P0743 on 2011-2014 Kia Optima Hybrid: TCC Solenoid Circuit Fault Causes and Fixes

What's Unique About the 2011-2014 Kia OPTIMA HYBRID

For this specific generation of Kia Optima Hybrid and its platform-mate, the Hyundai Sonata Hybrid, the P0743 code is a well-documented issue related to the A6MF1 6-speed automatic transaxle. Kia released a Technical Service Bulletin (TSB TSBTRA051R1) that directly addresses this and several other solenoid-related codes. The bulletin explicitly advises technicians to replace the individual solenoids rather than the entire, much more expensive, transmission assembly, which is a common misdiagnosis.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Check Engine Light is on
• Reduced fuel economy
• Engine RPM is higher than normal at highway speeds
• Transmission may shift harshly or erratically
• Vehicle may enter 'limp mode', often stuck in 3rd gear
• Stalling when coming to a stop after cruising at highway speeds.

Most Likely Causes

1. Failed Torque Converter Clutch (TCC) Solenoid 🔴 High Probability This is a known failure point for this platform's A6MF1 transmission, as documented in Kia TSB TSBTRA051R1.
   How to confirm: After accessing the solenoid, a technician can test its resistance with a multimeter. A reading outside the manufacturer's specification of 2.7-3.4 Ohms at 68°F (20°C) confirms failure. An audible 🎬 See how to perform a solenoid resistance and click test. click test can also be performed by applying 12V, but an out-of-spec resistance is the definitive electrical test.
   Typical fix: Replace the faulty TCC solenoid (Part No. 46313-3B665). It is located on the valve body, accessible after removing the side cover of the transmission. 🎬 Watch: Step-by-step guide to removing and replacing the solenoids.
   Est. part cost: $40-$90
2. Damaged Internal Transmission Wiring Harness 🟡 Medium Probability The internal harness (Part No. 46307-3B650) is subjected to constant heat and vibration within the transmission, which can cause wires to become brittle, insulation to crack, or connector pins to fail, leading to an open or short circuit. It is often replaced as a preventative measure during solenoid replacement.
   How to confirm: Once the transmission side cover is removed, visually inspect the harness for any signs of burnt plastic, chafed wires, or damage at the connectors. Check for continuity on each wire from the solenoid connector to the main harness plug.
   Typical fix: Replace the internal wiring harness. This is often done at the same time as a solenoid replacement.
   Est. part cost: $50-$100
3. Low or Dirty Transmission Fluid ⚪ Low Probability
   How to confirm: Check the transmission fluid level and condition. If the fluid is dark, burnt-smelling, or contains debris, it can clog passages and cause solenoid issues. However, for P0743, this is less likely to be the root cause than a direct electrical failure.
   Typical fix: Perform a transmission fluid and filter change. The correct fluid for this vehicle is Kia SP-IV. This is required anyway when performing the solenoid replacement.
   Est. part cost: $75-$150
4. Damaged Wiring or Connectors (External) ⚪ Low Probability
   How to confirm: Visually inspect the external transmission wiring harness for any signs of damage, corrosion, or loose connections. Pay close attention to where the harness passes near hot or moving parts.
   Typical fix: Repair or replace the damaged section of the wiring harness.
   Est. part cost: $20-$300

Rare But Worth Checking

• Faulty Powertrain Control Module (PCM): This is very rare. The PCM should only be considered after all other possibilities, including solenoids and all internal/external wiring, have been exhaustively tested and ruled out. The TSB also suggests this as a final step if codes return after solenoid replacement.

Diagnosis Steps

1. Scan the vehicle's computer for P0743 and any other stored codes.
2. Check the transmission fluid level and condition. Ensure it is full and clean. The correct fluid is Kia SP-IV. Note: The Optima Hybrid does not have a transmission dipstick; the level is checked via a plug on the transmission case when the vehicle is level.
3. Inspect the external transmission wiring harness and connectors for any visible damage, corrosion, or loose connections.
4. If fluid and external wiring are okay, drain the transmission fluid and remove the transmission's side valve body cover to access the solenoids.
5. Visually inspect the internal wiring harness for any signs of burning, chafing, or damage.
6. Using a multimeter, test the resistance of the TCC solenoid. Disconnect its connector and measure across the two pins. Compare the reading to the manufacturer's specification of 2.7-3.4 Ohms at 68°F (20°C). An out-of-spec reading (often open circuit/infinite resistance) confirms a bad solenoid.
7. If the solenoid tests good, check for power and ground at the solenoid connector (via the harness) to trace the electrical fault further up the circuit toward the TCM. This can help isolate a harness vs. TCM issue.
8. If all wiring and solenoids test good, the issue may be with the PCM, but this is a last resort.

