P0037 on 2011-2016 Scion tC: O2 Sensor Heater Circuit Causes and Fixes

What's Unique About the 2011-2016 Scion tC

The 2011-2016 Scion tC uses the reliable Toyota 2AR-FE engine, which has a straightforward emissions system. Since it's an inline 4-cylinder, there is only one exhaust bank, making component location simple. For Toyota-family vehicles like Scion, using an OEM or a reputable OEM-supplier brand like Denso for replacement sensors is highly recommended to ensure compatibility and avoid recurring issues, a point frequently emphasized by owners in forums.

Symptoms You May Notice

• Check Engine Light is on
• Failure to pass an emissions inspection
• Slightly reduced fuel economy
• Rough idle or hesitation (less common)

Most Likely Causes

1. Failed Downstream Oxygen Sensor (Bank 1, Sensor 2) 🔴 High Probability → Shop Oxygen Sensor The internal heater element of the sensor is a common failure point over time due to constant heat cycles. This is the most frequent cause for P0037 on this platform.
   How to confirm: Using a multimeter, measure the resistance between the two heater circuit pins on the sensor's connector (often two black or two white wires). A good sensor should have a specific resistance, typically between 5 and 15 ohms when cold. An open circuit (infinite resistance or 'OL') or a reading far from spec confirms the heater has failed.
   Typical fix: Replace the downstream oxygen sensor. 🎬 Watch: This walkthrough shows how to replace the sensor. This sensor is located on the exhaust pipe after the catalytic converter. Torque the new sensor to approximately 22 ft-lbs (30 Nm).
   Est. part cost: $60 - $170
2. Damaged Wiring or Connector 🟡 Medium Probability The wiring harness is located under the vehicle and near the hot exhaust, making it susceptible to heat damage, corrosion, or physical damage from road debris. Water intrusion into the connector after an engine wash has also been reported as a cause.
   How to confirm: Visually inspect the wiring harness and connector leading to the sensor for any signs of melting, chafing, corrosion, or broken wires. Check for 12V power at the harness-side connector with the ignition on.
   Typical fix: Repair the damaged section of the wiring harness or replace the connector pigtail.
   Est. part cost: $10 - $40
3. Blown Fuse ⚪ Low Probability
   How to confirm: Check the fuse box in the engine bay for a blown fuse. It is often a 15A or 20A fuse labeled 'A/F HEATER' or 'EFI NO. 1'. If the fuse is blown, it may indicate a short in the circuit that needs to be found.
   Typical fix: Replace the blown fuse. If it blows again, a short circuit exists in the wiring or the sensor itself and must be diagnosed.
   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. All other possibilities, especially the sensor and wiring, should be exhaustively ruled out before considering the ECM as the cause.

Diagnosis Steps

1. Read the code with an OBD-II scanner to confirm P0037 is the only code present.
2. Locate the fuse box in the engine compartment and inspect the fuse for the oxygen sensor heater circuit (often labeled 'A/F HEATER'). Replace if blown.
3. Safely raise and support the vehicle to access the exhaust system.
4. Locate the downstream oxygen sensor (Bank 1, Sensor 2) on the exhaust pipe, following the catalytic converter.
5. Visually inspect the sensor's connector and wiring harness for any signs of melting, fraying, water intrusion, or physical damage.
6. Disconnect the sensor. With the ignition on (engine off), use a multimeter to test for 12-volt power on the harness side of the connector.
7. Test the sensor itself. Measure the resistance across the two heater pins on the sensor's connector (typically the two same-colored wires). A reading of 'OL' (open circuit) confirms a failed heater. A good sensor should read between 5-15 ohms at ambient temperature.
8. If wiring and fuses are good, but the sensor's heater resistance is out of spec, the sensor is faulty and needs replacement.
9. When installing the new sensor, apply anti-seize to the threads if not pre-applied and torque to approximately 22 ft-lbs (30 Nm).

Parts You'll Likely Need

• Downstream Oxygen Sensor (Bank 1, Sensor 2) (OEM #89465-21060 (for 2011-2014 models)) — This is the component that contains the heater element reported as faulty by the P0037 code. Its internal heater is the most common failure point.
  Trusted brands: Denso (OEM Supplier), NGK, Bosch
  OEM price range: $120-$170
  Aftermarket price range: $60-$90

Platform-Specific Known Issues

• Sensitivity to Aftermarket Sensors: Owners on forums strongly advise using a genuine Toyota or Denso-branded replacement sensor. Using other brands, even reputable ones like Bosch, has been reported to cause the P0037 code to return shortly after replacement. Sticking with the OEM supplier (Denso) is the safest bet for a one-time fix.

