P0758 on 2011-2015 Kia Optima: Shift Solenoid 'B' Electrical Fault Guide

What's Unique About the 2011-2015 Kia OPTIMA

For the 2011-2015 Kia Optima with the 6-speed automatic (A6MF1/A6GF1), this code is specifically addressed by a manufacturer's Technical Service Bulletin (TSB). The TSB, #TSBTRA051R1, explicitly instructs technicians to replace the faulty shift solenoid rather than the entire transaxle assembly. This is a crucial piece of information that can save owners thousands of dollars by avoiding an unnecessary and expensive transmission replacement, a scenario often initially quoted by shops unfamiliar with the TSB.

Diagnostic Flowchart

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

Symptoms You May Notice

• Harsh or jerky shifting, especially the 2-3 shift.
• Transmission failing to shift into or out of a specific gear.
• Transmission getting stuck in 'limp mode' (often 3rd gear).
• Illuminated Check Engine Light.
• Transmission slipping.
• Inability to shift into 2nd or 6th gear.
• Decreased fuel efficiency.

Most Likely Causes

1. Failed Shift Solenoid 'B' 🔴 High Probability → Shop Transmission Valve Body This is a widely known issue documented by Kia's own Technical Service Bulletin (TSBTRA051R1), which points to solenoid failure as the primary cause for this code on the A6MF1/A6GF1 transmission. The solenoid coil can burn out or develop an internal short/open circuit.
   How to confirm: A technician can test the solenoid's internal resistance with a multimeter after removing the transmission pan and valve body cover. The specification for this on/off solenoid is approximately 10–11 Ohms. A reading of infinity (open) or zero (short) confirms failure. A bidirectional scan tool can also command the solenoid on and off to check for a response.
   Typical fix: Replace the faulty shift solenoid. This involves draining the transmission fluid, removing the oil pan, removing the valve body cover, and swapping the solenoid on the valve body.
   Est. part cost: $80-$150
2. Wiring or Connector Issue 🟡 Medium Probability The internal transmission wiring harness is submerged in hot transmission fluid and can become brittle and crack over time, leading to shorts or open circuits. External wiring can also be damaged by heat and vibration.
   How to confirm: Visually inspect the internal harness for cracked insulation or broken wires when the pan is off. Test for continuity from the main transmission connector pins to the solenoid connector on the valve body. For Solenoid 'B' (2-6 Brake), this is often between pins 5 (power) and 11 (control) on the main connector.
   Typical fix: Repair the damaged section of the external wiring harness or replace the entire internal transmission wiring harness (OEM Part # 46307-3B650). Many mechanics recommend replacing the harness whenever a solenoid is replaced.
   Est. part cost: $10-$50 for external repair, $70-$120 for internal harness.
3. Low or Dirty Transmission Fluid ⚪ Low Probability → Shop Transmission Assembly While not a direct cause of an electrical fault code, contaminated fluid filled with clutch material and metal shavings can cause solenoids to stick, clog passages, and potentially short out electrically.
   How to confirm: Check the transmission fluid level and condition. If the fluid is dark, burnt-smelling, or contains visible debris, it is contaminated.
   Typical fix: Perform a transmission fluid and filter change. This is a prerequisite for any internal transmission work. If the fluid is extremely contaminated, it may indicate more severe internal damage.
   Est. part cost: $75-$150

Rare But Worth Checking

• Faulty Powertrain/Transmission Control Module (PCM/TCM): → Shop Transmission Assembly This is rare. The PCM/TCM should only be considered after the solenoid, wiring, and connectors have been thoroughly tested and ruled out. A fault in the solenoid's driver circuit within the module can mimic a solenoid or wiring failure.

Diagnosis Steps

1. Check the transmission fluid level and condition. Top off or change if necessary.
2. Use an OBD-II scanner to confirm P0758 and check for any other related codes.
3. Inspect the transmission external wiring harness and connectors for any visible damage, corrosion, or loose connections.
4. Using a professional scan tool, monitor the live data for the Shift Solenoid 'B' (2-6 Brake) current while driving. The current should change from low (~50mA) to high (~850mA) when the transmission shifts into 2nd or 6th gear.
5. If scan tool data is abnormal, test the solenoid resistance externally at the transmission case connector. For the A6MF1, test between pins 5 and 11. The reading should be between 10-11 Ohms.
6. If the resistance is out of spec, drain the transmission fluid and remove the oil pan and valve body cover to access the solenoids.
7. Visually inspect the internal wiring harness for brittle or broken wires.
8. Confirm the resistance of Shift Solenoid 'B' directly at the solenoid's terminals. If it fails the 10-11 Ohm test, it is bad.
9. If the solenoid tests good, check for battery voltage and a good ground at the solenoid's electrical connector on the harness with the key on. This will verify the integrity of the wiring from the TCM.
10. If the solenoid and wiring are confirmed to be good, the fault may lie with the Transmission Control Module (TCM).

