P1720 on 2010-2012 Hyundai Santa Fe: Why This Code is a Red Flag for Your Scanner

What's Unique About the 2010-2012 Hyundai Santa Fe

On this generation of Hyundai Santa Fe, like many other Hyundai models of the era, the transmission and ABS systems are highly integrated. A fault in one system can trigger warning lights in others (ABS, ESC, 4WD). The key issue is that generic scanners often fail to properly translate Hyundai's proprietary transmission codes, leading to the display of phantom codes like P1720. The actual problem could be as simple as an external ABS sensor or as complex as an internal transmission harness, making a proper diagnosis essential.

Symptoms You May Notice

• Check Engine Light is on
• ABS, Traction Control (ESC), and/or 4WD warning lights are on
• Transmission shifts harshly or erratically
• Transmission gets stuck in a single gear (often 3rd gear, known as 'limp mode')
• Inaccurate or non-functional speedometer
• Cruise control may be disabled

Most Likely Causes

1. Generic OBD-II Scanner Error 🔴 High Probability Hyundai uses manufacturer-specific codes that basic scanners cannot interpret correctly, often defaulting to a phantom P1720.
   How to confirm: Scan the vehicle with a professional, high-end scan tool that can read Hyundai-specific powertrain (P-codes), chassis (C-codes), and network (U-codes) faults.
   Typical fix: Identify the actual trouble codes with a proper scanner. The P1720 code will disappear, and the real codes (e.g., P0717, C1203, P2159) will be revealed.
   Est. part cost: $0
2. Failed ABS Wheel Speed Sensor (Underlying Cause) 🟡 Medium Probability → Shop ABS Wheel Speed Sensor These sensors are exposed to the elements and can fail from damage, corrosion, or internal faults, sending an erratic signal that confuses the vehicle's computer systems.
   How to confirm: A professional scan will likely show a chassis code like C1203 (Right Front Sensor Open or Short) or a powertrain code like P2159 (Rear Wheel Speed Sensor Circuit Range/Performance). Live data will show one wheel speed sensor reading zero or an erratic signal while the others work correctly.
   Typical fix: Replace the faulty ABS wheel speed sensor. 🎬 See this step-by-step ABS wheel speed sensor replacement Inspect the wiring and connector for damage first.
   Est. part cost: $50-$150
3. Failed Internal Transmission Wire Harness (Underlying Cause) 🟡 Medium Probability → Shop Transmission Assembly The harness, which includes the input/output speed sensors and temperature sensor, is located inside the transmission pan and degrades over time from heat and fluid exposure. This is a known issue on this family of Hyundai 6-speed automatic transmissions.
   How to confirm: A professional scan will reveal codes like P0717 (Input Speed Sensor), P0721/P0722 (Output Speed Sensor), or P0711 (Transmission Temp Sensor). A technician will confirm by seeing the sensor data drop out on the scan tool.
   Typical fix: Replace the internal transmission wire harness (OEM Part No. 46307-3B650). 🎬 Watch: How to replace the internal transmission harness This requires draining the transmission fluid, removing the oil pan, and removing the valve body to access the harness.
   Est. part cost: $70-$150

Diagnosis Steps

1. STOP. Do not proceed with any repairs based on the P1720 code alone.
2. Take the vehicle to a qualified technician or use a professional-grade scan tool capable of reading Hyundai-specific codes.
3. Record all codes from all modules (Engine, Transmission, ABS, 4WD).
4. If codes like C1203 or P2159 are present, inspect the corresponding ABS wheel speed sensor, its wiring, and connector for physical damage. Use the scan tool's live data to confirm which sensor is not reading.
5. If codes like P0717, P0721, P0722, or P0711 are present, the issue is likely the internal transmission wire harness. This is a complex repair best left to a professional.
6. If other codes are present, diagnose them according to the factory service manual.
7. After repair, clear all codes and perform a test drive to ensure the issue is resolved.

