What does code P0135 mean?

P0135 means the heater circuit in the Bank 1, Sensor 1 oxygen sensor (the upstream, pre-catalyst sensor) is not working correctly. The internal heater that brings the sensor up to operating temperature has failed or lost power, so the sensor warms slowly and the engine takes longer to enter closed-loop fuel control.

What causes a P0135 code?

The most common cause is a failed heater element inside the upstream oxygen sensor from normal wear with age and mileage. Other causes include a blown shared heater fuse (which usually trips several heater codes at once), corroded or damaged wiring and connectors, a faulty heater relay, or oil and coolant contamination baking onto the sensor.

Is it safe to drive with a P0135 code?

Yes, it is generally safe to drive in the short term. The engine still runs and the fault mostly affects cold-start fuel economy and emissions, not safety. A lit check engine light can get the car rejected at an emissions test, so fix it promptly. Driving on a check engine light also masks any new fault that appears later.

How do you fix and clear a P0135 code?

First check the heater fuse, then measure the sensor's heater resistance (about 2-15 ohms is healthy) and inspect the connector and wiring. If the heater reads open or out of range, replace the Bank 1, Sensor 1 oxygen sensor. After the repair, clear the code with a scan tool and drive through a warm-up cycle to confirm it does not return.

How much does it cost to fix P0135, and which sensor is it?

P0135 refers to Bank 1, Sensor 1, the upstream sensor before the catalytic converter on the cylinder bank that contains cylinder 1. A replacement upstream oxygen sensor typically costs 100 to 300 EUR including labour, with OEM-quality sensors up to about 400 EUR. If the fault is only a blown fuse, the fix can cost just a few euros.

Is P0135 worse than P0141?

Slightly. P0135 is the upstream (pre-catalyst) sensor, which directly controls fuel delivery, so until the heater warms it the ECU runs open-loop on a richer mixture. P0141 is the downstream monitor sensor and costs you nothing but the warning light. Both are safe to drive with, but P0135 hurts cold-start fuel economy on short trips.

Can P0135 cause P0171 or P0172?

Indirectly. While the heater should be working but is not, the ECU stays in open loop and may run richer than needed, which can set a fuel-trim code. If P0171 or P0172 appears alongside P0135, fix the heater fault first and see whether the trim code clears once closed-loop control is restored.

P0135: O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)

Quick Answer

Safe to drive (short-term)

P0135 means the internal heater element of your upstream (Bank 1, Sensor 1) oxygen sensor has failed, so the sensor warms up too slowly and the engine delays entering closed-loop fuel control. The most common cause is simple heater wear inside the sensor. Because this pre-catalyst sensor sets the air-fuel mixture, you mainly notice a check engine light and worse cold-start fuel economy. A replacement upstream O2 sensor costs roughly 100 to 300 EUR including labour, or up to about 400 EUR with an OEM-quality part.

Severity: Low · Emissions
Estimated repair cost: From €1 to €400+, varies by vehicle

Scan your own car in about 60 seconds: see whether P0135 is really what it has, how urgent it is, and what the fix should cost. Free on iPhone and Android with an ELM327 adapter (Bluetooth LE on iPhone).

Get Skanyx free

What does P0135 mean?

P0135 is a emissions-related diagnostic trouble code classified as low severity. When your vehicle's ECU detects this condition, it stores P0135 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

What are the symptoms of P0135?

If your vehicle has triggered P0135, you may notice one or more of these symptoms:

Check engine light illuminated
Slightly worse fuel economy during cold starts and short trips
Engine stays in open-loop (rich) mode longer than normal after starting
Higher cold-start emissions, possible failed emissions test
Possible rough or slightly unstable idle during the warm-up phase
No noticeable power loss once the engine is fully warm

What causes P0135?

Here are the most common causes of P0135:

Failed O2 sensor heater element - the internal heater inside the upstream sensor has burned out, so the sensor cannot reach operating temperature quickly (normal wear with age and mileage)
: high
Corroded or damaged wiring/connector at the sensor - heat-cycled or water-intruded pins break the heater circuit continuity
: medium
Blown O2 sensor heater fuse - heaters share a fuse, so a blown fuse cuts power and trips multiple heater codes at once
: medium
Faulty heater relay or supply circuit - the relay feeding the heater fails to close, leaving the sensor unheated
: low
Oil or coolant contamination - leaked fluid bakes onto the heater element and raises its resistance until it fails
: low
Faulty ECU heater driver circuit - the control module's internal heater driver stops switching the circuit (rare)
: low

Is it safe to drive with P0135?

Generally yes, for short-term driving. Safe to drive but more impactful than P0141. The upstream O2 sensor directly controls the fuel mixture, so the engine runs in open-loop (rich) mode until exhaust heat warms the sensor. Fuel economy and emissions are noticeably worse during cold starts.

How do you diagnose P0135?

