P0063
HO2S Heater Control Circuit Low (Bank 2 Sensor 3)P0063 is a generic OBD-II powertrain diagnostic trouble code: HO2S Heater Control Circuit Low (Bank 2 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 P0063 means
Code P0063 is a generic SAE powertrain trouble code set when the Powertrain Control Module detects a low voltage condition in the heater control circuit of the third heated oxygen sensor on Bank 2 — the engine bank that does not contain cylinder number 1. The PCM drives the heater element to ground through an internal transistor and simultaneously monitors the circuit voltage; a reading persistently below the calibrated threshold indicates that the circuit is either shorted to ground, drawing excessive current, or that the ground driver itself is malfunctioning. The oxygen sensor heater element must reach approximately 750 °F (400 °C) for the electrochemical cell to generate meaningful voltage output; without adequate heater circuit function the sensor cannot monitor downstream catalytic converter efficiency as intended. Because Sensor 3 is positioned after the catalytic converter, its failure has minimal direct impact on immediate fuel trim calculations, but prolonged cold-start enrichment and inaccurate catalyst monitoring can elevate emissions and, over time, trigger catalyst efficiency codes. The most common repair involves replacing the oxygen sensor or repairing a wiring harness shorted to chassis ground, with the heater fuse frequently blown as a secondary consequence.
Common causes
Most-frequently reported root causes when P0063 is logged.
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1
Failed heater element inside the Bank 2 Sensor 3 oxygen sensor with an internal short to ground
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2
Heater control circuit wiring shorted to chassis ground
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3
Water or moisture ingress into the sensor connector blowing the heater-circuit fuse and causing a persistent low-voltage state
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4
Damaged or corroded wiring harness causing excessive resistance that mimics a low-voltage condition
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5
Faulty PCM heater control driver transistor outputting incorrect ground signal
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6
Corroded or broken exhaust system ground strap altering the circuit reference voltage
Symptoms drivers notice
How to diagnose P0063
A typical diagnostic flow when this code is present.
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1
Connect a scan tool, retrieve all stored and pending codes, and record freeze frame data; resolve any companion codes that could affect exhaust oxygen content before diagnosing P0063
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2
Visually inspect the Bank 2 Sensor 3 connector and wiring harness for signs of water intrusion, chafing, melted insulation near exhaust surfaces, or loose pins
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3
Inspect and test the heater-circuit fuse; water intrusion commonly blows this fuse as a first failure mode — if blown, seal the connector before fitting a new fuse
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4
With the key on and engine off, unplug the sensor and verify 12 V battery positive is present at the power supply wire of the harness connector; also verify the heater control (ground) circuit shows continuity and is not shorted to another ground
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5
Use an ohmmeter across the two heater terminals of the disconnected sensor to measure element resistance; an infinite reading indicates an open element and the sensor must be replaced; a reading near zero (dead short) also requires sensor replacement
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6
If wiring and sensor both test acceptable, perform a PCM heater driver output test per OEM factory procedures before considering PCM replacement
Related powertrain codes
Frequently asked questions
What does "circuit low" mean for P0063 compared to P0062?
"Circuit low" in P0063 means the PCM is detecting a voltage on the heater control line that is lower than expected — pointing to a short to ground or excessive current draw. P0062 is a broader open/incomplete circuit fault where no current flows at all. The distinction helps narrow the diagnosis: P0063 directs you to look for shorts to ground, while P0062 directs you to open circuits and missing power.
How serious is P0063?
It is generally a low-urgency repair from a drivability standpoint, since Sensor 3 downstream of the catalyst does not directly control the fuel mixture. However, the MIL will cause an emissions test failure, and ignoring it long-term risks accumulating companion catalyst monitor codes and increased cold-start emissions.
Could a bad ground strap cause P0063?
Yes. A corroded or broken exhaust system ground strap can alter the reference voltage seen by the PCM on the heater control circuit, causing the module to interpret the signal as abnormally low. Inspecting ground straps on the exhaust and engine block is a worthwhile step before replacing the sensor.
How much does it cost to fix P0063?
Repair cost typically ranges from $200 to $500 total. The oxygen sensor part itself costs roughly $100–$300 depending on vehicle and brand, with labour adding $100–$200. Wiring or connector repairs are often cheaper if the sensor itself is undamaged. Using OEM-specification sensors reduces the risk of recurrence compared to low-cost aftermarket alternatives.
Disabling P0063 in software
RaceTune can permanently disable P0063 — 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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