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P0038 Code Explained: HO2S Heater Control Circuit High Bank 1 Sensor 2 Causes, Symptoms & Fixes

OBD-II scanner displaying P0038 beside a downstream heated oxygen sensor located after the catalytic converter with the heater wiring and connector highlighted.

If your OBD-II scanner displays P0038, 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 above its expected voltage range.

The generic SAE definition for P0038 is:

HO2S Heater Control Circuit High Bank 1 Sensor 2

Unlike P0036, which indicates a general heater circuit malfunction, or P0037, which indicates a low-voltage condition, P0038 specifically means the ECM has detected excessive voltage or insufficient current flow in the heater circuit for the downstream oxygen sensor.

Depending on the manufacturer, the affected sensor may also be referred to as the:

The internal heater allows the oxygen sensor to reach operating temperature quickly after startup. When the ECM detects an open circuit, excessive resistance, or another condition causing higher-than-expected voltage in the heater circuit, it stores P0038.

Common causes include:

Unlike upstream oxygen sensor heater codes, P0038 typically has little effect on engine performance but can prevent emissions monitors from completing and cause an emissions inspection failure.

For more diagnostic resources, visit:

P0038 Quick Facts

ItemInformation
OBD-II CodeP0038
DescriptionHO2S Heater Control Circuit High Bank 1 Sensor 2
CategoryPowertrain
SystemHeated Oxygen Sensor
SensorBank 1 Sensor 2
Sensor LocationDownstream (After Catalytic Converter)
SeverityLow to Moderate
Safe to Drive?Yes
Typical Repair Cost$100–700+

What Does P0038 Mean?

P0038 indicates that the ECM has detected a high-voltage condition in the heater circuit for the downstream oxygen sensor located on Bank 1.

Most manufacturers interpret a Circuit High condition as:

When current flow becomes too low, voltage remains higher than expected and the ECM stores P0038.

Unlike upstream oxygen sensors, Bank 1 Sensor 2 is primarily responsible for monitoring catalytic converter efficiency, not controlling fuel mixture.

What Is Bank 1 Sensor 2?

Understanding oxygen sensor locations is essential.

Bank 1

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

Inline engines have only Bank 1.

V-type engines have:

Sensor 2

Sensor 2 is always the downstream oxygen sensor.

It is mounted:

Its primary responsibility is monitoring catalytic converter performance rather than adjusting air-fuel ratio.

What Does the Oxygen Sensor Heater Do?

The downstream oxygen sensor contains an electric heater that quickly raises the sensing element to operating temperature.

This allows the ECM to:

Without the heater, the sensor may require several minutes before becoming active.

Why Does the Downstream Sensor Need a Heater?

Although the downstream sensor doesn’t actively control fuel delivery, it must still become operational quickly to:

The heater dramatically shortens warm-up time.

How the ECM Detects P0038

The ECM continuously monitors:

P0038 may be stored if:

P0036 vs P0037 vs P0038

These three codes diagnose the same downstream oxygen sensor heater circuit.

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 P0038

Common symptoms include:

Most drivers experience little or no noticeable drivability symptoms.

Common Causes of P0038

1. Open Heater Element

The heater inside the oxygen sensor burns open over time.

This is the most common cause.

2. Open Wiring

Broken wiring may result from:

3. Broken Power Wire

The heater loses battery voltage due to:

4. Corroded Connector

Corrosion increases circuit resistance.

Inspect for:

5. Loose Connector

Inspect for:

6. Melted Wiring

The downstream oxygen sensor operates near:

High temperatures may damage the wiring harness.

7. Blown Heater Fuse

Some manufacturers use shared oxygen sensor heater fuses.

Always test the fuse electrically.

8. Failed Heater Relay

A faulty relay may interrupt power to the heater.

9. Incorrect Replacement Oxygen Sensor

Aftermarket sensors with incorrect heater resistance may trigger P0038.

Always verify the correct part number.

10. High Resistance

High resistance may develop because of:

11. Damaged Wiring Harness

Inspect for:

12. ECM Driver Failure

Although rare, the ECM output driver may fail internally.

Always eliminate wiring faults before replacing the ECM.

Is P0038 Serious?

Generally Low to Moderate.

Unlike upstream heater faults, P0038 usually has minimal effect on engine operation.

However, it may:

Can You Drive With P0038?

Yes.

Most vehicles remain fully driveable.

Repair should still be completed before emissions testing.

How to Diagnose P0038

Step 1

Scan for additional trouble 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.

Check for:

Step 4

Inspect wiring.

Pay particular attention to wiring near:

Step 5

Check the heater fuse.

Test using a multimeter.

Never rely solely on visual inspection.

Step 6

Measure heater resistance.

Infinite resistance usually indicates an open heater element.

Step 7

Verify power supply.

Battery voltage should be present when the heater is commanded on.

Step 8

Check the control circuit.

Inspect for:

Step 9

Perform voltage-drop testing.

Inspect:

Step 10

Command the heater with a bidirectional scan tool.

Verify:

Step 11

Check Technical Service Bulletins.

Some manufacturers have released updated oxygen sensors or revised harness routing.

Step 12

Verify repair.

After repairs:

  1. Clear codes.
  2. Cold start the engine.
  3. Complete a drive cycle.
  4. Verify catalyst readiness completes.
  5. Confirm P0038 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

P0038 may appear on nearly any OBD-II vehicle equipped with heated oxygen sensors, including:

How to Prevent P0038

Reduce the likelihood of P0038 by:

Frequently Asked Questions

What does P0038 mean?

P0038 indicates a high-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 P0038?

Yes.

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

Can wiring cause P0038?

Absolutely.

Broken wiring and excessive resistance frequently trigger this code.

Will P0038 affect engine performance?

Usually not.

Most vehicles continue to run normally.

Can I drive with P0038?

Yes.

However, emissions readiness monitors may not complete.

Will P0038 fail emissions?

Yes.

An active Check Engine Light or incomplete readiness monitors generally result in an emissions inspection failure.

Will replacing the catalytic converter fix P0038?

No.

P0038 is a heater circuit fault, not a catalytic converter failure.

Final Thoughts

The P0038 code indicates the ECM has detected a high-voltage condition in the heater circuit for the downstream oxygen sensor (Bank 1 Sensor 2). In most cases, the problem is caused by an open heater element, broken wiring, excessive circuit resistance, or poor electrical connections rather than a faulty catalytic converter.

Begin diagnosis by verifying the correct oxygen sensor location, inspecting the wiring near the catalytic converter, measuring heater resistance, checking power and ground, and testing the heater circuit before replacing expensive components.

Related Articles

Continue diagnosing oxygen sensor and emissions-related problems with these Pro Street guides:

Upstream Oxygen Sensor Heater Codes

Downstream Oxygen Sensor Heater Codes

Browse our complete diagnostic libraries:

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