P0037 on 2014-2019 Kia Soul: Causes and Fixes for O2 Sensor Heater Fault

What's Unique About the 2014-2019 Kia Soul

The P0037 code is a very common and straightforward issue on the second-generation Kia Soul. There are no unusual platform-specific defects that cause this code; it is typically the result of the oxygen sensor's internal heater simply wearing out after years of service. The repair is consistent across both the 1.6L and 2.0L engines 🎬 Watch: Diagnostic and replacement tips for Kia O2 sensors offered in this generation and its platform mates like the Hyundai Elantra and Kia Forte.

Symptoms You May Notice

• Check Engine Light (Malfunction Indicator Lamp) is on.
• Vehicle will fail an emissions test.
• Slightly decreased fuel economy (often not noticeable by the driver).
• In some rare cases, a rough idle may be noticed.

Most Likely Causes

1. Failed Downstream Oxygen Sensor 🔴 High Probability → Shop Oxygen Sensor The internal heater element within the sensor is a common failure point due to age and countless heat cycles. This is the most frequent cause for P0037 on this platform.
   How to confirm: Disconnect the sensor and measure the resistance between the two heater circuit wires (often the two wires of the same color) with a multimeter. An infinite resistance reading (open circuit) or a reading far outside the manufacturer's spec confirms the heater has failed.
   Typical fix: Replace the Bank 1, Sensor 2 oxygen sensor.
   Est. part cost: $50 - $120
2. Damaged Wiring or Connector 🟡 Medium Probability The wiring is routed near the hot exhaust system and under the vehicle, making it susceptible to melting, chafing, or corrosion over time. Damage from road debris is also possible.
   How to confirm: Visually inspect the wiring harness and connector leading to the downstream O2 sensor for any signs of melting, breaks, or corrosion in the pins. Check for secure connection.
   Typical fix: Repair the damaged section of the wire or replace the connector pigtail.
   Est. part cost: $10 - $30
3. Blown Fuse ⚪ Low Probability
   How to confirm: Locate the fuse for the O2 sensor heater circuit in the engine compartment fuse box. It is often a 10A or 15A fuse labeled 'SENSOR 1' or similar. Check for continuity.
   Typical fix: Replace the blown fuse. If it blows again, there is a short circuit in the wiring or the sensor itself that must be found and repaired.
   Est. part cost: $1 - $5

Rare But Worth Checking

• Faulty Engine Control Module (ECM): → Shop Engine Control Module (ECM) This is extremely rare. The ECM's internal driver for the heater circuit can fail, but this should only be considered after all other possibilities (sensor, wiring, fuse) have been definitively ruled out.

Diagnosis Steps

1. Retrieve the P0037 code using an OBD-II scanner.
2. Visually inspect the downstream oxygen sensor's wiring harness and connector for any obvious damage, such as melting on the exhaust pipe or frayed wires.
3. Locate and check the fuse associated with the oxygen sensor heater circuit, typically in the engine compartment fuse box and labeled 'SENSOR 1' (10A or 15A). Replace if blown.
4. If the wiring and fuse are intact, disconnect the oxygen sensor electrical connector.
5. Using a multimeter set to Ohms, measure the resistance between the two heater pins on the sensor side of the connector (usually the two same-colored wires). A reading of infinite resistance (OL) indicates a failed heater element, and the sensor needs replacement. Consult a service manual for the exact resistance specification, but a good heater is typically in the range of 5-20 Ohms.
6. If resistance is within specification, check for 12V power at the vehicle-side harness connector with the key on, engine off.
7. If power is missing, trace the circuit back to the fuse box to find the open or short. If power is present, check the ground/control side of the circuit for continuity back to the ECM.
8. If the sensor's heater has correct resistance and the wiring provides proper power and ground, the issue may be an intermittent connection or, in very rare cases, a faulty ECM.

Parts You'll Likely Need

• Downstream Oxygen Sensor (Bank 1, Sensor 2) (OEM #39210-2E200) — The internal heater element burning out is the most frequent cause of P0037. Always verify the part number with your vehicle's VIN before purchasing.
  Trusted brands: Denso, Bosch, NGK/NTK, Walker
  OEM price range: $110-$160
  Aftermarket price range: $50-$120

Platform-Specific Known Issues

• Seized O2 Sensor: → Shop Oxygen Sensor Due to its location in the exhaust stream, the downstream O2 sensor is highly prone to rusting and seizing in the exhaust pipe. Removal often requires significant force, a liberal application of penetrating oil (like PB Blaster) allowed to soak, and a specialized O2 sensor socket with a long breaker bar. Some owners have had to resort to heating the exhaust bung with a torch to break it free.

