P0135: O2 Sensor Heater Circuit (Bank 1 Sensor 1)
P0135 means the engine computer has found a problem in the heater circuit for the upstream oxygen sensor on Bank 1. The most common fix is replacing the O2 sensor, or repairing its wiring or fuse if the sensor heater is not getting power, with typical repair costs of about $150 to $400.
- Severity
- Moderate
- Can I drive?
- Drive with caution
- DIY?
- Possible with some experience
- Repair cost range
- $90 – $1,400
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What does P0135 mean?
The Bank 1 Sensor 1 oxygen sensor sits in the exhaust stream before the catalytic converter and helps the engine computer adjust fuel mixture quickly. That sensor has an internal heater so it can warm up fast after startup and give accurate readings sooner. If the heater circuit fails, the sensor may work too slowly when the engine is cold, which can hurt fuel economy and emissions. The code usually points to an electrical problem, not a fuel mixture problem by itself.
Common symptoms
- Check engine light on
- Rough idle when cold
- Bad gas mileage
- Hesitation during warm-up
- Failed emissions test
Causes, fixes and costs
P0135: O2 Sensor Heater Circuit (Bank 1 Sensor 1)
General guide for most cars. Your car may differ.
The car will usually still run, but fuel control may be less accurate during cold starts and short trips. If the check engine light flashes, the engine runs badly, or the car starts stalling, stop driving and have it checked right away.
Most likely causes
- 1
Failed Bank 1 Sensor 1 oxygen sensor heaterHigh
A dead internal heater is the most common cause when the code comes back right away, especially on higher-mileage cars or if the sensor has slow warm-up symptoms.
Quick check: Inspect live data and resistance if available; if the heater circuit is open or out of range, replace the sensor.
- 2
Blown fuse or power supply problemMedium
If the code sets after a recent sensor replacement, or multiple heated sensors stop working at once, the heater may not be getting battery power.
Quick check: Check the O2 heater fuse and verify power at the sensor connector with the key on.
- 3
Damaged wiring or connectorMedium
Heat and road debris can melt, fray, or corrode the harness near the exhaust, causing an intermittent code or one that appears after bumps or rain.
Quick check: Look for burned insulation, loose pins, corrosion, or a connector pulled partially apart near the front exhaust.
- 4
Engine computer driver faultLow
If the sensor, fuse, and wiring all test good but the heater still has no command, the control side inside the PCM may be failing.
Quick check: A shop can verify heater command and circuit control with a scan tool and wiring tests.
Can you fix it yourself?
Possible with some experience
Difficulty: Moderate. A DIY check usually needs a scan tool, multimeter, and basic hand tools. Replacing the sensor is often straightforward, but diagnosing the heater power and wiring near the exhaust can be more difficult.
Show the stepsHide the steps
- Check for other O2 sensor or power-related codes
- Inspect the Bank 1 Sensor 1 wiring and connector for damage
- Check the heater fuse and related power feed
- Measure heater resistance at the sensor if specs are available
- Verify power and ground at the connector
- Replace the sensor if the heater is open or out of range
- Clear codes and confirm the code does not return
Estimated repair cost
$150 – $400
Replace Bank 1 Sensor 1 oxygen sensor: parts about $50-$180, labor about $100-$220
- Repair O2 sensor wiring or connector$120 – $300
- Replace blown fuse and diagnose power supply$90 – $180
- Replace engine computer driver after diagnosis$600 – $1,400
Actual prices vary by vehicle, engine layout, rust, and local labor rates.
Frequently asked questions
Can I drive with P0135?
Usually yes for short-term driving, but fix it soon. Fuel economy and cold-start performance can suffer, and you should stop driving if the engine runs rough, stalls, or the check engine light starts flashing.
Will P0135 clear itself?
Sometimes the light may go off after several good trips if the fault was temporary, but the problem usually comes back if the heater circuit is still bad. If it returns, the sensor, fuse, or wiring needs diagnosis.
Can I replace the O2 sensor myself?
Often yes, if the sensor is accessible and you can safely work under the car. Be careful with hot exhaust parts and seized sensors, and make sure you replace the correct Bank 1 Sensor 1 unit.
Will P0135 fail emissions inspection?
In many states it will, because the check engine light is on and the readiness monitors may not complete properly. The heater issue should be fixed before an inspection.
Is P0135 the same as a bad catalytic converter code?
No. P0135 points to the heater circuit for the upstream O2 sensor, while catalytic converter codes usually involve P0420 or P0430.
Related codes
Related problems
This guide covers most cars and is general advice, not an inspection. Prices are typical US independent-shop ranges and vary by region, car and shop. If your brakes, steering or a warning light feel unsafe, stop driving and contact a mechanic.