P1778 on 2012-2014 Kia Soul: Transmission Solenoid Failure Causes and Fixes

What's Unique About the 2012-2014 Kia SOUL

The 2012-2014 Kia Soul, which spans the late first and early second generations, uses a 6-speed automatic transmission (A6GF1/A6MF1 family) where solenoid failures are a well-documented issue. Kia acknowledged this weakness by issuing Technical Service Bulletin TSBTRA051R1. This bulletin is critical because it specifically instructs technicians to replace the individual solenoids for code P1778 and a host of others, directly advising against the much more expensive replacement of the entire transaxle. This issue is systemic to this transmission family, affecting numerous Hyundai and Kia models.

Diagnostic Flowchart

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

Generation note: This range covers the end of the first generation (2012-2013) and the start of the second generation (2014). Both generations used a 6-speed automatic transmission (A6GF1 for 1.6L, A6MF1 for 2.0L) where this solenoid issue is known to occur.

Symptoms You May Notice

• Check Engine Light is on
• Harsh, erratic, or delayed shifting
• Vehicle is stuck in "limp mode" (often 3rd gear)
• Poor acceleration from a stop
• Transmission may feel like it's slipping or shuddering
• Delayed gear engagement when shifting from Park to Drive or Reverse
🎬 Watch: Common symptoms of a failing Kia transmission solenoid

Most Likely Causes

1. Failed Transmission Solenoid 🔴 High Probability This is a documented common failure point for the 6-speed automatic transmission used in this vehicle, as acknowledged by Kia's Technical Service Bulletin TSBTRA051R1. The solenoids, particularly the TCC solenoid, are known weak points.
   How to confirm: A mechanic can use an advanced scan tool to test solenoid operation. A definitive diagnosis involves removing the transmission pan and testing the resistance of the solenoid with a multimeter. A good on/off solenoid should read around 10-11 ohms, while VFS solenoids should be around 5.1-5.3 ohms. An open circuit (infinite resistance) or short circuit (zero resistance) confirms failure.
   Typical fix: Replace the faulty solenoid or the entire solenoid pack (8 solenoids) on the valve body. It is highly recommended to replace the internal wiring harness at the same time, as it is a frequent point of failure.
   Est. part cost: $60-$250 for a single solenoid or a full aftermarket kit.
2. Failed Internal Transmission Wiring Harness 🟡 Medium Probability The internal harness that connects the solenoids is subjected to constant heat and immersion in transmission fluid, causing the wires to become brittle and the connectors to fail over time. This is a very common failure point that can mimic a solenoid failure.
   How to confirm: After removing the transmission pan, a visual inspection of the harness is required. Look for brittle or cracked insulation, burnt connector pins, or other signs of heat damage.
   Typical fix: Replace the internal wiring harness. This is often done preventatively whenever the valve body is accessed to replace solenoids. The OEM part number is often 46307-3B650 or similar.
   Est. part cost: $70-$150

Rare But Worth Checking

• Low or Dirty Transmission Fluid: Fluid that is low, burnt, or contaminated with debris can cause solenoids to stick or operate poorly. Always check the fluid level and condition as a first step. Kia specifies SP-IV type fluid.
• Damaged Wiring Harness: External wiring to the transmission solenoids can become damaged or corroded, mimicking a solenoid failure. A visual inspection is necessary.
• Faulty Transmission Control Module (TCM): This is extremely rare. In some Kia/Hyundai models, leaking capacitors on the TCM/ECU circuit board can cause solenoid codes. This should only be considered after all solenoid and wiring issues have been ruled out.

Diagnosis Steps

1. Scan the vehicle to confirm P1778 is the active code and check for other related transmission codes.
2. Check the transmission fluid level and condition. The vehicle must be level and the fluid at operating temperature (122-140°F). The fluid should be at the correct level, pink/red in color, and not smell burnt.
3. Inspect the external transmission wiring harness and connectors for any visible damage, corrosion, or loose connections.
4. If external checks are clear, the vehicle should be lifted, the transmission fluid drained, and the transmission oil pan removed.
5. Visually inspect the internal wiring harness for brittle wires or burnt connector pins. This is a common point of failure.
6. Identify the suspect solenoid (TCC solenoid for P1778) and test its resistance with a multimeter. 🎬 See how to test solenoid resistance with a multimeter Compare the reading to the manufacturer's specification (typically 5-6 ohms for VFS solenoids, 10-11 ohms for on/off solenoids). An open circuit (infinite resistance) or short circuit (zero resistance) confirms failure.
7. It is highly recommended to replace all 8 solenoids as a kit and the internal wiring harness at the same time, due to the high labor overlap and common failure rate of all components.
8. Install a new transmission pan gasket, reinstall the pan, and refill with new, manufacturer-specified (SP-IV) automatic transmission fluid.
9. Clear the DTCs and perform a transmission adaptive values reset using an appropriate scan tool.