Parts You'll Likely Need

• ABS Wheel Speed Sensor (OEM #e.g., 95670-2B210 (Front Right)) — This is a common failure point that can trigger a cascade of speed-related fault codes that a generic scanner might misread as P1720.
  Trusted brands: Bosch, Delphi, Standard Motor Products (SMP), Hyundai (OEM)
  OEM price range: $100-$180
  Aftermarket price range: $40-$90
• Internal Transmission Wire Harness (OEM #46307-3B650) — This harness contains multiple sensors (input speed, output speed, temp) and is a known failure point inside the transmission due to heat and fluid exposure, causing codes that are often misread as P1720.
  Trusted brands: Hyundai (OEM)
  OEM price range: $70-$150
  Aftermarket price range: $50-$100

Related Codes That Often Appear With This One

• P0717, P0721, P0722 — These are the likely *real* codes for input/output speed sensor failures that a generic scanner misinterprets as P1720. They are part of the internal harness.
• C1203, P2159 — These are Hyundai-specific codes for a faulty wheel speed (ABS) sensor, which can also be misinterpreted or appear alongside the phantom P1720. A single faulty ABS sensor can disable multiple systems.
• P0711 — This code for the transmission fluid temperature sensor is often triggered along with speed sensor codes, as the sensor is part of the same internal harness assembly (46307-3B650).

Technical Service Bulletins (TSBs) & Recalls

• TSB 14-AT-013 / 20-AT-011H: These TSBs supersede earlier versions and specifically address DTCs P0717, P0721, and P0722 for the 2010-2012 Santa Fe (CM), instructing technicians to replace the internal harness rather than the entire transmission.

Platform-Specific Known Issues

• Owner Experience: P1720 leading to Internal Harness Replacement: A user on hyundai-forums.com with a 2011 Santa Fe reported their Check Engine, ESC, and AWD lights came on, and the transmission was stuck in 3rd gear. A generic scanner pulled P1720. After advice from the forum, they took it to a dealer who used a proper scanner and found codes P0717 and P0722. The dealer confirmed the internal transmission wiring harness had failed. The repair involved replacing the harness (part #46307-3B650), which resolved all symptoms.

Mechanic-Grade Diagnostic Values

• ABS Wheel Speed Sensor (Active Hall-Sensor Type) Current — expected: 7mA to 14mA. Failure: Current outside the 7-14mA range for more than 200ms will set a fault code like C1203.
• ABS Wheel Speed Sensor (-) Side Signal Voltage (for older passive sensors) — expected: 2.15 V to 3.5 V. Failure: Voltage outside this range for more than 140ms when vehicle speed is below 7 Km/h indicates an open or short.

Hidden / Shadow Codes Worth Checking

• Historical Fault Logs (e.g., cleared P0841): The Hyundai GDS scan tool has a 'Flight Record' function that can retrieve historical diagnostic data, including previously cleared fault codes and their freeze frame data. This is critical for diagnosing intermittent issues that don't leave a current active code. (see via Hyundai GDS (Global Diagnostic System) OEM scan tool.)

Scan Tool Commands That Help

• Hyundai GDS (Global Diagnostic System): Vehicle Software Management -> Resetting adaptive values — After replacing major transmission components like the valve body or internal harness, resetting the transmission's learned shift adaptations can resolve harsh or incorrect shifting.
• Hyundai GDS (Global Diagnostic System): Current Data -> Input speed and output speed sensors — This live data stream is the primary method for confirming a failed internal transmission harness. While driving, a technician will watch for the sensor readings to drop to zero or become erratic, confirming the signal loss that sets codes like P0717 or P0722.
• Hyundai GDS (Global Diagnostic System): Flight Record — For intermittent shifting problems or warning lights without an active code, the Flight Record function can be used to capture data from the last ten minutes of operation when a problem occurs, or to review historical faults that have been cleared.

Wiring & Ground Locations

• ABS Control Module — Located in the engine compartment, below the brake master cylinder. On some models, it is under the air filter box.. This is the central module that receives signals from all wheel speed sensors. The main connector here is a primary test point for checking sensor circuits.
• G07 (Ground) — Located behind the driver's side front kick panel.. This is a key chassis ground point. A loose or corroded ground here can cause a variety of difficult-to-diagnose electrical issues, including erratic behavior from the ABS or other control modules.
• ABS/ESC Harness Chafe Point — The main harness may rub against the metal bracket that runs under the headlight to the radiator.. This can cause an intermittent short in the wheel speed sensor wiring, leading to codes like C1203 even if the sensor itself is good. The fix involves repairing the wires and insulating the bracket.