Parts You'll Likely Need

• Torque Converter Clutch (TCC) Solenoid (OEM #46313-3B665) — This is the most common failure part for code P0743 on this vehicle, as confirmed by a manufacturer TSB. Previous part numbers include 46313-3B661, 46313-3B060, and 46313-3B660.
  Trusted brands: Kia/Hyundai (OEM)
  OEM price range: $40-$90
  Aftermarket price range: $30-$70
• Internal Transmission Wire Harness (OEM #46307-3B650) — This harness connects the solenoids to the main transmission connector and is a common secondary failure point due to heat and vibration. It is often replaced preventatively with the solenoids.
  Trusted brands: Kia/Hyundai (OEM)
  OEM price range: $50-$100
  Aftermarket price range: $40-$80
• Transmission Fluid (Kia SP-IV) — The transmission must be drained to access the solenoid, requiring a fluid replacement. Approximately 5-6 quarts are needed for a drain and fill.
  Trusted brands: Kia (OEM), Idemitsu, ENEOS
  OEM price range: $15-$25 per quart
  Aftermarket price range: $10-$18 per quart
• Transmission Valve Body Cover Gasket (OEM #45285-3B610) — The gasket for the transmission side cover should be replaced to prevent leaks after the repair.
  Trusted brands: Kia (OEM)
  OEM price range: $20-$40
  Aftermarket price range: $15-$30

Related Codes That Often Appear With This One

• P0741 — This code indicates 'Torque Converter Clutch System - Stuck Off' and often appears with P0743 as it can be caused by the same failing solenoid, either electrically or mechanically.
• P0748, P0753, P0758, P0763, P0768, P0773 — These are all electrical fault codes for other transmission solenoids. Kia TSB TSBTRA051R1 groups them with P0743 as they often share a common cause related to the solenoid pack or internal harness.

Technical Service Bulletins (TSBs) & Recalls

• TSBTRA051R1: Provides information for replacing various shift solenoids, including for DTC P0743, on 6-speed automatic transaxles and advises against replacing the entire transaxle for this code.

Platform-Specific Known Issues

• A known issue documented by Kia TSB #TSBTRA051R1 involves the failure of various transmission solenoids, including the one responsible for P0743. The bulletin advises replacing the specific solenoid rather than the entire transaxle.
• Owner experiences on forums for both the Optima Hybrid and its platform-mate, the Sonata Hybrid, confirm that replacing the TCC solenoid and often the internal wire harness is the definitive fix for P0743 accompanied by limp mode and harsh shifting.

Mechanic-Grade Diagnostic Values

• TCC Solenoid (Damper Clutch Control Solenoid) Resistance — expected: 2.7 - 3.4 Ω at 20°C (68°F). Failure: A reading of infinite ohms (open circuit) or near zero ohms (short circuit).
• Variable Force Solenoids (VFS) Resistance (e.g., Pressure Control) — expected: 5.0 - 5.6 Ω at 20°C (68°F). Failure: Out of specification reading.
• On/Off Shift Solenoids Resistance — expected: 10 - 11 Ω. Failure: Out of specification reading.
• Transmission Fluid Temperature for Level Check — expected: 122°F - 140°F (50°C - 60°C). Failure: Checking the fluid level when the fluid is too cold or too hot will result in an inaccurate reading.

Scan Tool Commands That Help

• Kia GDS (Global Diagnostic System): Actuation Test / Solenoid Drive Test — This function allows a technician to command the TCC solenoid on and off to verify its mechanical operation (listening for a click) and to see if the command changes the circuit's electrical state, helping to isolate a faulty solenoid from a wiring issue without full disassembly.
• Kia GDS (Global Diagnostic System): Resetting Adaptive Values — After replacing a solenoid or the valve body, the transmission's adaptive learning values should be reset. This forces the TCM to relearn the shift points and clutch engagements with the new components, ensuring smooth operation.

Wiring & Ground Locations

• TCC Solenoid Location — Inside the transmission, on the valve body. It is one of eight solenoids on the Generation 1 valve body used in this vehicle range. A diagram is required for positive identification.. This is the physical component that must be accessed and tested/replaced to fix a P0743 electrical fault.
• Main Transmission Ground — Typically bolted to the transmission case itself, with a strap connecting to the vehicle's chassis/frame.. A poor or corroded main ground for the transmission can cause a variety of electrical issues and fault codes, including solenoid circuit errors. While not a primary cause, it should be checked for integrity.

OEM Part Supersession History

• 46313-3B060, 46313-3B660, 46313-3B661 → 46313-3B665 — Part revision and improvement by the manufacturer.
  Heads up: The latest part number (46313-3B665) is the correct replacement for the earlier versions and should be used for this repair.

Model Year Variations Within This Range

• 2011-2014: The A6MF1 transmission in this range uses a 'Generation 1' valve body with 8 solenoids. Newer Kia/Hyundai 6-speed transmissions may use a 'Generation 2' valve body with only 7 solenoids. It is critical to use parts and diagrams specific to the Generation 1 design.