Parts You'll Likely Need

• Automatic Transmission Control Solenoid (Shift Solenoid B, On/Off) (OEM #46313-3B600) — This is the most common failure part for code P0758 on this vehicle, as identified by the manufacturer's TSB and numerous owner accounts.
  Trusted brands: Kia/Hyundai (Genuine OEM), Standard Motor Products, Rostra
  OEM price range: $80-$120
  Aftermarket price range: $50-$100
• Automatic Transmission Internal Wire Harness (OEM #46307-3B650) — The internal harness is a frequent secondary failure point. The plastic insulation becomes brittle from heat and fluid exposure, causing wires to crack and short. It is highly recommended to replace this harness during solenoid service.
  Trusted brands: Kia/Hyundai (Genuine OEM)
  OEM price range: $70-$120
  Aftermarket price range: $60-$100
• Automatic Transmission Fluid — The fluid must be drained to access the solenoid and should be replaced with new fluid that meets Kia's SP-IV specification. A pan drop requires approximately 5 quarts.
  Trusted brands: Kia/Hyundai (Genuine OEM SP-IV), Idemitsu TLS-LV, Valvoline MaxLife ATF
  OEM price range: $15-$25 per quart
  Aftermarket price range: $10-$18 per quart
• Automatic Transmission Pan Gasket (OEM #45285-3B610) — The gasket should be replaced when the transmission pan is removed to ensure a proper seal and prevent leaks.
  Trusted brands: Kia/Hyundai (Genuine OEM), Fel-Pro, Mahle
  OEM price range: $20-$40
  Aftermarket price range: $15-$30

Related Codes That Often Appear With This One

• P0700 — P0700 is a generic code indicating that the Transmission Control Module (TCM) has stored a fault code. It often appears alongside more specific transmission codes like P0758 to signal a general transmission-related issue.
• P0763 — This is a code for Shift Solenoid 'C' Electrical. If multiple solenoid electrical codes appear together, it may point towards a shared power/ground issue in the wiring harness or a broader problem within the TCM affecting multiple driver circuits.

Technical Service Bulletins (TSBs) & Recalls

• TSBTRA051R1: Advises on the replacement of various shift solenoids for DTCs including P0758 on 6-speed automatic transaxles. It explicitly states not to replace the entire transaxle for this issue and that the repair can be done with the transaxle in the vehicle.

Platform-Specific Known Issues

• A Technical Service Bulletin (TSBTRA051R1) was issued by Kia for 2011-2013 models with the 6-speed automatic regarding this and other solenoid codes. It directs service technicians to replace the individual solenoids rather than the entire transaxle, confirming this is a recognized component-level failure.

Mechanic-Grade Diagnostic Values

• Shift Solenoid 'B' (On/Off type) internal resistance — expected: 10 - 11 Ohms. Failure: A reading of infinity (open circuit) or near-zero (short circuit).
• Voltage at transmission connector Pin 5 (Solenoid Power Supply 1) — expected: Approximately 12V with ignition on.. Failure: No or low voltage indicates a wiring issue from the PCM/TCM.

Scan Tool Commands That Help

• Kia GDS (Global Diagnostic System): Actuation Test for Shift Solenoid 'B' (2-6 Brake) — This command allows a technician to manually energize and de-energize the solenoid with the engine off (ignition on) to listen for the characteristic 'click' of a functioning solenoid. It helps confirm if the solenoid is mechanically stuck or if the wiring and control circuit from the TCM are working correctly.

Wiring & Ground Locations

• Transmission Main Connector — On the top or side of the transmission case, where the main vehicle harness connects to the transmission.. This is the primary external test point. Pin 5 provides power to Solenoid 'B', and Pin 11 is the control line from the TCM. Testing resistance between these two pins from the harness side allows for a quick check of the solenoid and internal wiring without removing the pan.

Real Owner Repair Stories

• YouTube Channel 'TCU/ECU Repair Guide' (Kia Forte (with same A6MF1 family transmission)) — Transmission jerking, fault codes P0763 (Solenoid C) and P0758 (Solenoid B) present.
  ❌ Tried (didn't work) Initial diagnosis pointed to solenoids or wiring, but the actual fault was upstream.
  ✅ What actually fixed it The power driver ICs (integrated circuits) for solenoids B and C on the Transmission Control Unit (TCU/ECU) circuit board had failed. Replacing the specific ICs on the board resolved the fault codes and restored normal operation.

OEM Part Supersession History

• 46307-3B610, 46307-3B620 → 46307-3B650 — Revisions to improve durability and resistance to heat and fluid degradation.
  Heads up: The newer 46307-3B650 harness is backward compatible with vehicles that originally used the -3B610 or -3B620 parts.

Model Year Variations Within This Range

• 2014-2015: The Kia Optima received a mid-generation facelift for the 2014 model year, which included cosmetic and interior updates. However, the powertrain options, including the 2.4L and 2.0L Turbo engines with the A6MF1/A6MF2 6-speed automatic transmission, remained the same. Therefore, the causes, diagnosis, and repair for code P0758 are identical across the entire 2011-2015 range.