A faulty downstream oxygen sensor heater element (open circuit or high resistance inside the sensor).; Damaged or corroded wiring or connector at the sensor, especially at the heater circuit pins.; Blown fuse or relay that supplies power to the oxygen sensor heater circuit.; Open or shorted wire between the sensor and the engine computer, often due to chafing or heat damage.; Poor ground connection for the heater circuit, causing low current flow.; Engine computer internal fault, though this is rare and should be considered only after all other causes are ruled out.

DTC codes / P00xx · Fuel and air metering and auxiliary emission controls / P0037

P0037HO2S Heater Control Circuit Low (Bank 1 Sensor 2)

Q: What does code P0037 mean?

HO2S Heater Control Circuit Low (Bank 1 Sensor 2). P0037 means the engine computer has detected that the heater circuit inside the downstream oxygen sensor (Bank 1 Sensor 2) is drawing less current than expected when the heater is commanded on. The sensor's built-in heater is not getting enough voltage or current, so the sensor may not reach operating temperature quickly enough for accurate emissions monitoring.

P0037 means the engine computer has detected that the heater circuit inside the downstream oxygen sensor (Bank 1 Sensor 2) is drawing less current than expected when the heater is commanded on. The sensor's built-in heater is not getting enough voltage or current, so the sensor may not reach operating temperature quickly enough for accurate emissions monitoring.

SystemPowertrain

Code typeGeneric (all makes)

SeverityLow

Fix difficultyIntermediate

AreaFuel and air metering and auxiliary emission controls

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms.
A slight decrease in fuel economy if the sensor stays cold and the computer runs a richer default mixture.
Occasional rough idle or hesitation when the engine is cold, though this is less common.
Failed emissions inspection due to the stored code and incomplete readiness monitors.
In rare cases, a noticeable delay in the oxygen sensor's response, leading to sluggish engine performance.

Common causes, most likely first

A faulty downstream oxygen sensor heater element (open circuit or high resistance inside the sensor).
Damaged or corroded wiring or connector at the sensor, especially at the heater circuit pins.
Blown fuse or relay that supplies power to the oxygen sensor heater circuit.
Open or shorted wire between the sensor and the engine computer, often due to chafing or heat damage.
Poor ground connection for the heater circuit, causing low current flow.
Engine computer internal fault, though this is rare and should be considered only after all other causes are ruled out.

How to diagnose and fix it

Check the fuse and relay for the oxygen sensor heater circuit and replace if blown or faulty.
Inspect the sensor connector and wiring for corrosion, damage, or loose pins; clean or repair as needed.
Measure the resistance of the heater element at the sensor connector with a multimeter and compare to specification.
Check for voltage at the heater supply wire with the key on and engine off; repair open or short circuits as necessary.
Test the ground circuit for the heater using a voltage drop test; repair poor grounds.
If all electrical checks pass, replace the downstream oxygen sensor with a quality direct-fit unit.
Clear the code and verify the repair by running the engine and confirming the heater circuit operates correctly with a scan tool.

Don't overlook the heater fuse and ground

A blown fuse for the oxygen sensor heater is a common cause of P0037 that many people miss because they replace the sensor first.
The downstream sensor's heater is often on the same circuit as other components, so a shared fuse or relay failure can set this code.
Corrosion inside the sensor connector can increase resistance and trigger P0037 even if the sensor itself is good.
A faulty ground connection can cause low current flow in the heater circuit, mimicking a failed sensor.
P0037 does not always mean the sensor is completely dead; it may still function but not heat up quickly enough, affecting emissions.

Can I keep driving with P0037?

You can generally continue driving with P0037 because the downstream sensor's heater is mainly for emissions control and does not affect engine safety. However, avoid long periods of idling or short trips that prevent the sensor from warming up, and get it diagnosed soon to ensure your vehicle passes emissions testing.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.