🧭 Diagnostic Flowchart 🎬 Helpful Videos

P0720 on 2009-2022 Kia Forte: Output Speed Sensor Circuit Causes and Fixes

Q: My 2020 Kia Forte is hesitating and showing transmission codes; is there a specific TSB for this?

Yes, TSB TRA102 (also known as SA424) applies to 2019-2021 Forte models with the IVT. it addresses hesitation and transmission codes through a TCM software update or potential IVT replacement.

Q: I have a 2015 Forte with P0720. Should I just replace the Output Speed Sensor?

On 2009-2018 6-speed models, the sensors are integrated into a plastic internal wiring harness. It is highly recommended to replace the entire harness assembly (which includes the input, output, and temperature sensors) because the plastic harness itself often becomes brittle and fails due to being submerged in hot fluid.

Q: What specific transmission fluid should I use for my Kia Forte after replacing the sensor harness?

The manufacturer specification for these transmissions is Kia SP-IV fluid.

Q: Can a faulty speed sensor cause my speedometer to stop working?

Yes, a symptom of a P0720 failure on the Kia Forte is a speedometer that reads 0 mph or behaves erratically, as the Output Speed Sensor (OSS) provides the necessary speed data.

Q: Is the P0720 code related to the engine knocking issues common in these years?

No. While 2010-2021 models are prone to Theta II, Nu, or Gamma engine failures (often involving knocking and oil consumption), P0720 is specifically a transmission circuit code related to the Output Speed Sensor and its internal harness.

Q: Does the IVT software update apply to the 2022 Forte as well?

The context specifically cites TSB TRA102 for 2019-2021 Forte models. While the IVT is used in 2022 models, the specific bulletin mentioned covers up to the 2021 model year.

On 2009-2018 Fortes with the 6-speed automatic, P0720 is almost always a failed internal Output Speed Sensor. The sensor is inside the transmission, making replacement a labor-intensive job. For 2019+ models with the IVT/CVT, this code is less common, and transmission issues often point to other problems.

21 minutes to read 2009-2022 Kia Forte

Most Likely Cause

Faulty Internal Output Speed Sensor (OSS) / Wiring Harness

Difficulty

5/5

Est. Time

3.5 hrs

DIY Doable?

🔧 Shop

Shop Labor

$350 – $700

Parts Price

$50 – $150

⚠️ Drivable, but... — You can drive, but it's not recommended. The transmission may shift harshly, unpredictably, or get stuck in one gear (limp mode), making the vehicle unsafe in traffic. Continued driving could put extra stress on the transmission and potentially lead to more severe internal damage.

Key Takeaways

P0720 on a Kia Forte points to a problem with the Output Speed Sensor, which is crucial for proper shifting.
For 2009-2018 models with a 6-speed automatic, the sensor is inside the transmission, making this a difficult DIY repair. The input and output sensors are often replaced together.
For 2019+ models with the IVT/CVT, transmission issues are common but usually trigger different codes and may be covered by a service campaign.
Symptoms include harsh shifting, a non-working speedometer, and the vehicle may enter a 'limp mode'.
Driving with this code is not recommended due to unpredictable shifting, which can be a safety hazard.

The trouble code P0720 stands for 'Output Speed Sensor Circuit Malfunction'. The Output Speed Sensor (OSS) tells the Transmission Control Module (TCM) how fast the transmission's output shaft is spinning. This information is critical for scheduling gear shifts, operating the speedometer, and managing cruise control. When the TCM receives an erratic, intermittent, or no signal from the OSS, it triggers the P0720 code and illuminates the Check Engine Light.

What's Unique About the 2009-2022 Kia Forte

The key difference for the Kia Forte lies in the transmission type. Models from 2009-2018 typically use a 6-speed automatic transmission (A6GF1 family) where the input and output speed sensors are located inside the transmission, mounted to the valve body. This makes replacement much more complex than for externally mounted sensors. Later models from 2019 onwards often feature an Intelligent Variable Transmission (IVT), which is a type of CVT. While P0720 can occur, these IVT units have known issues covered by service bulletin TRA102 for different codes (like P0730, P0741) that often require a software update or complete unit replacement due to symptoms like slipping, shuddering, or total failure at low mileage.

