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.
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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
- 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
Step-by-Step Diagnostic Procedure
-
Check the O2 sensor heater fuse and replace if blown.
-
Disconnect the bank 2 sensor 1 O2 sensor and measure heater resistance (2-15 ohms typical). Open or shorted readings indicate a failed heater.
-
Verify battery voltage at the heater power wire with the key on, engine off.
-
Check the ground circuit from the sensor connector to the PCM for continuity.
-
Inspect the wiring harness for heat damage, chafing, or breaks near the exhaust manifold.
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 Motorcraft DY-1401. On EcoBoost models, inspect the wiring harness near the turbo for heat damage that can melt the insulation.
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 ACDelco 213-4573. Also check the sensor wiring where it routes near the exhaust manifold for heat damage. Use penetrating oil before removal.
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 Denso 234-9052. 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.
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.
Sources
This page is built from documented references. Verify against your own service info before repair work.
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