Acura MDX P0720 Trouble Code (2008-2020): Output Speed Sensor Causes and Fixes

What's Unique About the 2008-2020 Acura MDX

The 2008-2020 MDX spans two generations with three different automatic transmissions, which is key to understanding this code. Second generation models (2008-2013) and early third-gen models (2014-2015) use a Honda-built 5-speed or 6-speed automatic where the output speed sensor is a common, accessible, and well-documented failure point. However, later third-gen models (2016-2020) use a ZF-sourced 9-speed automatic (ZF 9HP series). On these 9-speed models, the speed sensors are integrated into the valve body inside the transmission, making diagnosis and replacement a much more involved and expensive professional job.

Generation note: This guide covers the second (2008-2013) and third (2014-2020) MDX generations. * 2008-2015 (5-speed & 6-speed A/T): The most common failure is an external, easily replaceable output speed sensor. This is a well-documented issue and a feasible DIY repair. The sensor is located on the exterior of the transmission housing. * 2016-2020 (9-speed A/T): These models use a ZF 9-speed transmission (ZF 9HP). The speed sensors are located internally on the valve body. A P0720 code on these models is a more serious issue requiring professional teardown of the transmission. Software updates and TCM issues are also common on these models, as noted in TSB 20-015 which addresses harsh shifting.

Symptoms You May Notice

• Harsh, erratic, or delayed gear shifts.
• Flashing 'D' (Drive) indicator light on the dashboard.
• Inaccurate or completely non-functional speedometer.
• Check Engine Light is illuminated.
• Cruise control will not engage or stops working.
• Vehicle may get stuck in one gear (limp mode).
• In some cases, the vehicle may not shift into Park unless turned off first.
• Stalling when coming to a stop.

Most Likely Causes

1. Failed Output/Countershaft Speed Sensor 🔴 High Probability This is a common electronic failure point on many Honda/Acura transmissions from the 2008-2015 era due to heat cycles and vibration. It is a widely shared part across Honda and Acura models.
   How to confirm: After confirming no wiring issues, test the sensor's resistance with a multimeter. Compare the reading to the factory specification. An out-of-spec reading confirms a bad sensor. Alternatively, given the high failure rate and low part cost, many owners and shops replace the sensor as a primary diagnostic step.
   Typical fix: Replace the output speed sensor. On 2008-2015 models, this sensor is external and held by a single 10mm bolt.
   Est. part cost: $40-$90
2. Damaged Wiring or Connector 🟡 Medium Probability The wiring harness is located underneath the vehicle and is exposed to road debris, moisture, and heat, which can lead to corrosion or physical damage over time. The connector itself can also fail.
   How to confirm: Visually inspect the wiring harness and connector leading to the output speed sensor for any signs of fraying, breaks, or corrosion. Perform a continuity test on the wires between the sensor connector and the PCM.
   Typical fix: Repair the damaged section of wire or replace the connector pigtail.
   Est. part cost: $10-$30
3. Low or Dirty Transmission Fluid ⚪ Low Probability → Shop Transmission Assembly
   How to confirm: Check the transmission fluid level and condition according to the owner's manual procedure. Fluid should be at the correct level, red in color, and not smell burnt. Very dark or debris-filled fluid suggests larger internal problems.
   Typical fix: Perform a transmission fluid drain-and-fill using the correct Acura ATF DW-1 fluid. If the fluid is very dark or contains metal particles, a larger internal transmission problem may be present, potentially related to torque converter issues mentioned in TSBs.
   Est. part cost: $50-$100

Rare But Worth Checking

• Faulty Powertrain Control Module (PCM) or Transmission Control Module (TCM): → Shop Engine Control Module (ECM) This is the least likely cause. All other possibilities, especially the sensor and its wiring, should be exhaustively ruled out before considering PCM/TCM replacement.
• Internal Transmission Fault (2016-2020 Models): → Shop Transmission Assembly On the ZF 9-speed transmissions, a P0720 code could indicate a problem with the internally-mounted sensor, the valve body it's attached to, or other internal transmission hardware. This was the subject of a lawsuit alleging defects in these transmissions.