🎬 Watch: A mechanic's warning about these specific Kia transmission models.

Generation note: The vehicle range covers three generations, with a major transmission change: - First Gen (TD, 2009-2013) & Second Gen (YD, 2014-2018): Typically equipped with a 6-speed A6GF1 automatic transmission. P0720 on these models most often points to the internal speed sensor harness failing due to heat and fluid exposure. The switch from a 4-speed to the 6-speed A6GF1 around 2011 is the key change; the 4-speed used an easier-to-access external sensor, while the 6-speed moved it inside the transmission. - Third Gen (BD, 2019-2022): Primarily uses an IVT (CVT). Transmission problems on these models are common but usually manifest with other codes (P0730, P0731, P0741, P0867) and are addressed by specific TSBs like TRA102 for software updates or IVT replacement due to internal slippage.

Professional service recommended: On the most commonly affected models (2009-2018), the sensor is inside the transmission pan, requiring removal of the valve body. This is a complex job that can lead to further transmission damage if done incorrectly. The job requires draining fluid, dropping the pan, and removing the valve body assembly to access the sensor harness.

Symptoms You May Notice

Check Engine Light is on
Harsh, erratic, or delayed shifting
Transmission getting stuck in one gear (limp mode)
Speedometer reads 0 mph or behaves erratically
Cruise control does not work
Engine may stall when coming to a stop
Decreased fuel efficiency
RPMs jumping with jerking or shuddering, especially on IVT models.

⚠️ Don't Waste Money on the Wrong Fix

Replacing the external Vehicle Speed Sensor (VSS) located on the wheel hub (ABS sensor). While this sensor also measures speed, P0720 specifically refers to the transmission's *output* shaft speed sensor.
Replacing only one of the internal sensors (input or output) when the entire harness assembly is the actual point of failure.

Most Likely Causes

Faulty Internal Output Speed Sensor (OSS) / Wiring Harness 🔴 High Probability On 6-speed automatic models (2009-2018), the sensors and their wiring are integrated into a single plastic harness located inside the transmission. This harness is constantly submerged in hot transmission fluid, which makes the plastic brittle over time, leading to cracks and circuit failures.
How to confirm: A diagnostic scan tool can monitor the OSS data stream. If the reading is zero or erratic while the vehicle is moving, the sensor or its circuit is bad. Resistance can also be checked with a multimeter if the sensor is accessed, comparing it to manufacturer specs. However, since the failure is often the harness itself, a visual inspection after removing the valve body is the most definitive confirmation.
Typical fix: Replace the entire input/output speed sensor wiring harness assembly. Since it contains the input sensor, output sensor, and transmission temperature sensor, it is common practice and highly recommended to replace the entire harness as a unit. 🎬 See this walkthrough on diagnosing output speed sensor codes. This requires draining the transmission fluid, removing the oil pan, and removing the valve body to access the harness.
Est. part cost: $40-$100
Damaged Internal Wiring Harness 🟡 Medium Probability → Shop Transmission Wiring Harness The wiring harness that holds the input and output speed sensors is plastic and lives inside the hot transmission fluid, which can make it brittle and prone to failure over time. This is the primary failure mode for P0720 on the A6GF1 transmission.
How to confirm: A visual inspection after removing the valve body may reveal cracked or damaged wiring. A continuity test on the harness wires can confirm an open or short circuit.
Typical fix: Replace the entire input/output speed sensor wiring harness assembly. This part often includes both sensors and the temperature sensor.
Est. part cost: $50-$100
Low or Contaminated Transmission Fluid ⚪ Low Probability → Shop Transmission Assembly While not a direct cause of a circuit code, very low or dirty fluid can cause erratic shifting, high temperatures, and transmission slippage, which can stress electrical components within the transmission and potentially trigger various codes.
How to confirm: Check the transmission fluid level and condition (if a dipstick is available). On sealed transmissions, this must be checked by a professional. The fluid should be red and clear, not brown, black, or smelling burnt.
Typical fix: Perform a transmission fluid drain and fill, or a full fluid exchange, using the correct specification fluid (e.g., Kia SP-IV).
Est. part cost: $80-$200 for fluid

Rare But Worth Checking

Faulty Transmission Control Module (TCM) or Powertrain Control Module (PCM): → Shop Engine Control Module (ECM) This is very uncommon. Before condemning the control module, all other possibilities, including the sensor, wiring, and fluid, must be exhaustively ruled out.

