P0700 on 2010-2013 Kia Forte: Transmission Control System Malfunction Guide

What's Unique About the 2010-2013 Kia Forte

For the first-generation Kia Forte (2010-2013), which used 4-speed (A4CF2) and 5-speed automatics early on, and primarily the 6-speed (A6GF1) automatic later in the generation, the P0700 code is frequently a precursor to more specific codes related to sensors. Unlike some vehicles where P0700 might point to severe internal issues, on this Forte, common culprits are often the inhibitor switch (neutral safety switch), the input/output speed sensors, or the transmission fluid temperature sensor (often part of the internal harness). These are relatively accessible and less expensive to fix than a full transmission rebuild.

Symptoms You May Notice

• Check Engine Light is on.
• Harsh, erratic, or delayed shifting.
• Vehicle may get stuck in one gear (limp mode).
• Inability to start the engine, or starting only in Neutral but not Park (or vice-versa).
• Flashing gear position indicator (PRNDL) on the dashboard.
• Gear position indicator may not show 'P' when in Park, preventing key removal.
• Decreased fuel economy.
• Speedometer may work erratically or not at all (classic sign of output speed sensor failure).
• Transmission overheating warning light may illuminate.

Most Likely Causes

1. Faulty Inhibitor Switch (Neutral Safety Switch) 🔴 High Probability This switch is exposed on the outside of the transmission and is a common failure point across many Kia/Hyundai models of this era. Its failure can cause a no-start condition or erratic shifting. Kia has issued service actions (e.g., SA317A/B/C for later models) for this part, indicating a known issue with the component.
   How to confirm: Scan the TCM for code P0705 (Transmission Range Sensor Circuit Malfunction). Test the switch by checking if the car starts in Neutral but not Park. A multimeter can be used to test the switch's continuity between specific pins for each gear position to see if it sends the correct signal to the TCM.
   Typical fix: Replace the inhibitor switch. This is located on the exterior of the transmission housing, usually accessible after removing the battery and air filter box. Proper alignment during installation is critical. 🎬 Watch: How to test and replace the inhibitor switch yourself.
   Est. part cost: $45-$70
2. Faulty Input or Output Speed Sensor 🟡 Medium Probability These sensors provide critical data for shift timing and are subject to failure from heat and vibration. An output speed sensor failure is particularly common and will often cause an erratic or dead speedometer along with harsh shifting.
   How to confirm: Scan the TCM for codes like P0717 (Input/Turbine Speed Sensor Circuit No Signal) or P0720/P0721 (Output Speed Sensor Malfunction). The resistance of the sensors can be checked with a multimeter against factory specs, though specific values are not consistently published; comparison with a new part is a common diagnostic method.
   Typical fix: Replace the faulty speed sensor. These are typically mounted externally on the transmission case and are relatively easy to access and replace.
   Est. part cost: $25-$85
3. Faulty Transmission Fluid Temperature Sensor 🟡 Medium Probability This sensor is often integrated into the internal wiring harness inside the transmission. A failure can cause the TCM to apply incorrect line pressure, leading to harsh shifting as it defaults to a safe temperature value (often 176°F/80°C). Kia TSB TRANS 043 specifically addresses this failure on the 6-speed automatic.
   How to confirm: Scan the TCM for codes P0711, P0712, or P0713. On a scan tool, watch the live data for the transmission fluid temperature. If it reads a fixed, illogical value (like -40°F or a very high number) or doesn't change as the car warms up, the sensor or its circuit is faulty.
   Typical fix: The sensor is part of the internal transmission wiring harness (valve body harness), which requires removing the transmission oil pan 🎬 See this walkthrough for replacing the temperature sensor and harness. and sometimes the valve body to access and replace.
   Est. part cost: $40-$100 for the harness assembly
4. Low or Dirty Transmission Fluid ⚪ Low Probability While not specific to this platform, neglected maintenance can lead to fluid breakdown, causing shifting issues, solenoid problems, or overheating. High-mileage transmissions that have never had a fluid change can sometimes develop problems after a full flush, as the new fluid can dislodge built-up varnish.
   How to confirm: Check the transmission fluid level and condition via the dipstick (if equipped). The fluid should be bright red and not smell burnt. If there is no dipstick, the level must be checked via a fill plug on the side of the transmission case with the vehicle level and at a specific temperature (typically 122-140°F / 50-60°C for the A6GF1).
   Typical fix: Perform a transmission fluid drain-and-fill. A full fluid exchange is generally not recommended on high-mileage, poorly maintained transmissions. Always use fluid that meets Kia's specifications (e.g., SP-III for the 4-speed, SP-IV for the 6-speed).
   Est. part cost: $50-$150 for fluid and filter

