P1720 on 2017-2022 Genesis G90: Understanding This Unconfirmed Code

What's Unique About the 2017-2022 Genesis G90

Genesis, as Hyundai's luxury brand, shares much of its diagnostic logic with Hyundai vehicles. The G90 uses a Hyundai-built 8-speed automatic transmission (A8TR1 for the 3.3T, A8LR1 for the 5.0L). Research into Hyundai platforms and official Technical Service Bulletins (TSBs) confirms that P1720 is not a valid code. Instead, it often masks other, more specific transmission speed sensor or wiring harness codes. Therefore, the focus should not be on fixing a 'P1720' but on using a more advanced, manufacturer-compatible scan tool to retrieve the true diagnostic trouble codes.

Symptoms You May Notice

• Check Engine Light is on
• Transmission may be stuck in one gear (limp mode)
🎬 Watch: What is limp mode and how to fix it
• Harsh, erratic, or delayed shifting
• Flashing gear position indicator on the dashboard
• Inaccurate or non-functional speedometer
• Vehicle hesitates or revs high before shifting
🎬 See: Common causes and symptoms of transmission limp mode

Most Likely Causes

1. Generic OBD-II Scanner Error 🔴 High Probability Manufacturer-specific codes (P1xxx) are often misinterpreted by basic, universal code readers.
   How to confirm: Re-scan the vehicle with a professional-grade diagnostic tool that has specific software for Hyundai/Genesis vehicles (such as a GDS). The tool will likely show different codes, such as P0717, P0721, or P0722, as outlined in Hyundai TSB 16-AT-013.
   Typical fix: No parts are replaced. The fix is obtaining an accurate diagnosis by using the correct equipment.
   Est. part cost: $0
2. Failed Internal Transmission Wiring Harness / Speed Sensor Assembly 🟡 Medium Probability → Shop Transmission Assembly On related Hyundai/Kia platforms using the same 8-speed transmissions, the internal harness which contains the input and output speed sensors can fail due to heat and fluid exposure over time. This is a known issue addressed by multiple Hyundai TSBs.
   How to confirm: A professional scan tool will show codes like P0717 (Input/Turbine Speed Sensor 'A' Circuit No Signal) or P0721/P0722 (Output Speed Sensor Circuit Range/Performance/No Signal). The technician can then test the sensor circuits from the transmission connector.
   Typical fix: The transmission fluid pan is removed to access and replace the internal wiring harness assembly (sometimes called an E-Module). The transmission fluid and filter are typically replaced at the same time.
   Est. part cost: $100-$200

Rare But Worth Checking

• Damaged External Transmission Connector or Wiring: → Shop Transmission Assembly
• Failed Powertrain Control Module (PCM) or Transmission Control Module (TCM): → Shop Engine Control Module (ECM)

Diagnosis Steps

1. STOP. Do not proceed with any repairs based on the P1720 code alone.
2. Take the vehicle to a qualified transmission shop or a Genesis/Hyundai dealership.
3. Have the vehicle scanned with a manufacturer-specific diagnostic tool (GDS) to retrieve the correct trouble codes from the Transmission Control Module (TCM).
4. If codes like P0717, P0721, or P0722 are present, follow the diagnostic procedure outlined in Hyundai TSB 16-AT-013.
5. This typically involves checking the wiring and connectors at the transmission for damage or corrosion.
6. Using the scan tool, monitor the live data for Input and Output speed sensor RPMs while driving. A lack of signal or erratic readings points to a sensor or wiring issue.
7. If the external wiring is intact, the next step is to drop the transmission oil pan, inspect the fluid, and replace the internal transmission wiring harness which contains the sensors.

Parts You'll Likely Need

• Automatic Transmission Wire Harness (OEM #46307-4G100 (Verify with VIN)) — This part often contains the input and output speed sensors that fail, triggering the true underlying codes that are misinterpreted as P1720.
  Trusted brands: Hyundai/Genesis OE
  OEM price range: $100-$200
  Aftermarket price range: $70-$150
• Automatic Transmission Fluid (OEM #SPH-IV or SP4-M (Check owner's manual)) — The transmission fluid must be drained to replace the internal harness and should be replaced with new, manufacturer-spec fluid.
  Trusted brands: Hyundai/Genesis OE, Idemitsu TLS-LV, Valvoline MaxLife ATF
  OEM price range: $20-$30 per quart
  Aftermarket price range: $10-$20 per quart

Related Codes That Often Appear With This One

• P0717 — This is a likely 'true' code for 'Input Speed Sensor Circuit No Signal' that a generic scanner might misinterpret as P1720.
• P0721 — This is a likely 'true' code for 'Output Speed Sensor Circuit Range/Performance' that could be misinterpreted as P1720.
• P0722 — This is a likely 'true' code for 'Output Speed Sensor Circuit No Signal' that could be misinterpreted as P1720.

Technical Service Bulletins (TSBs) & Recalls

• Hyundai TSB 16-AT-013: Specifically addresses DTCs P0717, P0721, P0722, & P0791 for the 2017+ Genesis G90 (HI), instructing technicians to replace the internal harness ('E-Module') rather than the entire transmission. This is the key document confirming the likely underlying issue.

