Can I drive with a P0155 code?

Yes. It mainly affects cold-start fuel economy and emissions, not safety or power. The car can be rejected at an emissions test while the code is set (rules vary by country), and a lit check engine light hides any new fault that appears later, so fix it at a convenient time.

Is P0155 the same as P0135?

It is the same fault on the other bank. P0135 is the heater circuit of the upstream sensor on bank 1, the bank with cylinder 1, and P0155 is the heater circuit of the upstream sensor on bank 2. If both appear together, check the shared heater fuse first.

How do you fix a P0155 code?

Check the heater fuse, then measure the sensor's heater resistance and check for battery voltage at its plug. If the fuse and supply are fine but the heater reads open, replace the bank 2 upstream sensor. Clear the code afterwards and confirm it stays off after a cold start.

Which sensor is Bank 2 Sensor 1?

It is the upstream oxygen sensor, the one before the catalytic converter, on the half of the engine that does not contain cylinder 1. Most V6, V8 and flat-six (boxer) engines have two cylinder banks, each with its own upstream sensor. A few inline-sixes with two exhaust manifolds, such as BMW's M54, also split into bank 1 (cylinders 1-3) and bank 2 (cylinders 4-6). Which physical side is bank 2 differs between makers, so check the service information for your engine before you order a part.

P0155: O2 Sensor Heater Circuit Malfunction (Bank 2, Sensor 1)

Quick Answer

Safe to drive (short-term)

P0155 means the internal heater of the upstream oxygen sensor on bank 2 has failed or lost its power or ground, so the sensor takes longer to reach working temperature after a cold start. Bank 2 is the half of a V6, V8 or flat-six engine that does not contain cylinder 1 (a few inline-sixes with a split exhaust, such as BMW's M54, also have one). It is the same fault as P0135 on the other bank. The usual cause is a burned-out heater inside the sensor, though a blown fuse or damaged wiring can do the same.

Severity: Low · Emissions
Estimated repair cost: From €1 to €320+, varies by vehicle

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What does P0155 mean?

P0155 is a emissions-related diagnostic trouble code classified as low severity. When your vehicle's ECU detects this condition, it stores P0155 and illuminates the check engine light.

Where it is on the car

Engine
Oxygen sensor before the converter (sensor 1)
Catalytic converter
Oxygen sensor after the converter (sensor 2, or 3 on some cars)
Silencer and tailpipe

This code is for bank 2. V6, V8 and flat engines have two cylinder banks, each with its own converter and sensors; bank 2 is the side without cylinder 1.

What are the symptoms of P0155?

If your vehicle has triggered P0155, you may notice one or more of these symptoms:

Check engine light on
Slightly worse fuel economy on cold starts and short trips
Engine takes longer to settle into normal fuel control after starting
Higher cold-start emissions, possible failed emissions test
No noticeable power loss once the engine is fully warm

What causes P0155?

Here are the most common causes of P0155:

Burned-out heater element inside the bank 2 upstream sensor
: high
Corroded, loose or heat-damaged connector or wiring at the bank 2 sensor
: medium
Blown O2 sensor heater fuse (often shared, so several heater codes appear together)
: medium
Failed heater relay or supply circuit
: low
Oil or coolant contamination baking onto the sensor and damaging the heater
: low
Faulty heater driver in the engine computer
: low

Is it safe to drive with P0155?

Generally yes, for short-term driving. Safe to drive. The sensor usually starts working once exhaust heat warms it, but until then bank 2 runs without mixture feedback, so fuel economy and emissions are worse on cold starts and short trips. Fix it before the next emissions test.

How do you diagnose P0155?

Follow these steps to pinpoint the root cause of P0155:

Read all stored codes. If other heater codes (P0135, P0141, P0161) are stored too, suspect a shared fuse, relay or wiring fault rather than one sensor
Check the O2 sensor heater fuse and replace it if blown, then find out why it blew before condemning the sensor
Unplug the bank 2 upstream sensor and measure resistance across its two heater pins. A healthy heater usually reads a few ohms; check the specification for your engine. An open circuit means the heater has burned out
With the key on, back-probe the harness plug and confirm battery voltage on the heater supply wire. No voltage points to a fuse, relay or wiring fault upstream of the sensor
Inspect the connector and the wiring run for corrosion, melted insulation and chafing against the exhaust
Replace the sensor if the heater reads open or out of range, clear the code and confirm it stays off after a cold start and warm-up

How much does P0155 cost to fix?

Repair costs for P0155 vary depending on the root cause and your vehicle. Here are typical estimates:

Repair	Parts Cost	Labor Cost	Total Estimate	DIY Difficulty
Replace O2 sensor heater fuse	€1–€5	€0–€30	€1–€35	Easy
Replace upstream O2 sensor (Bank 2, Sensor 1)	€40–€180	€50–€140	€90–€320	Moderate
Repair O2 sensor wiring or connector	€5–€25	€40–€120	€45–€145	Moderate

Prices estimated as of March 2026. Costs vary by region, vehicle, and shop.

Full repair guides

Oxygen Sensor Replacement Cost

P0155 on specific vehicles

P0155 behaves differently depending on your vehicle. Select your car below for model-specific causes and known issues:

P0155 on Mercedes-Benz

Mercedes-Benz C-Class (V6)

See Mercedes-Benz-specific causes & cost

P0155 on BMW

BMW 3 Series (E46 325i/330i)

See BMW-specific causes & cost

P0155 on Porsche

Porsche Boxster (986)

See Porsche-specific causes & cost

These codes are often seen alongside P0155 or indicate related issues:

Common questions about P0155

What does P0155 mean?: P0155 means the heater inside the upstream oxygen sensor on bank 2 is not working. The heater brings the sensor to working temperature within a short time of a cold start. Without it, the sensor waits for exhaust heat, so the engine runs longer without mixture feedback on that bank.
Can I drive with a P0155 code?: Yes. It mainly affects cold-start fuel economy and emissions, not safety or power. The car can be rejected at an emissions test while the code is set (rules vary by country), and a lit check engine light hides any new fault that appears later, so fix it at a convenient time.
Is P0155 the same as P0135?: It is the same fault on the other bank. P0135 is the heater circuit of the upstream sensor on bank 1, the bank with cylinder 1, and P0155 is the heater circuit of the upstream sensor on bank 2. If both appear together, check the shared heater fuse first.
How do you fix a P0155 code?: Check the heater fuse, then measure the sensor's heater resistance and check for battery voltage at its plug. If the fuse and supply are fine but the heater reads open, replace the bank 2 upstream sensor. Clear the code afterwards and confirm it stays off after a cold start.
Which sensor is Bank 2 Sensor 1?: It is the upstream oxygen sensor, the one before the catalytic converter, on the half of the engine that does not contain cylinder 1. Most V6, V8 and flat-six (boxer) engines have two cylinder banks, each with its own upstream sensor. A few inline-sixes with two exhaust manifolds, such as BMW's M54, also split into bank 1 (cylinders 1-3) and bank 2 (cylinders 4-6). Which physical side is bank 2 differs between makers, so check the service information for your engine before you order a part.

Read our detailed guides

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