Diagnosis Steps

1. Read the trouble codes with an OBD-II scanner to confirm P0720 and check for any other related codes.
2. Check the level and condition of the automatic transmission fluid. Ensure it is clean, at the proper level, and does not smell burnt.
3. Inspect the wiring harness and electrical connector at the output speed sensor for visible damage, corrosion, or loose connections.
4. On 2008-2015 models, locate the output sensor on the exterior of the transmission. Access is typically from underneath after removing a splash shield, though some owners access it from the top by removing the airbox.
5. If the wiring appears intact, test the sensor. Disconnect it and measure the internal resistance with a multimeter. Compare this value to the manufacturer's specification. An open circuit or incorrect resistance indicates a failed sensor.
6. If the sensor tests good, the next step is to check for continuity and shorts in the wiring between the sensor connector and the PCM.
7. If the sensor and wiring are confirmed to be good, the issue may lie with the Powertrain Control Module (PCM), though this is rare.
8. For 2016-2020 models, diagnosis will likely require a professional scan tool to monitor sensor data and will lead to internal transmission inspection if the sensor is suspected.

Parts You'll Likely Need

• Automatic Transmission Output Speed Sensor (OEM #28810-RWE-003) — This sensor is the most common point of failure for the P0720 code on 2008-2015 models. It is an electronic component that wears out over time. It is a widely shared part across Honda and Acura models.
  Trusted brands: Acura (OEM), NTK, Standard Motor Products (SMP), Beck/Arnley, Dorman
  OEM price range: $110-$160
  Aftermarket price range: $40-$90
• Acura ATF DW-1 Transmission Fluid (OEM #08200-9008A) — If the transmission fluid is found to be low or dirty during diagnosis, it must be replaced. It is critical to use the specific fluid recommended by Honda/Acura. This is also required for TSB procedures related to transmission judder.
  Trusted brands: Acura (OEM)
  OEM price range: $10-$15 per quart
  Aftermarket price range: N/A

Related Codes That Often Appear With This One

• P0722 — This code means 'Output Speed Sensor Circuit No Signal,' which is a more specific version of the general P0720 fault. They often appear together or point to the same root cause.
• P0721 — This code means 'Output Speed Sensor Circuit Range/Performance,' indicating the sensor's signal is erratic or irrational. It is also directly related to a failing sensor or wiring.

Technical Service Bulletins (TSBs) & Recalls

• Acura TSB 20-015: Addresses intermittent harsh or jerky upshifts on 2016-2020 MDX models with the 9-speed transmission. The fix is a TCM software update. While not directly for P0720, it highlights the known software issues with the ZF 9-speed transmission.
• Acura TSB 17-040 / 15-086: Pertains to a judder felt while driving under light acceleration on various Honda/Acura models, including the MDX. The fix involves a software update and potentially a torque converter replacement. Degraded fluid from this issue could theoretically contribute to other transmission problems.

Platform-Specific Known Issues

• Uncertainty for 2016-2020 Models: The ZF 9-speed transmission used in these model years has a different design. The output speed sensor is internal to the transmission and integrated with the valve body, not an easily accessible external part. A P0720 on these vehicles is a sign of a more significant internal issue requiring professional diagnosis and repair. These transmissions were also subject to a lawsuit regarding shifting behavior and potential defects.
• Owner Experience (2008-2015): A YouTube video by 'modsforever' shows a repair on a similar Acura TL transmission where the car would not shift into park and the speedometer failed. The fix was replacing the external output speed sensor, which is accessed from the top of the engine bay after removing the airbox.

Mechanic-Grade Diagnostic Values

• Reference Voltage at Sensor Connector — expected: Approximately 5.0 volts with key on, engine off.. Failure: Significantly lower or no voltage suggests a wiring or PCM issue, not a sensor failure.
• Sensor Internal Pins — expected: The sensor has three pins: Ground, VCC (power), and Out (signal).. Failure: An open or short between these pins when tested with a multimeter indicates a failed sensor.

Scan Tool Commands That Help

• Honda HDS (or equivalent professional scanner): Live Data Monitoring for 'Output Shaft Speed' or 'VSS' — This is the most effective way to diagnose an intermittent failure. While driving, a technician can watch the sensor's data stream. If the reading drops to zero, becomes erratic, or doesn't increase smoothly with vehicle speed, it confirms a fault in the sensor or its circuit.
• Honda HDS (or equivalent professional scanner): Clear TCM/PCM Codes — After replacing the sensor or repairing the wiring, the stored P0720 code must be cleared from the transmission and powertrain control modules. A standard OBD-II reader may not clear all module-specific codes, so a more advanced tool is recommended.