Mechanic-Grade Diagnostic Values

• Continuity/Resistance of Speed Sensor Wiring — expected: Close to 1 ohm, with audible continuity tone. Failure: High resistance (OL or 'open loop') indicates a broken wire. No continuity tone confirms an open circuit.

Scan Tool Commands That Help

• Hyundai GDS (Global Diagnostic System): Resetting Auto T/A Values (Reset Adaptive Values) — This procedure is mandatory after replacing the transmission, valve body, internal harness, or reprogramming the TCM. Failure to reset the learned values can result in harsh shifting or shift flares even after the physical repair is complete.
• Hyundai GDS (Global Diagnostic System): AT Adaptation Mode (Relearn Adaptive Values) — After resetting the adaptive values, a specific driving relearn procedure must be performed. The GDS tool guides the technician through the process, which involves specific upshift and downshift patterns to allow the TCM to learn the new clutch fill times and pressure characteristics.

Wiring & Ground Locations

• Transmission Ground Wire Assembly — A dedicated wiring assembly that provides a ground path for the transmission.. A poor ground connection can cause erratic behavior and fault codes for various electronic components within the transmission, including the speed sensors. Verifying the integrity of this ground is a key electrical diagnostic step. Part numbers vary by configuration: 91880-B1510 (3.3L 2WD), 91880-B1520 (3.3L 4WD), 91880-B1530 (5.0L 2WD), 91880-B1540 (5.0L 4WD).

Real Owner Repair Stories

• Hyundai Forum user 'Accent09GLS' (2009 Hyundai Accent 1.6L (Note: This is a different vehicle/transmission, but illustrates the diagnostic process for the underlying P0717 code)) — Check Engine Light on, transmission shift problems.
  ❌ Tried (didn't work) Initial diagnosis from a generic scanner at an auto parts store.
  ✅ What actually fixed it The user identified the true code as P0717 (Input/Turbine Speed Sensor). On this specific vehicle (Accent), the sensor was located externally on the front/side of the transmission. The user replaced the sensor (NAPA part VSS 1022), which resolved the issue. This highlights how on other platforms the sensor is external, which can lead to misdiagnosis on the G90 where it is internal.

Model Year Variations Within This Range

• 2017-2022: The Genesis G90 received a significant exterior and interior facelift for the 2020 model year. However, the underlying platform and powertrains (3.3L V6 and 5.0L V8 with the A8TR1/A8LR1 8-speed automatic transmission) remained the same. Therefore, the causes and fixes for transmission speed sensor codes are consistent across the entire 2017-2022 range.

Diagnostic Flowchart

Other Known Issues on This Vehicle

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

• Carbon Buildup on Intake Valves (GDI) 🟠 Medium — Common on all Gasoline Direct Injection (GDI) engines, including the 3.3T and 5.0L. Becomes noticeable after 60,000 miles, potentially causing rough idle, misfires, and reduced performance.
• Electronic Wastegate Actuator (EWGA) Failure (3.3T) 🟠 Medium — A known failure point on the 3.3L twin-turbo engine. A distinct rattle or squeak upon engine shutdown is a common precursor to failure, which can cause underboost (P0299) or overboost (P0234) codes.
• Turbocharger Oil Feed Pipe Leak (3.3T) 🔴 High — The driver's side (Bank 2) turbo oil feed pipe is prone to cracking from heat, which can leak oil onto the hot exhaust manifold, creating a significant fire risk. (Ref: NHTSA Recall 24V-191 (Genesis Recall 019G))

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this specific repair, using a used part is not recommended. The primary failure part is the internal wiring harness, which is a relatively low-cost electronic component that fails due to heat and age. A used harness from a salvage yard would have unknown history and similar age-related wear, posing a high risk of premature failure.

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

• Internal Transmission Wiring Harness (E-Module): Due to the critical function and labor-intensive replacement process, using a genuine Hyundai/Genesis OE part (46307-4G100) is strongly recommended to ensure proper fitment, material quality, and longevity.

Brands owners have reported issues with on this vehicle:

• Unbranded/generic harnesses from online marketplaces should be avoided. While they may be cheaper, they often use lower-quality materials that may not withstand the transmission's harsh environment, leading to a repeat failure.

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/Turbine Speed Sensor 'A' Circuit No Signal; identified in TSB 16-AT-013 as a primary code often masked or misread as P1720.
• P0721 — Output Speed Sensor Circuit Range/Performance; a common actual code found when using a GDS tool on a vehicle reporting P1720 symptoms.
• P0722 — Output Speed Sensor Circuit No Signal; listed in TSB 16-AT-013 as a code resulting from a failed internal transmission wiring harness.
• P0791 — Intermediate Shaft Speed Sensor Circuit; another transmission sensor code specifically addressed by TSB 16-AT-013 for the Genesis G90 platform.
• P0299 — Turbocharger Underboost; a related engine code for the 3.3T G90 caused by Electronic Wastegate Actuator (EWGA) failure.
• P0234 — Turbocharger Overboost; can occur alongside EWGA issues on the 3.3L twin-turbo engine.

Frequently Asked Questions