P0055
HO2S Heater Resistance (Bank 1, Sensor 3)P0055 is a generic OBD-II powertrain diagnostic trouble code: HO2S Heater Resistance (Bank 1, Sensor 3). It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0055 means
DTC P0055 is triggered when the ECM detects that the heater element resistance of the Bank 1, Sensor 3 heated oxygen sensor falls outside the allowable programmed range. Sensor 3 on Bank 1 is a third oxygen sensor positioned further downstream in the exhaust system — found on vehicles with two catalytic converters in series or with an additional underfloor catalyst. It is used for monitoring the efficiency of the second catalytic stage and, in some calibrations, for secondary fuel trim adjustments. Like all heated oxygen sensors, Sensor 3 contains an internal resistive heating element that the ECM energises during cold starts to accelerate sensor warm-up. A failed heater element (open circuit) or high-resistance wiring fault causes the ECM to detect out-of-range current draw and set P0055. Because Sensor 3 is further from the engine, it is more exposed to road debris and more prone to connector corrosion from moisture. While P0055 has limited immediate driveability impact, it prevents full catalyst monitoring, increases tailpipe emissions during cold operation, and will cause failure at emissions inspections.
Common causes
Most-frequently reported root causes when P0055 is logged.
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1
Failed internal heater element in the Bank 1, Sensor 3 HO2S (most common)
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2
Blown oxygen sensor heater fuse
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3
Damaged or chafed wiring due to the sensor's remote underbody location and road exposure
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4
Corroded or moisture-contaminated connector (underbody location increases exposure risk)
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5
Open circuit in heater supply or ground wire
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6
Cracked or leaking second catalytic converter housing allowing oxygen infiltration
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7
Faulty ECM heater-driver output (rare)
Symptoms drivers notice
How to diagnose P0055
A typical diagnostic flow when this code is present.
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1
Identify the exact Sensor 3 location on your specific vehicle using a service diagram — on dual-cat exhaust configurations it can be in an unexpected underfloor position
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2
Check the oxygen sensor heater fuse; underbody wiring damage can blow fuses intermittently
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3
Inspect the wiring harness and connector for road damage, moisture ingress, or corrosion — underbody sensors are more vulnerable than manifold-mounted sensors
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4
Disconnect the sensor and measure heater pin resistance with a DVOM; compare against the OEM specification for this sensor position
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5
Verify heater supply voltage and ground continuity at the connector with the circuit energised
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6
After repair, clear codes and run a complete drive cycle to confirm the catalyst monitor completes successfully
Related powertrain codes
Frequently asked questions
Which vehicles have a Bank 1 Sensor 3?
Vehicles with two catalytic converters on the same exhaust bank — typically larger displacement V6 and V8 engines, some premium European models, and certain diesel applications with SCR systems — may have a third oxygen or NOx sensor on Bank 1.
Is P0055 a serious fault?
It is a moderate emissions fault. Driveability is typically unaffected, but the vehicle will fail an OBD emissions inspection due to an incomplete catalyst monitor, and cold-start emissions increase.
Can I reset P0055 and just drive?
Clearing the code will temporarily extinguish the MIL, but it will return once the heater circuit is re-evaluated on the next cold start. The underlying fault must be repaired for the code to stay clear.
How does P0055 relate to P0053 and P0054?
All three share the same root cause — heater element failure or heater circuit wiring fault — but at different sensor positions on Bank 1. P0053 is pre-catalyst (Sensor 1), P0054 is post-first-catalyst (Sensor 2), and P0055 is post-second-catalyst (Sensor 3). Diagnostic procedure is identical; only sensor location and resistance spec differ.
Disabling P0055 in software
RaceTune can permanently disable P0055 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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