Malfunction

The P0720 trouble code on your 2009 Mazda Mazda6 indicates a problem with the output speed sensor circuit malfunction. This diagnostic trouble code is one of many OBD-II codes that your vehicle's on-board diagnostic system uses to alert you to potential issues requiring attention.

What Does the P0720 Code Mean?

When your Mazda's Powertrain Control Module (PCM) detects a malfunction in the output speed sensor circuit malfunction, it stores the P0720 code and illuminates the check engine light. This system works in conjunction with Mazda's advanced SKYACTIV technology to monitor critical engine and transmission functions in real-time.

With its lightweight aluminum block and advanced valve timing control, the SKYACTIV-G engine delivers responsive performance while maintaining excellent fuel economy.

Your 2009 Mazda6 features advanced engineering designed to maximize both performance and efficiency. Understanding how this system relates to the P0720 code can help you diagnose the issue more effectively.

Common Symptoms of P0720

If your 2009 Mazda Mazda6 is experiencing the P0720 code, you may notice one or more of the following symptoms:

  • Delayed or harsh gear shifts, particularly when cold
  • Transmission slipping or failure to engage gears properly
  • Unusual noises during acceleration or deceleration

The check engine light will typically remain illuminated when this fault is active. In some cases, you may also notice:

  • Changes in engine performance or responsiveness
  • Unusual sounds coming from the engine bay
  • Shifting irregularities if the issue affects transmission functions
  • Reduced fuel efficiency compared to normal operation

Diagnostic Steps for P0720 on Mazda Mazda6

Proper diagnosis of the P0720 code requires a systematic approach. Here's how professional technicians typically handle this:

Step 1: Verify the Code

Using a compatible OBD-II scanner, confirm the presence of the P0720 code and check for any additional codes that may be stored. Note any pending or permanent codes as these can provide valuable diagnostic information.

Step 2: Visual Inspection

Check transmission fluid level and condition using the dipstick

Inspect all related wiring, connectors, and components for obvious signs of damage, corrosion, or wear. Pay particular attention to:

  • Wiring harness routing near heat sources
  • Connector seals and locking mechanisms
  • Signs of fluid leaks that could affect electrical components

Step 3: Component Testing

Inspect transmission wiring harness for damage or corrosion

Use appropriate testing equipment to verify proper operation of the affected component. This may include:

  • Multimeter testing for voltage, resistance, and continuity
  • Oscilloscope analysis for signal quality
  • Scan tool data monitoring for real-time values

Step 4: Pinpoint Testing

Perform a transmission control module relearn procedure if available

Narrow down the cause by testing specific circuits and components identified in earlier steps. Document all test results for reference during repair.

Step 5: Verify Repair

After completing repairs, clear the code and operate the vehicle under similar conditions to confirm the issue has been resolved. The check engine light should remain off and no codes should return.

Common Causes of P0720

The P0720 code in your 2009 Mazda Mazda6 can be caused by several factors:

  • Performing transmission fluid change using Mazda-specified fluid
  • Causes include replacing faulty shift solenoids individually or as a complete set
  • Causes include repairing or replacing damaged transmission wiring harness
  • In severe cases, complete transmission replacement or rebuild

Other potential causes include normal wear on high-mileage components, water intrusion into electrical connectors, and aftermarket modifications that alter factory wiring.

How to Fix P0720

Repair Options

Performing transmission fluid change using mazda-specified fluid: Professional repair may be required. Replacing faulty shift solenoids individually or as a complete set: Professional repair may be required. Repairing or replacing damaged transmission wiring harness: Professional repair may be required.

Parts to Consider

When addressing the P0720 code on your 2009 Mazda6, you may need:

  • OEM or equivalent replacement parts for your specific Mazda model
  • New gaskets or seals if leaks are present
  • Electrical connectors and terminals if corrosion is found
  • Specialized tools for testing and repair

Professional vs. DIY

While some P0720 issues can be resolved by experienced DIY mechanics, others require dealer-level diagnostic equipment and expertise. Consider the following:

  • DIY Suitable: Basic visual inspections, connector cleaning, and part replacement on accessible components
  • Professional Required: Module programming, transmission diagnostics, and complex electrical troubleshooting

Preventing P0720 Issues

Regular maintenance can help prevent the P0720 code from recurring:

  • Follow Mazda's recommended maintenance schedule for your Mazda6
  • Use only approved fluids and parts for your SKYACTIV engine
  • Address check engine lights promptly before they lead to more serious issues
  • Keep electrical connectors clean and protected from the elements

2009 Mazda Mazda6 Specific Information

Your 2009 Mazda6 incorporates several unique features that may affect how the P0720 code manifests:

Mazda's SKYACTIV-G technology represents a revolutionary approach to gasoline engine design, featuring ultra-high compression ratios of up to 14:1 for exceptional fuel efficiency and power output.

Mazda's G-Vectoring Control system adjusts engine torque during cornering to improve vehicle handling and reduce driver workload.

These systems work together through Mazda's i-ACTIV philosophy, which emphasizes the connection between driver, vehicle, and road conditions.

Conclusion

The P0720 code on your 2009 Mazda Mazda6 should not be ignored, but with proper diagnosis and repair, most issues can be resolved effectively. Whether you tackle this as a DIY project or seek professional assistance, understanding the cause and following a systematic diagnostic approach will lead to the best outcome.

Remember that proper repair now can prevent more costly issues down the road and help maintain your Mazda's legendary driving dynamics for years to come.