O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
The P0135 code means the vehicle's onboard diagnostic system has detected: O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1). This is a moderate severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- medium
- Estimated cost
- $50-$250 for O2 sensor; $10-$20 for fuse
Test O2 sensor voltage (should fluctuate 0.1-0.9V). Do not replace a $150 sensor without confirming it is actually bad first.
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Shows real-time O2 sensor readings on your phone. See if the sensor is lazy, stuck, or actually working before spending money.
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Common Symptoms
- Check Engine Light on
- Extended open-loop operation after cold start (rich running while warm-up)
- Poor cold-start fuel economy
Probable Causes (Ranked by Likelihood)
- Failed O2 sensor heater element Very High
- Blown fuse for O2 sensor heater circuit Moderate
- Open or shorted wiring to heater circuit Moderate
Step-by-Step Diagnostic Procedure
-
Check the O2 sensor heater fuse in the fuse box.
-
Test heater element resistance at the sensor connector: typical spec is 3-15 ohms. Open circuit means the heater is burned out.
-
With the key on engine running, verify 12V supply to the heater circuit at the connector.
-
Replace the O2 sensor if the heater element has failed.
Common Fixes by Vehicle
What techs usually find when diagnosing P0135 on specific vehicles — tap your vehicle for the fix and the exact part:
2007-2017 Toyota Camry/Corolla 2.5L easy DIY
The upstream O2 sensor heater circuit has failed. Replace the Bank 1 Sensor 1 air-fuel ratio sensor (Denso 234-9052). Toyota uses a wideband sensor with an integrated heater. Before replacing, check the 15A EFI fuse and the wiring connector for corrosion. The sensor is located on the exhaust manifold -- use penetrating oil before removal.
Labor: 30 min2008-2019 Honda Accord/CR-V 2.4L easy DIY
The upstream A/F sensor heater element burns out around 100-120K miles. Replace with Denso 234-9066 or NTK 24302. Check the sensor relay and 20A fuse in the underhood fuse box before condemning the sensor. Honda uses a 5-wire wideband sensor -- do not substitute a standard 4-wire O2 sensor. Apply anti-seize to the threads during installation.
Labor: 30 min2009-2020 Ford F-150/Explorer 3.5L/5.0L easy DIY
Check the O2 sensor heater fuse first (15A in the battery junction box). If the fuse is good, test heater circuit resistance at the sensor connector -- should be 4-8 ohms. If open, replace the sensor (Motorcraft DY-1401). On EcoBoost models, the sensor wiring near the turbo is prone to heat damage. Inspect harness routing carefully.
Labor: 30-45 min2010-2020 Hyundai Sonata/Kia Optima 2.4L easy DIY
The upstream O2 sensor heater fails prematurely on Theta II engines due to excessive exhaust heat from oil burning issues. Replace with Denso 234-9037. Also check for engine oil consumption -- if burning more than 1 quart per 1000 miles, the engine may qualify for Hyundai/Kia engine replacement warranty extension. TSB 18-01-0087 covers sensor diagnosis.
Labor: 30 minFrequently Asked Questions
Why does the O2 sensor have a heater?
The heater brings the sensor to operating temperature (approximately 600 degrees F) quickly after a cold start so the engine can enter closed-loop fuel control within 30-60 seconds instead of waiting for exhaust heat alone, which could take several minutes.
Sources
This page is built from documented references. Verify against your own service info before repair work.
P0135 on Diesel, EV & Equipment
The same code ID appears across other engines and platforms. The diagnostic flow varies by manufacturer — these are the platform-specific breakdowns:
See All Codes & Fixes for Your Vehicle
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