Rare But Worth Checking

• Faulty Shift Solenoid or Valve Body: While less common than sensor failures, a specific shift solenoid can fail electrically or become stuck due to contaminated fluid, triggering a P0700 and a specific solenoid code (e.g., P0750-P0770). This requires removing the transmission pan for diagnosis and replacement.
• Damaged Wiring Harness: The external wiring harness leading to the transmission can become damaged from road debris, heat, or corrosion, causing an open or short circuit for one of the sensors or solenoids. A visual inspection and continuity testing are necessary.
• Faulty Transmission Control Module (TCM): TCM failure is rare but possible. This should only be considered after all other possibilities, including sensors, wiring, fluid, and internal components, have been thoroughly ruled out. Sometimes a weak battery or poor ground connection can mimic TCM failure.

Diagnosis Steps

1. Connect an OBD-II scanner capable of reading transmission codes to the vehicle's diagnostic port.
2. Read codes from both the Engine Control Module (ECM) and the Transmission Control Module (TCM). The P0700 will be in the ECM. Note all codes stored in the TCM 🎬 Watch: Why your scanner might be missing the real problem., as they are the key to the diagnosis.
3. Prioritize diagnosis based on the specific TCM codes. For example, if P0705 is present, begin diagnosing the inhibitor switch. If P0711 is present, investigate the transmission temperature sensor circuit.
4. Check the transmission fluid level and condition. Low, burnt, or contaminated fluid can cause numerous problems.
5. Inspect the wiring harness and connectors going to the transmission for any visible damage, corrosion, or loose connections. Pay close attention to where the harness may rub against the chassis or engine components.
6. If a sensor is implicated (e.g., inhibitor switch, speed sensor), test the sensor's resistance and voltage according to the service manual specifications.
7. If a temperature sensor code (P0711-P0713) is present, use a scan tool to monitor the live data from the sensor to check for illogical or static readings.
8. If a solenoid code is present, the transmission pan will likely need to be removed to test the solenoid's resistance and function.
9. After replacing any parts, clear all codes from the ECM and TCM and perform a comprehensive test drive to ensure the problem is resolved.

Parts You'll Likely Need

• Inhibitor Switch (Neutral Safety Switch) (OEM #42700-26700) — This is a very common failure item that causes P0705 and triggers the P0700 code. It can lead to no-start conditions and erratic shifting.
  Trusted brands: Kia (Genuine), Hyundai (Genuine), Dorman, Standard Motor Products (SMP), Rostra Powertrain
• Output Speed Sensor — Failure is common and directly causes erratic shifting and speedometer issues, triggering a P0700.
  Trusted brands: Dorman (p/n 917-606), NTK, Carquest Premium, Standard Motor Products (SMP)
• Input Speed Sensor — Less common than the output sensor, but failure still leads to shifting problems and a P0700 code.
  Trusted brands: Dorman (p/n 917-607), NTK, Carquest Premium, SKP
• Internal Wire Harness (includes Temp Sensor) — The integrated temperature sensor is a known failure point on the 6-speed A6GF1 transmission, addressed by TSB TRANS 043. The entire harness must be replaced.
  Trusted brands: Kia (Genuine), Hyundai (Genuine)

Related Codes That Often Appear With This One

• P0705 — This code directly points to a malfunction in the Transmission Range Sensor (Inhibitor Switch) circuit, a very common cause for P0700 on this vehicle.
• P0720 — Indicates a malfunction with the Output Speed Sensor circuit, another frequent culprit that affects shifting and the speedometer.
• P0711, P0712, P0713 — These codes point to a problem with the Transmission Fluid Temperature Sensor circuit, which can cause erratic shifting and is addressed by TSB TRANS 043.
• P0717 — Indicates a fault with the Input Speed Sensor circuit, which can cause harsh or incorrect shifts.
• P0750-P0770 — This range of codes indicates faults with specific shift solenoids (A, B, C, etc.), pointing to an internal transmission hydraulic control issue.