Parts You'll Likely Need

• Automatic Transmission Control Solenoid (OEM #46313-3B030) — This is the specific ON/OFF solenoid often identified for the TCC circuit fault that triggers P1778. However, many solenoids look similar.
  Trusted brands: Genuine Kia, Standard Motor Products, Duralast
  OEM price range: $75-$120
  Aftermarket price range: $60-$100
• Transmission Solenoid Kit (8-piece) — Due to the high labor cost to access the valve body, it is a common and recommended practice to replace all 8 solenoids at once to prevent future failures. 🎬 Watch: Step-by-step guide to replacing the solenoid pack
  Trusted brands: Rostra, Sonnax, Aftermarket kits on eBay/Amazon
  OEM price range: N/A
  Aftermarket price range: $150-$250
• Internal Transmission Wiring Harness (OEM #46307-3B650) — This is a known high-failure part that becomes brittle from heat. It is strongly recommended to replace it when replacing solenoids.
  Trusted brands: Genuine Kia/Hyundai
  OEM price range: $70-$150
  Aftermarket price range: $50-$100
• Automatic Transmission Fluid (ATF SP-IV) — The fluid must be drained to access the solenoids and must be replaced with new fluid that meets Kia's specific SP-IV standard.
  Trusted brands: Kia OEM, Idemitsu, Valvoline MaxLife
  OEM price range: $15-$25 per quart
  Aftermarket price range: $8-$15 per quart
• Automatic Transmission Pan Gasket — The old gasket is crushed during installation and must be replaced to prevent leaks when the pan is reinstalled.
  Trusted brands: Fel-Pro, Mahle, Beck/Arnley
  OEM price range: $20-$40
  Aftermarket price range: $10-$25

Related Codes That Often Appear With This One

• P0741 — Relates to the Torque Converter Clutch solenoid performance, which is part of the same valve body assembly and often the specific solenoid at fault for P1778.
• P0743 — Another code for the Torque Converter Clutch solenoid circuit.
• P0753, P0758, P0763, P0768, P0773 — These codes all point to electrical faults in the various shift solenoids (A, B, C, D, E) within the same transmission. They are all listed in TSB TSBTRA051R1 and the equivalent Hyundai TSB 19-AT-015H.
• P2709 — This code for Shift Solenoid 'F' is also included in the same family of solenoid electrical faults covered by the TSB.

Technical Service Bulletins (TSBs) & Recalls

• TSBTRA051R1: Advises on the replacement of various shift solenoids for a list of DTCs, including P1778, on vehicles with 6-speed automatic transaxles. It specifically warns against replacing the entire transaxle for these codes.
• Hyundai 19-AT-015H: The Hyundai equivalent of the Kia TSB, which also includes P1778 in its list of solenoid fault codes. This confirms the issue is tied to the transmission family used across both brands.

Platform-Specific Known Issues

• The 6-speed automatic transmission in this year range is known for solenoid failures, which prompted Kia to issue TSB TSBTRA051R1. The bulletin confirms that codes like P1778 are due to solenoid issues and should be fixed by replacing the solenoid, not the entire transaxle.

Mechanic-Grade Diagnostic Values

• Resistance of On/Off type solenoids (e.g., TCC, Shift Solenoid A/B) — expected: 10 - 11 Ω. Failure: A reading of infinity (open circuit) or near-zero (short circuit).
• Resistance of Variable Force Solenoids (VFS) / PWM Solenoids — expected: 5.1 - 5.3 Ω. Failure: A reading significantly outside this narrow range indicates a faulty solenoid.
• Transmission Fluid Temperature Sensor Resistance — expected: ~2.5 kΩ at 68°F (20°C). Failure: A reading far from this value at the specified temperature suggests a faulty sensor, which can cause incorrect shift commands.

Scan Tool Commands That Help

• Kia GDS/KDS (dealer scan tool): Resetting Auto T/A values — This function must be performed after replacing transmission solenoids, the valve body, or the entire transmission to clear the old adaptive learning data and force the TCM to relearn shift pressures and timing with the new components. Failure to do so can result in continued poor shift quality even after the repair.

Real Owner Repair Stories

• Owner forum for Hyundai Sonata (platform mate) (2011 Hyundai Sonata 2.4L (uses same A6MF transmission family)) — Harsh shifting and a P0741 code (Torque Converter Clutch System Performance), which is frequently seen with P1778.
  ❌ Tried (didn't work) Initial diagnosis was unclear without further testing.
  ✅ What actually fixed it A resistance test on the TCC solenoid showed an open circuit. The owner replaced the entire set of 8 solenoids and the internal wiring harness. They reported the transmission shifted 'like new' after the repair, confirming that replacing the solenoids and harness as a set is an effective solution.

OEM Part Supersession History

• 46307-3B610, 46307-3B620 → 46307-3B650 — Updated design, likely for improved heat resistance and durability. The updated harness integrates the temperature sensor, which was separate on some older versions.
  Heads up: While the older harnesses may physically connect, using the superseded part numbers is not recommended. The 46307-3B650 is the correct, most current replacement for this repair.
• 46313-3B020 → 46313-3B030 — Likely an internal revision for improved reliability or manufacturing consistency.
  Heads up: The new part number is a direct replacement for the old one.

Model Year Variations Within This Range

• 2012-2014: The internal transmission wiring harness may have an old or new style. Older harnesses had a separate, disconnectable Transmission Fluid Temperature (TFT) sensor. The updated harness (part #46307-3B650) integrates the TFT sensor directly into the harness. It is highly recommended to always replace an old-style harness with the updated, integrated version during solenoid replacement to prevent future issues.