Wiring & Ground Locations

• G301 — Located on the left side of the engine compartment, often on or near the transmission housing.. This is a primary ground point for the transmission and its associated electronics. A corroded or loose G301 ground can cause a variety of erratic electrical issues, including intermittent sensor signals that could trigger a P0720 code.
• Transmission Ground Cable (PN 32601-STX-A01) — A specific ground strap that connects the transmission case directly to the chassis.. This cable ensures the transmission has a solid ground path. If this strap is broken, frayed, or its connection points are corroded, it can lead to floating grounds and unpredictable behavior from sensors like the OSS.
• PCM Connector Pins — At the Powertrain Control Module (PCM), specific pins receive the signal from the output speed sensor.. For a definitive circuit diagnosis, a technician would test for continuity and voltage directly at the PCM pins corresponding to the OSS. This confirms whether the wiring is intact all the way from the sensor to the computer.

Real Owner Repair Stories

• YouTube user 'modsforever' (Acura (model similar to MDX, demonstrating a common Honda/Acura repair)) — Vehicle would not shift into Park unless it was turned off first, and the speedometer stopped working. The 'D' light was flashing.
  ✅ What actually fixed it The problem was resolved by replacing the external Automatic Transmission Output Speed Sensor. The repair was done from the top of the engine bay by removing the airbox for access.

OEM Part Supersession History

• 28810-RWE-003 → N/A — This part number appears to be stable for the affected 2008-2015 model years.
  Heads up: This part is specific to the 5-speed and 6-speed automatic transmissions used through 2015. It is NOT compatible with the 2016-2020 models equipped with the ZF 9-speed transmission, as those sensors are internal.

Model Year Variations Within This Range

• 2008-2015: These models use a Honda 5-speed or 6-speed automatic transmission with an external, easily replaceable output speed sensor (PN 28810-RWE-003). The repair is straightforward and a common DIY task.
• 2016-2020: These models use a ZF 9-speed (9HP) automatic transmission. The speed sensors are internal to the transmission and integrated with the valve body/TCM. A P0720 code on these vehicles indicates a much more serious internal fault requiring professional disassembly and is not a simple sensor swap.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Excessive Oil Consumption (VCM Engines) 🔴 High — Common on 3.7L (2010-2013) and 3.5L VCM-equipped engines. Can occur at any mileage but often noted after 60,000 miles. (Ref: Subject of a class-action lawsuit and warranty extension (e.g., TSB 19-006).)
• Torque Converter Judder/Shudder 🟠 Medium — Common on 2012-2015 models, typically felt between 20-60 mph under light acceleration. (Ref: Acura TSB 16-044, 17-040. Fix involves software updates, fluid flushes, and potential torque converter replacement.)
• ZF 9-Speed Transmission Harsh Shifting/Lurching 🟠 Medium → Shop Transmission Assembly — Affects 2016-2020 models. Can be present from low mileage. Subject of a class-action lawsuit. (Ref: Acura TSB 20-015 provides a software update to address harsh upshifts.)
• Parasitic Battery Drain from HFL/Bluetooth Module 🟡 Low — Common on 2nd generation (2007-2013) models. The module fails to shut down, draining the battery overnight. (Ref: No TSB, common knowledge in owner forums. Fix is to disconnect or replace the HFL module.)
• Active Damper System (ADS) Leaks 🟠 Medium — Affects 2nd generation (2007-2013) models equipped with the Sport Package, particularly in cold climates. (Ref: Acura TSB 16-022 describes the issue and replacement procedure.)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this repair, a used part is almost never recommended for the sensor itself. However, if the wiring connector (pigtail) is damaged, sourcing a used pigtail from a junkyard is an excellent and cost-effective option, as it provides a factory-quality connector to splice into your harness.

Donor-vehicle mileage cap: roughly under 100000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• For a wiring pigtail, ensure the plastic is not brittle or cracked.
• Check that the connector's locking tab is intact.
• Inspect the pins inside the connector for any signs of corrosion (green or white powder).
• Verify the donor vehicle did not have a front-end collision that could have stressed the harness.

OEM-only on this vehicle (don't cheap out):

• Acura ATF DW-1 Transmission Fluid. Using non-specified fluid can cause shifting problems and long-term damage.

Aftermarket brands forum-validated for this vehicle:

• NTK
• Standard Motor Products (SMP)
• Beck/Arnley

Brands owners have reported issues with on this vehicle:

• Unbranded, no-name sensors from online marketplaces are frequently cited as having poor quality control and may fail prematurely or be dead-on-arrival.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• P0721 — Often triggered alongside P0720 as it relates to output speed sensor range/performance issues.
• P0722 — A companion code indicating 'No Signal' from the same output speed sensor circuit.
• P0741 — Related to torque converter performance; may appear if degraded fluid or internal issues mentioned in TSB 17-040 are present.

Frequently Asked Questions