Technical Service Bulletins (TSBs) & Recalls

• This TSB provides the procedure for replacing the transaxle oil temperature sensor for vehicles with a 6-speed automatic transmission that are logging DTCs P0711, P0712, or P0713. It explicitly states to replace the sensor and not the entire transaxle, and notes the repair can be done with the transaxle in the vehicle.
• Although for slightly later models (2017), this service action addresses inhibitor switch failures causing no-crank/no-start, erratic shifting, and P0705 codes. This indicates a known issue with the design/manufacturing of this component used across Kia models.
• A safety recall for 2010-2013 Fortes where the Air Bag Control Unit (ACU) can short circuit, preventing frontal airbags and seat belt pretensioners from deploying in a crash.
• A safety recall concerning an electrical short in the Hydraulic Electronic Control Unit (HECU), which can result in an engine compartment fire while parked or driving.
• These related bulletins describe a customer satisfaction program and extended warranty (10 years/unlimited miles) for the flexible steering coupler in the Motor Driven Power Steering (MDPS) system, which is known to degrade and cause a clicking or knocking noise when turning.

Mechanic-Grade Diagnostic Values

• A6GF1 On/Off Shift Solenoid Resistance — expected: 10 - 11 Ohms. Failure: A reading significantly higher (open) or lower (short) than the expected range.
• A6GF1 Variable Force Solenoid (VFS) Resistance — expected: ~5.1 Ohms. Failure: A reading significantly different from 5.1 Ohms indicates a faulty solenoid.
• Inhibitor Switch Power Supply Voltage — expected: Battery Voltage (approx. 12V) with Key On. Failure: No voltage or significantly low voltage indicates a problem with the power supply circuit or fuse (TCU2 fuse).
• Transmission Fluid Temperature (Live Data) — expected: Should start near ambient temperature and rise steadily to an operating temperature of ~122-140°F (50-60°C) or higher.. Failure: A static, unchanging value (e.g., -40°F or 212°F) or a value that does not rise with driving points to a failed sensor or circuit, as noted in TSB TRANS 043.

Scan Tool Commands That Help

• Kia GDS (Global Diagnostic System) / KDS: DTC Analysis — This is the primary function to read the specific, proprietary fault codes from the Transmission Control Module (TCM) that are causing the generic P0700 in the ECM.
• Kia GDS (Global Diagnostic System) / KDS: Data Analysis (Live Data) — Used to monitor live data streams from transmission sensors, such as the Oil Temperature Sensor, Input/Output Speed Sensors, and Inhibitor Switch position, to verify their operation in real-time.
• Kia GDS (Global Diagnostic System) / KDS: Resetting Auto Trans Adaptive Values — This function should be used after major transmission repairs, such as replacing the valve body or the entire transmission, to clear learned shift adaptations and force the TCM to relearn shift points with the new components.
• Kia GDS (Global Diagnostic System) / KDS: Actuation Test — Allows a technician to command individual shift solenoids to turn on or off while the vehicle is stationary to verify their electrical operation and listen for an audible click from the solenoid.

Wiring & Ground Locations

• Inhibitor Switch Connector — On the exterior of the transmission case, typically on the top or front, where the shift linkage connects.. This is the primary connection point for testing the inhibitor switch's power, ground, and signal outputs to the TCM. Corrosion or damage here is a common cause of P0705.
• TCM Connector — On some models, the TCM is integrated with the ECM in a single unit (PCM) located in the engine bay, often behind the battery. On others, it's a separate module. Schematics show it connecting to the engine fuse block via connectors like C102 and the main harness.. This is the termination point for all transmission sensor and solenoid wiring. Testing for continuity and voltage here can confirm if a wiring fault exists between a sensor and the control module.
• Rear Combination Lamp Harness Ground — In the trunk area, near the rear light assemblies.. Kia TSB TRA 055 identifies a poor ground at this location as a potential, and often overlooked, cause for inhibitor switch-related symptoms and codes. Checking and tightening this ground is a specific diagnostic step.
• TCU2 Fuse — Located in the engine room fuse box.. This fuse supplies power to the transmission control circuits. If it's blown, the TCM and inhibitor switch will not receive power, leading to a no-start condition and multiple transmission codes, including P0700.

Real Owner Repair Stories

• Reddit user in r/MechanicAdvice (2010 Kia Forte, 110k miles) — No reverse gear (engine just revs). When shifter is in Neutral, the car acts as if it's in Drive and moves forward. Drive works normally.
  ❌ Tried (didn't work) Checking transmission fluid level (was okay)., Manually moving the shift lever on the transmission itself, which produced the same result, ruling out a simple shifter linkage cable issue.
  ✅ What actually fixed it The user did not post a final fix, but the symptoms strongly pointed towards a severe internal transmission failure (e.g., failed clutch pack, valve body issue) rather than a simple sensor. The consensus was that the transmission likely needed a rebuild or replacement.