Diagnosis Steps

Connect an OBD-II scanner to confirm the P0720 code and check for any other related transmission codes, especially P0715 and P0711.
Use the scanner's live data function to monitor the Output Speed Sensor (OSS) signal while driving. A reading of 0 MPH or an erratic reading while the car is moving points to a problem with the sensor or its circuit.
Check the transmission fluid level and condition. Low or burnt fluid can indicate larger transmission problems.
If the OSS signal is faulty, the next step for 2009-2018 models is to access the internal sensor harness. This requires draining the fluid and removing the transmission oil pan and valve body.
Visually inspect the sensor and its wiring harness for any signs of damage, like cracks, brittle plastic, or burnt spots.
Test the sensor's resistance with a multimeter and compare it to the manufacturer's specifications. Test the wiring harness for continuity.
If the sensor or harness is faulty, replace the entire harness assembly. It is highly recommended to replace the input and output sensors together as they are on the same harness.
Reassemble the transmission, refill with the correct type and amount of new transmission fluid (e.g., Kia SP-IV), and clear the trouble codes.
Perform a test drive to ensure the transmission is shifting correctly and the P0720 code does not return.

Parts You'll Likely Need

Transmission Input/Output Speed Sensor Harness (OEM #42620-26001 (Verify for A6GF1)) — This is the most common failure point for P0720 on 6-speed automatic models (A6GF1). The harness typically includes both the input and output sensors and the temperature sensor, and is replaced as a single unit.
Trusted brands: Kia/Hyundai (Genuine OEM), Dorman, Standard Motor Products (SMP)
OEM price range: $70-$120
Aftermarket price range: $40-$80
Automatic Transmission Fluid — The transmission fluid must be drained to access the sensor and must be replaced with new fluid of the correct specification (e.g., Kia SP-IV).
Trusted brands: Kia (Genuine OEM), Idemitsu, Valvoline
OEM price range: $15-$25 per quart
Aftermarket price range: $10-$18 per quart
Transmission Pan Gasket — The old gasket should be replaced when the transmission pan is removed to prevent leaks.
Trusted brands: Kia (Genuine OEM), Fel-Pro, Mahle
OEM price range: $20-$40
Aftermarket price range: $10-$25

Related Codes That Often Appear With This One

P0715 — Input Speed Sensor Circuit Malfunction. On many Kia models with the A6GF1 transmission, the input and output sensors are on the same internal harness and often fail or are replaced together.
P0711 — Transmission Fluid Temperature Sensor Circuit Range/Performance. This sensor is also part of the same internal wiring harness that fails, so it is very common to see this code alongside P0715 and P0720.
P0721, P0722, P0723 — These are related codes indicating specific faults with the output speed sensor signal, such as range/performance issues, no signal, or intermittent signal.

Technical Service Bulletins (TSBs) & Recalls

TSB TRA102: IVT Software Logic Improvement and/or IVT Replacement for 2019-2021 Forte, Soul, and Seltos models.
TSB CHA121: Addresses intermittent noise when turning the steering wheel on 2019-2024 Forte models by replacing the front strut bearing and upper spring pad.

Platform-Specific Known Issues

For 2019-2021 Forte models with the IVT, there is a service bulletin (TRA102 / SA424) for issues including hesitation and various transmission codes (P0730, P0731, P0741, P0867). The fix involves a TCM software update and, in some cases, a complete IVT replacement.
Owner Experience: Replacing Parts Without Fixing the Problem: A common story on owner forums involves replacing the individual input and output sensors without success. One owner of a platform-mate Hyundai Elantra reported replacing both sensors and flushing the fl

Mechanic-Grade Diagnostic Values

Output Speed Sensor (OSS) internal resistance — expected: Approx. 5.8 MΩ (Megaohms). Failure: A reading that is significantly different, open (OL), or shorted (near 0 Ω).
Input Speed Sensor (ISS) internal resistance — expected: Approx. 3.8 MΩ (Megaohms). Failure: A reading that is significantly different, open (OL), or shorted (near 0 Ω). Tested as it's on the same harness.
Sensor reference voltage at harness connector — expected: 5.0V ± 0.5V. Failure: No voltage or voltage outside this range points to a wiring or TCM issue, not a sensor failure.