Follow these steps to pinpoint the root cause of P0135:

Read all stored codes and note whether other heater codes (P0141, P0155, P0161) are present. Multiple heater codes together usually point to a shared fuse, relay, or wiring fault rather than one sensor
Locate and check the O2 sensor heater fuse in the fuse box. Replace it if blown and recheck before condemning the sensor
Unplug the Bank 1 Sensor 1 connector and measure heater resistance across the two heater pins. A healthy heater reads roughly 2-15 ohms. An open circuit (infinite reading) means the element has burned out, under 1 ohm suggests a short
Inspect the connector and pins for corrosion, melting, bent terminals, or water intrusion, and clean or repair as needed
Back-probe the connector with the key on and check for battery voltage on the heater supply wire. No voltage points to a fuse, relay, or wiring fault upstream of the sensor
Inspect the sensor wiring along its full run for chafing or melting against the exhaust manifold and heat shields, then clear the code and confirm it does not return

How much does P0135 cost to fix?

Repair costs for P0135 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–€3	€0–€0	€1–€3	Easy
Replace upstream O2 sensor (Bank 1)	€50–€180	€50–€120	€100–€300	Moderate
Repair wiring or connector	€5–€20	€40–€120	€45–€140	Moderate
Replace O2 sensor (OEM quality)	€80–€280	€50–€120	€130–€400	Moderate

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

Full repair guides

Oxygen Sensor Replacement Cost

P0135 on specific vehicles

P0135 behaves differently depending on your vehicle. Select your car below for model-specific causes and known issues:

P0135 on BMW

BMW 3 Series

See BMW-specific causes & cost

P0135 on Volkswagen

Volkswagen Golf

See Volkswagen-specific causes & cost

P0135 on Audi

Audi A4

See Audi-specific causes & cost

P0135 on Ford

Ford Focus

See Ford-specific causes & cost

P0135 on Toyota

Toyota Camry

See Toyota-specific causes & cost

P0135 on Honda

Honda Civic

See Honda-specific causes & cost

These codes are often seen alongside P0135 or indicate related issues:

Common questions about P0135

What does code P0135 mean?: P0135 means the heater circuit in the Bank 1, Sensor 1 oxygen sensor (the upstream, pre-catalyst sensor) is not working correctly. The internal heater that brings the sensor up to operating temperature has failed or lost power, so the sensor warms slowly and the engine takes longer to enter closed-loop fuel control.
What are the symptoms of P0135?: The main symptom is a check engine light. You may also notice slightly worse fuel economy on short trips and cold starts, a longer-than-normal warm-up before the engine runs smoothly, and higher cold-start emissions that can fail an emissions test. Once the engine is fully warm, power usually feels normal.
What causes a P0135 code?: The most common cause is a failed heater element inside the upstream oxygen sensor from normal wear with age and mileage. Other causes include a blown shared heater fuse (which usually trips several heater codes at once), corroded or damaged wiring and connectors, a faulty heater relay, or oil and coolant contamination baking onto the sensor.
Is it safe to drive with a P0135 code?: Yes, it is generally safe to drive in the short term. The engine still runs and the fault mostly affects cold-start fuel economy and emissions, not safety. A lit check engine light can get the car rejected at an emissions test, so fix it promptly. Driving on a check engine light also masks any new fault that appears later.
How do you fix and clear a P0135 code?: First check the heater fuse, then measure the sensor's heater resistance (about 2-15 ohms is healthy) and inspect the connector and wiring. If the heater reads open or out of range, replace the Bank 1, Sensor 1 oxygen sensor. After the repair, clear the code with a scan tool and drive through a warm-up cycle to confirm it does not return.
How much does it cost to fix P0135, and which sensor is it?: P0135 refers to Bank 1, Sensor 1, the upstream sensor before the catalytic converter on the cylinder bank that contains cylinder 1. A replacement upstream oxygen sensor typically costs 100 to 300 EUR including labour, with OEM-quality sensors up to about 400 EUR. If the fault is only a blown fuse, the fix can cost just a few euros.
Is P0135 worse than P0141?: Slightly. P0135 is the upstream (pre-catalyst) sensor, which directly controls fuel delivery, so until the heater warms it the ECU runs open-loop on a richer mixture. P0141 is the downstream monitor sensor and costs you nothing but the warning light. Both are safe to drive with, but P0135 hurts cold-start fuel economy on short trips.
Can P0135 cause P0171 or P0172?: Indirectly. While the heater should be working but is not, the ECU stays in open loop and may run richer than needed, which can set a fuel-trim code. If P0171 or P0172 appears alongside P0135, fix the heater fault first and see whether the trim code clears once closed-loop control is restored.

Read our detailed guides

Scan your car with Skanyx to diagnose P0135

Your car logged P0135. Skanyx reads it on a standard OBD2 adapter (Bluetooth LE on iPhone), tells you whether it is safe to keep driving, and shows the €1-€400 repair range so you know the number before a shop quotes you. Free on iPhone and Android, and you do not need to be a mechanic to read it.