OEM Part Supersession History

• 42700-26500 (and others like 42700-26000) → 42700-26700 — Part has been updated and revised over time to improve reliability across multiple Hyundai/Kia platforms.
  Heads up: The newer part number 42700-26700 is the correct replacement for the older versions and is generally backward-compatible for this application.

Model Year Variations Within This Range

• 2010: Early 2010 models could be equipped with a 4-speed (A4CF2) or 5-speed automatic transmission. These use Kia ATF SP-III fluid. Their failure modes may differ slightly from the later 6-speed.
• 2011-2013: Most Fortes in this range came with the 6-speed automatic (A6GF1). This transmission is specifically mentioned in TSB TRANS 043 for temperature sensor/harness failure and uses Kia ATF SP-IV fluid. The shift solenoids have known resistance values of 10-11 ohms (on/off) and ~5.1 ohms (VFS).

Diagnostic Flowchart

Other Known Issues on This Vehicle

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

• Steering Coupler Disintegration 🟠 Medium — Extremely common. A clicking or knocking sound from the steering column when turning is the primary symptom. The rubber coupler degrades over time. (Ref: TSB CHA 044, Customer Satisfaction Program CS1604 (Warranty Extension))
• Engine Compartment Fire Risk 🔴 High — Subject to a major safety recall. An electrical short within the Hydraulic Electronic Control Unit (HECU) can cause a fire, even when the car is parked and off. (Ref: NHTSA Campaign 21V259000)
• Airbag Control Unit (ACU) Failure 🔴 High — Subject to a safety recall (SC165). The ACU can short circuit, preventing the airbags and seatbelt pretensioners from deploying in an accident. (Ref: Recall SC165)
• Brake Pedal Stopper Pad Deterioration 🟠 Medium — Common enough to warrant a safety recall (SC158). The plastic stopper pad disintegrates, which can cause the brake lights to stay on and may allow the vehicle to be shifted out of Park without depressing the brake pedal. (Ref: Recall SC158)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For externally mounted, easily accessible electronic parts like the inhibitor switch or the input/output speed sensors, a used part from a low-mileage donor vehicle can be a cost-effective option. These parts are typically plug-and-play and do not require programming.

Donor-vehicle mileage cap: roughly under 80000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• Check for a clean, corrosion-free connector.
• Inspect the part for any physical damage, cracks, or signs of extreme heat.
• If possible, ask for the VIN of the donor car to verify it had a clean history and was not involved in a flood.
• For sensors, test the resistance with a multimeter before purchase if the seller allows it.

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

• Internal Wire Harness (with Temperature Sensor): Given the labor involved in dropping the transmission pan, using a new OEM harness is strongly recommended to avoid a repeat failure. Aftermarket versions are rare and may not meet OEM quality standards for heat and fluid resistance.
• Transmission Control Module (TCM): A used TCM may not be compatible due to software differences and often requires dealer-level programming to the vehicle's VIN, making a new or professionally remanufactured unit a safer choice.

Aftermarket brands forum-validated for this vehicle:

• Inhibitor Switch: Standard Motor Products (SMP), Dorman, Rostra.
• Speed Sensors: Dorman, NTK, Carquest Premium.

Brands owners have reported issues with on this vehicle:

• Unbranded, no-name electronic sensors from online marketplaces can have high failure rates and may not have the correct resistance values, leading to persistent codes.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Documented NHTSA Reports

Related OBD-II Codes

• P0705 — Transmission Range Sensor Circuit Malfunction; triggered by a faulty inhibitor switch, which is a high-probability cause for P0700 in this vehicle.
• P0711 — Transmission Fluid Temperature Sensor Range/Performance; specifically addressed in Kia TSB TRANS 043 for the 6-speed automatic Forte.
• P0712 — Transmission Fluid Temperature Sensor Circuit Low; related to failures in the internal transmission wiring harness.
• P0713 — Transmission Fluid Temperature Sensor Circuit High; often occurs alongside P0700 when the TCM defaults to a safe temperature value of 176°F.
• P0717 — Input/Turbine Speed Sensor Circuit No Signal; one of the sensors subject to failure from heat and vibration in this model.
• P0720 — Output Speed Sensor Malfunction; a common failure that causes erratic speedometer operation and harsh shifting.
• P0721 — Output Speed Sensor Range/Performance; a companion code to P0700 indicating the TCM is receiving incorrect data for shift timing.

Frequently Asked Questions