O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)
The P0155 code means the vehicle's onboard diagnostic system has detected: O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1). This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- moderate
- Estimated cost
- $100 - $350 (O2 sensor $80-$250; labor $50-$150)
Test O2 sensor voltage (should fluctuate 0.1-0.9V). Do not replace a $150 sensor without confirming it is actually bad first.
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
- Poor fuel economy during cold starts
- Engine runs rich during warm-up on bank 2
- Possible rough idle when cold
- Increased cold-start emissions
Probable Causes (Ranked by Likelihood)
- Failed O2 sensor heater element Very High
- Blown O2 sensor heater fuse High
- Open or shorted wiring in the heater circuit Moderate
- Corroded connector at the sensor Moderate
- PCM heater driver failure Low
Common Fixes by Vehicle
What techs usually find when diagnosing P0155 on specific vehicles — tap your vehicle for the fix and the exact part:
2009-2020 Ford F-150/Expedition 5.0L/3.5L Easy DIY
Bank 2 (passenger side) upstream O2 sensor heater circuit has failed. Check the O2 sensor heater fuse first. If the fuse is good, test heater resistance at the sensor connector (should be 4-8 ohms). Replace with an OE-quality Motorcraft unit. On EcoBoost models, inspect the wiring harness near the turbo for heat damage that can melt the insulation. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.
Labor: 30-45 min2010-2020 Chevrolet Silverado/Tahoe 5.3L Easy DIY
Bank 2 Sensor 1 heater circuit malfunction. The passenger side upstream O2 sensor is prone to corrosion from road salt. Test heater resistance at the connector -- should be 4-8 ohms. If open, replace with an OE-quality ACDelco unit. Also check the sensor wiring where it routes near the exhaust manifold for heat damage. Use penetrating oil before removal. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.
Labor: 30-45 min2007-2017 Toyota Highlander/Sienna 3.5L V6 Moderate DIY
Bank 2 upstream air-fuel ratio sensor heater has failed. The Bank 2 sensor is on the rear exhaust manifold near the firewall -- harder to access than Bank 1. Replace with an OE-quality Denso unit. Toyota uses a wideband A/F sensor with integrated heater. Check the fuse and wiring before condemning the sensor. Use a swivel socket for tight access. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.
Labor: 45 min - 1 hourFrequently Asked Questions
Can I drive with code P0155?
You can drive short distances. The O2 sensor on bank 2 will eventually warm up from exhaust heat alone, but this takes several minutes. During that time, the engine runs in open loop on bank 2, wasting fuel.
Is P0155 the bank 2 version of P0135?
Yes. P0135 is the heater circuit malfunction for bank 1 sensor 1, and P0155 is the same fault on bank 2 sensor 1. The diagnosis is identical.
Can a blown fuse cause P0155?
Yes. The heater fuse is one of the most common and easiest fixes. Check the underhood fuse box first. If the fuse is blown, replace it and check if it blows again, which would indicate a short in the circuit.
What actually makes the computer set an oxygen sensor code?
The OBD II regulation requires four separate detections for an oxygen sensor (Title 13 CCR 1968.2, section (e)(7.2)): deterioration in voltage, response rate or amplitude that would push emissions past 1.5 times the FTP standards; loss of circuit continuity; out-of-range values; and the case where the sensor has degraded enough that the fuel system stops using it and falls back to open loop. A sensor can therefore set a code while still producing a signal that looks plausible on a scan tool. This is the threshold the monitor is designed around, not a description of your specific fault — the regulation says what the system must detect, not how to find it on your vehicle.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
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Check the O2 sensor heater fuse and replace if blown.
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Disconnect the bank 2 sensor 1 O2 sensor and measure heater resistance (2-15 ohms typical). Open or shorted readings indicate a failed heater.
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Verify battery voltage at the heater power wire with the key on, engine off.
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Check the ground circuit from the sensor connector to the PCM for continuity.
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Inspect the wiring harness for heat damage, chafing, or breaks near the exhaust manifold.
Sources 3
This page is built from documented references. Verify against your own service info before repair work.
- California Code of Regulations, Title 13 section 1968.2 (OBD II)malfunction criteria, section (e)
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
Commonly Affected Vehicles
- 2007-2016 Toyota Tundra (5.7L V8)
- 2005-2014 Nissan Pathfinder (4.0L V6)
- 2008-2017 Honda Pilot (3.5L V6)
- 2009-2016 Ford F-150 (5.0L V8)
- 2010-2018 Chevrolet Silverado (5.3L V8)
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