Mechanic-Grade Diagnostic Values

• Downstream O2 Sensor Heater Element Resistance — expected: Approximately 9.0 Ω at 68-70°F (20-21°C). A general acceptable range is often cited as 4-10 Ω.. Failure: A reading of infinite resistance (OL), near-zero ohms (short circuit), or a value significantly outside the expected range (e.g., 11.1 Ω or 14 Ω) indicates a failed heater element.
• Voltage at Heater Circuit Supply Pin (Harness Side) — expected: Battery voltage (approximately 11-13.5 Volts) with Key On, Engine Off (KOEO).. Failure: 0V or significantly low voltage points to a problem with the fuse, relay, or the power supply wire.

Scan Tool Commands That Help

• Kia GDS (Global Diagnostic System): DTC Analysis & Live Data (Sensors) — Used to view live data for the heater circuit duty cycle, follow guided diagnostic procedures from the manufacturer, and confirm voltage signals as seen by the ECM. This is most useful when basic multimeter tests are inconclusive or an intermittent fault is suspected.

Wiring & Ground Locations

• Downstream O2 Sensor Connector (2.0L Engine) — Inside the cabin, under the front passenger's seat carpet. The wire harness passes through a rubber grommet in the floor pan.. Knowing the connector is inside the vehicle is critical for DIY replacement on 2.0L models, as it requires removing interior trim to access, unlike the 1.6L model.
• Downstream O2 Sensor Connector (1.6L Engine) — In the engine bay, typically on a bracket at the back of the engine, below the upstream sensor's connector.. Access from the top of the engine makes diagnosis and replacement easier on the 1.6L models compared to the 2.0L.
• Heater Circuit Power and Ground Pins — At the sensor connector, the two heater wires are typically the same color (often both white).. Correctly identifying these two pins is essential for performing resistance and voltage tests with a multimeter to confirm the fault.

Real Owner Repair Stories

• Car Talk Community user 'Stinky1' (2014 Kia Soul, 126,xxx miles) — Check Engine Light with code P0141 (Heater Circuit Malfunction - functionally the same diagnosis as P0037).
  ✅ What actually fixed it The user tested the resistance of the downstream O2 sensor's heater circuit (across the two white wires) and got a reading of 11.1 ohms. The specified value was approximately 9.0 ohms. This deviation, although not an open circuit, was enough to confirm the sensor was out of spec and faulty. Replacing the sensor was the confirmed fix.

Model Year Variations Within This Range

• 2014-2019: The electrical connector for the downstream O2 sensor is in a different location depending on the engine. On 1.6L models, it is typically in the engine bay for easy access. On 2.0L models, the connector is often routed inside the cabin, under the passenger-side carpet, requiring interior trim removal for access.

Diagnostic Flowchart

Other Known Issues on This Vehicle

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

• Engine Failure / Excessive Oil Consumption (1.6L Gamma & 2.0L Nu) 🔴 High — Widespread issue across multiple model years, often appearing between 70,000 and 120,000 miles. Led to recalls and class-action lawsuits. (Ref: Multiple recalls (e.g., SC200, SC209) and campaigns (e.g., PI2107) were issued to install Knock Sensor Detection System (KSDS) software and inspect/replace engines due to piston ring and connecting rod bearing failures.)
• Degrading Flexible Steering Coupler 🟠 Medium — Extremely common. Owners typically notice a clicking or clunking noise from the steering column when turning, which worsens over time. (Ref: Kia issued TSB CHA-074 and extended the warranty for this part (56315-2K000-FFF) on earlier models, and the issue persists in this generation.)
• High Risk of Catalytic Converter Theft 🟠 Medium — The Kia Soul is frequently listed as one of the most targeted vehicles for catalytic converter theft nationwide due to its accessibility and the value of the metals.
• Steering Gear Pinion Separation 🔴 High — Less common than other issues but extremely dangerous, affecting certain 2014-2016 models. Can result in a complete loss of steering. (Ref: NHTSA #15V736000 / Kia Recall SC125 & SC155.)

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: Never. Oxygen sensors are wear-and-tear items with a finite lifespan, similar to spark plugs or brake pads. A used sensor from a junkyard has unknown remaining life and may fail shortly after installation, forcing you to do the job twice. The cost savings are not worth the risk and labor involved.

What to inspect on the donor part:

• Not applicable, as purchasing a used oxygen sensor is strongly discouraged.

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

• While not strictly OEM-only, it is critical to use a sensor from a reputable OE-supplier.

Aftermarket brands forum-validated for this vehicle:

• Bosch
• Denso
• NGK/NTK

Brands owners have reported issues with on this vehicle:

• Unbranded, no-name sensors from online marketplaces. These often have incorrect internal resistance values, leading to persistent check engine lights, or they fail very quickly.

Real Owner Stories

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

Related OBD-II Codes

• P0036 — A companion code for the Bank 1 Sensor 2 heater control circuit; often appears alongside or instead of P0037 when the heater element fails.
• P0137 — Secondary O2 sensor circuit low voltage; can appear with heater circuit issues if the sensor or wiring is damaged.
• P0420 — Catalytic converter efficiency code; related because the downstream O2 sensor (Sensor 2) is the component responsible for monitoring the catalyst's health.

Frequently Asked Questions