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P0037 Code Explained: HO2S Heater Control Circuit Low Bank 1 Sensor 2 Causes, Symptoms & Fixes

OBD-II scanner displaying P0037 beside a downstream heated oxygen sensor mounted behind the catalytic converter with the heater wiring highlighted.

If your OBD-II scanner displays P0037, your vehicle’s Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected that the heater control circuit for the Bank 1 Sensor 2 heated oxygen sensor (HO2S) is operating below its expected voltage range.

The generic SAE definition for P0037 is:

HO2S Heater Control Circuit Low Bank 1 Sensor 2

Unlike P0036, which indicates a general heater circuit malfunction, P0037 specifically means the ECM has detected a low-voltage or excessive-current condition in the heater circuit for the downstream oxygen sensor.

Depending on the manufacturer, Bank 1 Sensor 2 may also be referred to as the:

The heater inside the oxygen sensor allows it to reach operating temperature much faster after startup. When the ECM detects abnormal electrical characteristics—such as excessive current draw or low circuit voltage—it stores diagnostic trouble code P0037.

Common causes include:

Although P0037 usually does not cause severe drivability problems, it can prevent emissions readiness monitors from completing and may cause your vehicle to fail an emissions inspection.

For additional troubleshooting information, browse our diagnostic libraries:

P0037 Quick Facts

ItemInformation
OBD-II CodeP0037
DescriptionHO2S Heater Control Circuit Low Bank 1 Sensor 2
CategoryPowertrain
SystemHeated Oxygen Sensor
SensorBank 1 Sensor 2
LocationDownstream (After Catalytic Converter)
SeverityLow to Moderate
Safe to Drive?Usually Yes
Typical Repair Cost$100–700+

What Does P0037 Mean?

P0037 indicates that the ECM has detected a low-voltage condition in the heater circuit of the downstream oxygen sensor located on Bank 1.

Most manufacturers interpret a “Circuit Low” condition as:

The ECM continuously monitors:

If current exceeds calibrated limits or voltage falls below specifications, P0037 is stored.

What Is Bank 1 Sensor 2?

Understanding oxygen sensor locations makes diagnosing this code much easier.

Bank 1

Bank 1 is the side of the engine containing cylinder number one.

Inline engines have only Bank 1.

V6, V8 and flat engines typically have:

Sensor 2

Sensor 2 is always the downstream oxygen sensor.

It is installed:

Unlike the upstream oxygen sensor, Sensor 2 primarily monitors catalytic converter efficiency rather than controlling fuel mixture.

What Does the Oxygen Sensor Heater Do?

The oxygen sensor contains an internal heating element that rapidly warms the sensing element after startup.

Benefits include:

Without the heater, the downstream sensor may require several minutes before it begins operating correctly.

Why Does the Downstream Sensor Have a Heater?

Although the downstream sensor doesn’t directly control air-fuel mixture, it must still reach operating temperature quickly to monitor catalytic converter efficiency.

The heater helps the ECM:

How the ECM Detects P0037

The ECM monitors:

P0037 may be stored if:

P0036 vs P0037 vs P0038

These three codes all diagnose the downstream oxygen sensor heater.

CodeDescription
P0036HO2S Heater Control Circuit Bank 1 Sensor 2
P0037HO2S Heater Control Circuit Low Bank 1 Sensor 2
P0038HO2S Heater Control Circuit High Bank 1 Sensor 2

Generally:

Symptoms of P0037

Common symptoms include:

Most drivers notice no change in engine performance.

Common Causes of P0037

1. Shorted Oxygen Sensor Heater

The heater element may internally short.

This is one of the most common causes.

2. Short to Ground

The heater wiring may contact:

Resulting in excessive current draw.

3. Melted Wiring

The downstream oxygen sensor is exposed to high exhaust temperatures.

Harness insulation may melt against:

4. Damaged Connector

Inspect for:

5. Corroded Connector

Moisture intrusion may create:

6. Water Intrusion

Water entering the connector may short adjacent terminals together.

7. Incorrect Replacement Sensor

Incorrect sensors may have:

Always use a direct-fit OEM-quality replacement.