Real Owner Repair Stories

• YouTube channel 'Pine Hollow Auto Diagnostics' (2011 Hyundai Santa Fe) — Check Engine, ABS, Traction Control, and 4WD warning lights are on.
  ❌ Tried (didn't work) The story begins with diagnosis, not failed repairs.
  ✅ What actually fixed it A professional scan revealed codes C1203 (Right Front Sensor Open or Short), P1751 (Right Front Speed Sensor), and P2159 (Vehicle Speed Sensor B). All codes pointed to a single faulty front right ABS wheel speed sensor, which was replaced to fix the issue.

OEM Part Supersession History

• 46307-3B610, 46307-3B620 → 46307-3B650 — Revision and consolidation of the part for improved reliability or manufacturing.
  Heads up: While the new part number (46307-3B650) replaces the old ones, it is critical to use the superseded part. Using an old stock or used version of the original part numbers risks repeating the original failure.

Model Year Variations Within This Range

• 2010: There was a mid-year production split on or around 06/11/2010 for the automatic transmission. While the OEM part number may appear the same, forum discussions indicate potential subtle differences in wiring or computer logic that could affect interchangeability of used transmissions.
• 2010-2012: The 2.4L 4-cylinder engine is typically paired with the A6MF2 transmission, while the 3.5L V6 is paired with the more robust A6LF2 transmission to handle the higher torque.

Diagnostic Flowchart

Other Known Issues on This Vehicle

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

• Faulty Fuel Level Sensor 🟠 Medium — Common issue, often occurring around 80,000-100,000 miles. Causes erratic fuel gauge readings and a Check Engine Light. (Ref: No official recall, but a very widely documented problem. Repair is costly due to labor involving dropping the fuel tank.)
• Oil Leak from Timing Cover 🟠 Medium — A notable issue where the sealant for the timing cover fails, leading to oil leaks at the front of the engine. If left unattended, oil can drip onto the alternator, causing it to fail. (Ref: A service campaign (TSB# 15-01-031) was issued for earlier 3.3L models (2007-2009) for a similar valve cover leak onto the alternator.)
• Clock Spring Failure 🔴 High — Extremely common failure leading to an airbag warning light and non-functional steering wheel controls (cruise, audio). (Ref: Hyundai extended the warranty for the clock spring to 15 years/unlimited miles under TSB 21-BE-003H-1, covering 2007-2012 Santa Fe (CM) models.)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: A used part is generally not recommended for either of the primary fixes. However, if budget is the absolute priority, a used ABS sensor from a low-mileage, non-corrosion-area donor vehicle could be attempted, but it carries significant risk of premature failure.

Donor-vehicle mileage cap: roughly under 75000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• For a used ABS sensor, inspect the wiring for any cracks, brittleness, or damage.
• Ensure the connector is clean, with no bent or corroded pins.
• Avoid parts from vehicles in the salt belt, as corrosion is a primary failure mode.

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

• Internal Transmission Wire Harness (46307-3B650): This part fails from heat and age. A used part is already degraded and installing it requires significant labor, making failure a costly gamble. Always buy this part new from Hyundai to get the latest revised version.

Aftermarket brands forum-validated for this vehicle:

• ABS Wheel Speed Sensor: Brands like Bosch, Delphi, and Standard Motor Products (SMP) are generally considered reliable aftermarket choices. AIP Electronics is another available brand.

Brands owners have reported issues with on this vehicle:

• Unbranded, no-name harnesses or sensors from online marketplaces should be avoided. The quality of the wiring, insulation, and sensor components is critical for longevity and proper signal, and these are often where cheap parts cut corners.

Real Owner Stories

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

Related OBD-II Codes

• P0717 — Input Speed Sensor Circuit No Signal; often the actual code hidden behind a phantom P1720, indicating a failure in the internal transmission harness.
• P0721 — Output Speed Sensor Circuit Range/Performance; identified in TSB 14-AT-013 as a code requiring internal harness replacement.
• P0722 — Output Speed Sensor Circuit No Signal; frequently appears alongside P0717 when the internal transmission wire harness degrades.
• C1203 — Right Front Wheel Speed Sensor Open or Short; a chassis code that can trigger a generic P1720 reading on basic scanners.
• P2159 — Vehicle Speed Sensor 'B' Range/Performance; relates to the rear wheel speed sensor and is a common underlying cause for the symptoms associated with P1720.
• P0711 — Transmission Fluid Temperature Sensor Performance; this sensor is part of the same internal transmission wire harness that commonly fails on this vehicle.

Frequently Asked Questions