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P0155 – Heated Oxygen Sensor (HO2S) Heater Performance (Bank 2 Sensor 1)

P0155 is a generic OBD-II Diagnostic Trouble Code (DTC) that indicates the Engine Control Module (ECM) has detected a malfunction in the heater circuit of the Heated Oxygen Sensor (HO2S) located at Bank 2 Sensor 1. This upstream oxygen sensor is installed before the catalytic converter on the engine bank that does not contain cylinder number one. The built-in heater allows the sensor to reach its operating temperature quickly, ensuring accurate fuel mixture control and reduced exhaust emissions. When the heater circuit fails to perform correctly, the ECM stores the P0155 code and illuminates the Check Engine Light.

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What Does P0155 Mean?

Bank 2 Sensor 1 is the upstream oxygen sensor positioned before the catalytic converter on the side of the engine opposite cylinder number one. The sensor's heater element is designed to warm the sensor rapidly after engine startup so the ECM can enter closed-loop operation sooner.

If the ECM detects that the heater circuit is open, shorted, or not operating within the specified range, it sets the P0155 diagnostic trouble code.

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Symptoms of P0155 Code

If your vehicle has a stored P0155 code, you may notice one or more of the following symptoms:

• Check Engine Light is ON
• Poor fuel economy
• Rough idle during cold starts

🔗 Related O2 Sensor Codes

P0135 | P0140 | P0150 | P0160

• Increased exhaust emissions
• Delayed closed-loop operation
• Slight loss of engine performance
• Failed emissions inspection

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Common Causes of P0155

Several issues can trigger the P0155 trouble code, including:

• Faulty Bank 2 Sensor 1 oxygen sensor
• Failed heater element inside the oxygen sensor
• Blown oxygen sensor heater fuse
• Damaged or melted wiring
• Loose or corroded electrical connector
• Open or short circuit in the heater circuit
• Poor ground connection
• Faulty Engine Control Module (ECM) (rare)

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How to Diagnose P0155

A proper diagnosis helps identify the exact cause of the problem.

Step 1: Confirm the Trouble Code

Connect an OBD-II scanner and verify the presence of the P0155 code. Check for any additional oxygen sensor or heater circuit-related codes.

Step 2: Inspect the Oxygen Sensor

Visually inspect the Bank 2 Sensor 1 oxygen sensor for physical damage, contamination, or signs of overheating.

Step 3: Inspect Wiring and Connector

Check the wiring harness and connector for broken wires, corrosion, melted insulation, loose terminals, or heat damage.

Step 4: Check the Heater Fuse

Inspect the oxygen sensor heater fuse and replace it if it is blown.

Step 5: Test the Heater Circuit

Use a digital multimeter to measure the resistance of the heater element and compare the reading with the manufacturer's specifications.

Step 6: Verify Power and Ground

Confirm that battery voltage reaches the heater circuit and verify a good ground connection.

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How to Fix P0155

Depending on the diagnosis, one or more of the following repairs may resolve the issue:

• Replace the faulty Bank 2 Sensor 1 oxygen sensor
• Repair damaged wiring or connectors
• Replace the blown heater fuse
• Repair an open or shorted heater circuit
• Clean corroded electrical terminals
• Clear the diagnostic code and perform a road test
• Replace the ECM only if all other components have been tested and verified

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Can You Drive with P0155?

Yes, the vehicle can usually still be driven for a short period. However, delaying repairs may reduce fuel efficiency, increase exhaust emissions, and prevent the engine from reaching closed-loop operation quickly. Prompt repair is recommended to maintain proper engine performance and emissions control.

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Estimated Repair Cost

Repair	Estimated Cost (USD)
Oxygen Sensor Replacement	$100 – $350
Wiring Repair	$50 – $250
Heater Fuse Replacement	$10 – $50
Electrical Connector Repair	$30 – $150
ECM Replacement (Rare)	$500 – $1,500

Repair costs may vary depending on the vehicle make, model, and local labor rates.

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Frequently Asked Questions (FAQs)

Is P0155 a serious trouble code?

P0155 is generally considered a moderate trouble code. While it may not immediately affect drivability, it can reduce fuel economy, increase emissions, and prevent the engine from operating efficiently during cold starts.

Can a faulty oxygen sensor cause P0155?

Yes. A failed heater element inside the Bank 2 Sensor 1 oxygen sensor is the most common cause of this code.

Can a blown fuse trigger P0155?

Yes. If the oxygen sensor heater fuse is blown, the heater circuit will stop working, causing the ECM to store the P0155 code.

Will replacing the oxygen sensor always fix P0155?

Not always. Wiring damage, blown fuses, poor electrical connections, or heater circuit faults should also be inspected before replacing the sensor.

How long does it take to replace an oxygen sensor?

Replacing an upstream oxygen sensor typically takes 30 to 60 minutes, depending on the vehicle model and sensor location.

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Preventive Maintenance Tips

To reduce the chances of the P0155 code returning:

• Replace oxygen sensors at the recommended maintenance interval.
• Inspect wiring and connectors during routine service.
• Repair exhaust leaks promptly.
• Keep the battery and charging system in good condition.
• Use high-quality OEM or equivalent replacement oxygen sensors.
• Protect wiring from excessive engine heat.

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Conclusion

The P0155 – Heated Oxygen Sensor (HO2S) Heater Performance (Bank 2 Sensor 1) trouble code indicates that the heater circuit of the upstream oxygen sensor is not operating correctly. Common causes include a faulty oxygen sensor, damaged wiring, a blown fuse, or an open heater circuit. Diagnosing and repairing the problem early helps improve fuel economy, reduce emissions, ensure faster closed-loop operation, and maintain reliable engine performance.