Scan Tool Commands That Help

Kia GDS (Global Diagnostic System) or equivalent professional scanner: Resetting Auto T/A Values / Init Of TCU Learning — This procedure is required after replacing the transmission, valve body, or the speed sensor harness. It clears the old learned shift adaptations from the TCM. Failure to perform this reset can result in continued poor shifting even with new parts. After the reset, a specific 'relearn' drive cycle must be performed to teach the TCM the characteristics of the new components.

Wiring & Ground Locations

Transmission Case Ground — A ground cable that connects the transmission case directly to the chassis.. A poor ground connection for the transmission can introduce electrical noise and voltage drops, potentially causing erratic signals from sensors housed within it. For 2014-2016 models, a specific ground cable is listed as OEM part 91860-A7220. Checking the integrity of this ground is a key diagnostic step before condemning internal components.
TCM/PCM Connector Pins — At the main connector for the Transmission or Powertrain Control Module.. To definitively rule out a wiring issue between the transmission and the control module, a continuity test is required. This involves identifying the specific pins for the OSS signal at the transmission's main external connector and the corresponding pins at the TCM. While a public, model-year-specific pinout is difficult to find, a technician would use service data to locate these pins and check for resistance (should be <1 Ω) and for shorts to ground or power.

Real Owner Repair Stories

Go-Parts article citing a Reddit user (2016 Hyundai Elantra (platform-mate with identical A6GF1 transmission)) — P0722 code (No Output Speed Signal), which is functionally similar to P0720.
❌ Tried (didn't work) Replacing the internal speed sensor three times., Replacing the entire transmission with a used unit.
✅ What actually fixed it The code immediately returned after the transmission replacement. The strong implication is that the actual fault was in the vehicle's external wiring harness between the transmission and the TCM, a step that was overlooked, leading to an expensive and unnecessary transmission replacement.

OEM Part Supersession History

42620-26000 → 42620-26001 — Typically indicates a minor revision, material improvement, or change in supplier. The updated part is considered more reliable.
Heads up: The parts are interchangeable, but 42620-26001 should always be used if available.

Model Year Variations Within This Range

Approx. 2009-2010: Some early first-generation Fortes may have been equipped with a 4-speed automatic transmission. On these models, the output speed sensor is typically an external, individual sensor that is much easier and cheaper to replace.
Approx. 2011-2018: Models equipped with the 6-speed A6GF1 automatic have the infamous internal sensor harness. P0720 on these vehicles almost always points to this internal component, requiring valve body removal.

Diagnostic Flowchart

Start by confirming if the P0720 code is isolated or paired with other transmission codes like P0715 or P0711, as this platform often suffers from a specific internal harness failure.

Are you experiencing hesitation or codes P0730, P0731, or P0867 alongside P0720?

→ Check for TSB TRA102 / SA424. This likely requires a TCM software logic update or a complete IVT replacement under warranty.

Monitor Output Speed Sensor (OSS) live data while driving. Does the reading stay at 0 MPH or jump erratically?

Inspect the transmission fluid. Is it low, black, or smelling burnt?

→ Perform a fluid drain and fill using Kia SP-IV specification fluid. If symptoms persist, internal mechanical damage to the A6GF1 transmission is likely.

Are codes P0715 (Input Speed Sensor) or P0711 (Temp Sensor) also present?

→ This confirms a failure of the internal plastic wiring harness. On the A6GF1 transmission, heat makes this harness brittle. Replace the entire internal sensor harness assembly ($40-$100 part).

Drain fluid and remove the oil pan/valve body. Does a multimeter show an open circuit or out-of-spec resistance on the OSS?

→ Replace the integrated speed sensor harness. Do not attempt to replace just the sensor; the plastic harness is the known failure point on Forte and platform-mate Elantra models.

→ Inspect the TCM (Transmission Control Module) connectors for fluid wicking or corrosion. If wiring is perfect, the TCM itself may be failing to process the OSS signal.

→ The P0720 may be intermittent. Inspect external wiring connectors at the transmission case for corrosion or loose pins before proceeding to internal repairs.