Mechanic-Grade Diagnostic Values

• Downstream O2 Sensor (B1S2) Heater Resistance — expected: 5.0 to 15.0 Ohms at ambient temperature.. Failure: A reading of OL (Open Loop/infinite resistance) or a value significantly outside the specified range indicates a failed heater element.
• ECM Heater Circuit Current Draw — expected: Greater than 0.3 Amps.. Failure: If the ECM detects the heater current is less than 0.3 Amps, it will set DTC P0037.
• Voltage at Harness Connector (Heater Power Pin) — expected: Approximately 12V (Battery Voltage) with ignition ON, engine OFF.. Failure: Significantly lower or no voltage suggests a problem with the fuse or wiring leading to the sensor.

Scan Tool Commands That Help

• Toyota Techstream: Active Test: "Control the A/F Sensor Heater" or similar function. — This allows a technician to manually command the O2 sensor heater circuit ON and OFF. By observing live data for heater voltage and current during the test, a technician can confirm if the ECM driver is functioning and if the circuit responds as expected, helping to differentiate between a sensor, wiring, or ECM fault.

Wiring & Ground Locations

• B1, B2 — Front of the engine.. These are primary ground points for the engine harness. A corroded or loose ground at these locations can cause various electrical issues, including erratic sensor readings or faults in the O2 sensor heater circuit.
• Heated Oxygen Sensor (Bank 1 Sensor 2) Connector — Under the vehicle, on the exhaust pipe after the catalytic converter, connecting the sensor to the main engine harness.. This is the primary point of failure for wiring issues due to its exposure to heat, moisture, and road debris. The heater circuit wires are typically the two same-colored wires (e.g., two black or two white) in the 4-wire connector.

OEM Part Supersession History

• 89465-21060 → 89465-21061 — Standard part revision by the manufacturer.
  Heads up: Part 89465-21060 is specified for models up to 05/2013 or 2014, while later models may use a different part number. Always verify the part number with the vehicle's VIN.

Model Year Variations Within This Range

• 2014-2016: The Scion tC received a facelift for the 2014 model year. While the core engine (2AR-FE) and exhaust layout remained the same, there were minor changes to suspension and automatic transmission logic. The O2 sensor part number may differ for post-facelift models, with the original part 89465-21060 listed for 2011-2014 models. It is critical to verify the correct part number via VIN for 2014-2016 vehicles.

Diagnostic Flowchart

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: For this repair, buying a used part is generally not recommended. The primary failure is the O2 sensor itself, which is a wear-and-tear item. A used sensor has unknown remaining life and may fail soon after installation. A used wiring harness pigtail from a junkyard could be a cost-effective option if only the connector is damaged.

Donor-vehicle mileage cap: roughly under 50000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• For a connector pigtail, inspect for any signs of melting, brittleness, or corrosion on the pins.
• Ensure the locking tab on the connector is intact.
• Check that the wires have sufficient length for splicing and show no signs of fraying or heat damage.

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

• Oxygen Sensor

Aftermarket brands forum-validated for this vehicle:

• Denso (OEM supplier)
• NGK/NTK

Brands owners have reported issues with on this vehicle:

• Generic, unbranded, or 'white-box' sensors from online marketplaces are frequently reported to be incompatible or fail prematurely, causing the code to return.

Real Owner Stories

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

Related OBD-II Codes

• P0038 — This is the direct counterpart to P0037, indicating a 'High' circuit condition for the same Bank 1, Sensor 2 heater. Both codes point to the same set of potential failures: the sensor, wiring, or fuse.
• P0137 — O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2). This code relates to the signal from the same sensor, not its heater. An owner reported seeing this code alongside P0037 initially, suggesting a comprehensive failure of the sensor unit.
• P0138 — O2 Sensor Circuit High Voltage (Bank 1 Sensor 2). Similar to P0137, this code points to a signal fault in the same physical sensor. It can appear with P0037 if the sensor has multiple internal failures.
• P0606 — ECM/PCM Processor Fault. In one owner report, this code appeared with the initial O2 sensor faults before being cleared, leaving only P0037. It can be a temporary companion code during a circuit fault.
• P0420 — Catalyst System Efficiency Below Threshold. The downstream O2 sensor (implicated in P0037) is what monitors the catalytic converter. A faulty heater prevents the sensor from working correctly, which can mask or be related to a P0420 code.

Frequently Asked Questions