Car & driving · Free
P0135: O2 sensor heater circuit (bank 1, sensor 1)
P0135 means the heater inside the front oxygen sensor on bank 1 does not work. This is the sensor the engine uses to control its mixture, so after every cold start the engine waits longer before it can fine-tune its fuel. In most cases the sensor has failed, but check the fuse and the plug first.
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- Runs on your device
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Check your car for P0135
Runs on your device
Connect your OBD2 adapter
- Plug the adapter into the OBD2 port – usually under the steering wheel, near the pedals.
- Switch the ignition on, or start the engine.
- Bluetooth adapter? Turn Bluetooth on. Nothing else to set up.
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Classic Bluetooth adapter (PIN 1234)? Pair it in your system settings first, then choose USB or paired Bluetooth – on a computer or in Chrome 138+ on Android. Wi-Fi adapters cannot work in a browser.
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What P0135 means
The front O2 sensor, before the catalytic converter, is the one the engine computer relies on to control the mixture. It gives a useful signal only once its tip is several hundred degrees hot, so it contains an electric heater that brings it up to temperature soon after a cold start.
The computer switches the heater on and watches the current it draws. If that current is missing, too low or too high, it stores P0135 for bank 1, sensor 1. Without the heater, the computer has to wait until the exhaust gas has warmed the sensor before it can switch to precise fuel control, so after every cold start the engine runs longer on its fixed, slightly rich settings.
Symptoms of P0135
- Usually no change you can feel once the engine is warm.
- Higher fuel consumption on short trips, because the engine stays longer in its warm-up mode.
- More emissions after a cold start and an O2 sensor heater self-test that stays incomplete.
Causes of P0135, cheapest first
Work down the list in order: the first checks cost little or nothing, the last ones are jobs for a workshop.
A blown fuse
Sensor heaters draw a fair amount of current and often share a fuse. If several heater codes appear at once, check that fuse first.
A cooked plug or harness near the manifold
The front sensor sits close to the hot exhaust manifold or turbo. Look for melted insulation, brittle wires and a plug that has been baked.
A failed heater element
The most common cause. Measure the heater resistance at the sensor plug with a multimeter: an open circuit means the heater is broken. Front sensors are often wideband types that cost more, so confirm before you buy.
A sensor poisoned by oil or coolant
An engine that burns oil or leaks coolant into the exhaust can coat the sensor and kill it, heater included. If a new sensor fails quickly, look for that cause.
The engine control unit
Rarely, the heater driver in the computer fails. Suspect it only after the sensor, fuse and wiring have tested good.
Can you drive with P0135?
Safe to drive. Once warm, the engine runs normally. Short trips cost a little more fuel and produce more emissions, and the O2 sensor self-tests cannot complete, so plan the repair before the next emissions inspection.
Check P0135 with OBD Studio
Connect your adapter above, or try the demo car, then:
- After a cold start, watch Fuel system status in Live data. It should switch from open loop (engine cold) to closed loop within a minute or two; with a dead front heater it takes noticeably longer, especially at idle.
- Graph O2 sensor 1 at the same time. A classic sensor starts switching between rich and lean once it is hot; a wideband sensor starts following the mixture with its lambda value.
- In Fault codes, check whether other heater codes are stored too: several at once point to the fuse or a shared wire.
- After the repair, clear the code. The O2 sensor heaters monitor in Inspection completes on the next cold start.
More fault code guides
Each of these codes has its own page with causes ranked by cost and the checks that go with them.
- P0420Catalyst efficiency below threshold
- P0171System too lean
- P0300Random or multiple misfire
- P0455EVAP system large leak
- P0442EVAP system small leak
- P0128Engine warms up too slowly
- P0172System too rich
- P0401EGR flow too low
- P0101Air flow sensor implausible
- P0016Crankshaft and camshaft out of step
- P0011Intake camshaft timing over-advanced
- P0141Rear O2 sensor heater
- P0113Intake air temperature sensor high
- P0457Fuel cap loose or missing
- P0299Turbo underboost
- P0700Transmission control system fault
- P0087Fuel rail pressure too low
- P0562System voltage low
- U0100Lost communication with engine computer
More OBD Studio pages
Frequently asked questions
Do I have to replace the O2 sensor for P0135?
Usually yes, because the heater is built into the sensor. Before you buy one, check the fuse and the plug, and measure the heater resistance to be sure.
Which sensor is bank 1 sensor 1?
It is the oxygen sensor before the catalytic converter on the side of the engine with cylinder 1. On a four-cylinder engine with one exhaust manifold, it is simply the front O2 sensor.
Why does fuel consumption rise with P0135?
Until the front sensor is hot, the engine computer runs the engine on fixed values that lean to the rich side. Without the heater that phase lasts longer after every start, which you notice most on short trips.
Can I read P0135 without going to a workshop?
Yes. With any ELM327-compatible Bluetooth LE or USB adapter, OBD Studio on this page reads P0135 and every other stored code for free, shows the freeze frame and clears the code after the repair. Nothing to install, no account.