8. Blown Heater Fuse

Some vehicles share heater circuits among multiple oxygen sensors.

Always verify fuse condition using a multimeter.

9. Failed Heater Relay

Some manufacturers use a dedicated relay to power oxygen sensor heaters.

10. Damaged Wiring Harness

Inspect for:

11. Poor Ground

Excessive ground resistance may affect heater operation.

Perform voltage-drop testing.

12. ECM Driver Failure

Although uncommon, the ECM’s internal heater driver may short internally.

Only suspect ECM failure after eliminating wiring faults.

Is P0037 Serious?

Generally Low to Moderate.

The vehicle usually remains completely driveable.

However, prolonged operation may result in:

Can You Drive With P0037?

Yes.

Most vehicles drive normally.

Repairs should still be completed before emissions testing.

How to Diagnose P0037

Step 1

Scan for additional codes.

Related codes include:

Step 2

Confirm Bank 1 Sensor 2 location.

Verify the sensor is installed after the catalytic converter.

Step 3

Inspect the connector.

Look for:

Step 4

Inspect the wiring harness.

Pay close attention to wiring routed near:

Step 5

Check the heater fuse.

Test electrically rather than visually.

Step 6

Measure heater resistance.

Low resistance typically indicates an internally shorted heater.

Step 7

Check for a short to ground.

Inspect both heater wires carefully.

Step 8

Verify power supply.

Confirm battery voltage reaches the heater connector.

Step 9

Perform voltage-drop testing.

Inspect:

Step 10

Command the heater using a bidirectional scan tool.

Monitor:

Step 11

Check Technical Service Bulletins.

Some manufacturers have updated oxygen sensors or revised harness routing.

Step 12

Verify repair.

After repairs:

  1. Clear codes.
  2. Perform a cold start.
  3. Complete a drive cycle.
  4. Verify readiness monitors complete.
  5. Confirm P0037 does not return.

Common Repairs

RepairEstimated Cost
Heater fuse replacement$10–50
Wiring repair$100–400
Connector replacement$75–250
Downstream oxygen sensor replacement$180–550
Heater relay replacement$80–200
ECM programming$100–300
ECM replacement$1,000–2,500

Common Diagnostic Mistakes

Vehicles Commonly Affected

P0037 may appear on virtually any OBD-II vehicle equipped with heated oxygen sensors, including:

How to Prevent P0037

Reduce the likelihood of P0037 by:

Frequently Asked Questions

What does P0037 mean?

P0037 indicates the ECM has detected a low-voltage condition in the heater circuit for the Bank 1 Sensor 2 oxygen sensor.

Where is Bank 1 Sensor 2 located?

After the catalytic converter on the engine bank containing cylinder number one.

Can a bad oxygen sensor cause P0037?

Yes.

An internally shorted heater element is one of the most common causes.

Can wiring cause P0037?

Absolutely.

Heat-damaged wiring is frequently responsible.

Will P0037 affect engine performance?

Usually not.

Most vehicles drive normally.

Can I drive with P0037?

Yes.

However, emissions readiness monitors may not complete.

Will P0037 fail emissions?

Yes.

A Check Engine Light or incomplete readiness monitors generally cause an emissions inspection failure.

Will replacing the catalytic converter fix P0037?

No.

P0037 is an electrical heater circuit fault rather than a catalyst failure.

Final Thoughts

The P0037 code indicates the ECM has detected a low-voltage condition in the heater circuit for the downstream oxygen sensor (Bank 1 Sensor 2). The problem is most commonly caused by a shorted heater element, melted wiring near the exhaust, damaged connectors, or a short to ground.

Start diagnosis by confirming the correct oxygen sensor, inspecting the wiring around the catalytic converter, measuring heater resistance, and checking for shorts before replacing any components. In most cases, replacing the downstream oxygen sensor or repairing damaged wiring resolves the issue.

Related Articles

Continue diagnosing oxygen sensor and emissions-related faults with these guides already published on Pro Street:

Upstream Oxygen Sensor Heater Codes

Downstream Oxygen Sensor Heater Codes

You can also browse the complete diagnostic libraries:

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