P0064
HO2S Heater Control Circuit High (Bank 2 Sensor 3)P0064 is a generic OBD-II powertrain diagnostic trouble code: HO2S Heater Control Circuit High (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 P0064 means
Code P0064 is stored when the powertrain control module (PCM) detects an abnormally high voltage or resistance in the heater control circuit of the heated oxygen sensor located at Bank 2, Sensor 3 — the third oxygen sensor downstream on the side of the engine that does not contain cylinder #1. Heated oxygen sensors (HO2S) incorporate an internal heating element that brings the sensor to its minimum operating temperature of approximately 750°F (400°C) quickly after startup, enabling accurate exhaust gas measurement before the exhaust stream itself is hot enough to do so. The PCM manages the heater duty cycle based on coolant temperature and engine load. When the PCM commands the heater circuit and monitors feedback voltage that is above the expected high threshold — indicating a short to voltage, excessive resistance, or an internal sensor fault — it sets P0064 and illuminates the MIL. On most vehicles the sensor in question is a post-catalytic-converter monitor positioned well downstream; its primary role is catalyst efficiency monitoring rather than fuel trim control, which is why drivability impacts are often subtle. Extended operation with a failed downstream heater can allow the sensor to run cold, causing inaccurate catalyst efficiency readings, failed emissions tests, and potentially masking catalyst degradation over time.
Common causes
Most-frequently reported root causes when P0064 is logged.
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1
Failed HO2S internal heater element (most common cause, typically from heat cycling fatigue or moisture intrusion)
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2
Short to voltage in the heater control wire between the PCM and the sensor connector
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3
Corroded or damaged sensor connector causing elevated contact resistance
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4
Open circuit in the heater ground return path
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5
Blown heater circuit fuse or failed heater relay in the control circuit
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6
PCM output driver failure for the Bank 2 Sensor 3 heater circuit
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7
Wiring chafed against exhaust components, creating an intermittent short to battery positive
Symptoms drivers notice
How to diagnose P0064
A typical diagnostic flow when this code is present.
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1
Record and clear the code; perform a drive cycle to confirm it is active and not historical
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2
Inspect the B2S3 sensor connector and wiring harness for corrosion, melted insulation, or chafing near the exhaust
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3
Measure heater circuit resistance at the sensor connector: a healthy HO2S heater typically measures 4–30 Ω depending on temperature; open or near-zero resistance indicates a failed element
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4
With the ignition on, verify the control voltage from the PCM side of the connector with a DVOM; a voltage higher than the commanded high side (usually battery voltage on the heater supply) while the PCM commands low suggests a short to voltage
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5
Check and replace any blown fuse associated with the downstream O2 sensor heater circuit
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6
If wiring and fuse are intact and sensor resistance is out of spec, replace the HO2S Bank 2 Sensor 3
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7
If a new sensor immediately re-sets the code, inspect for PCM driver failure or a persistent short in the harness before replacing the PCM
Related powertrain codes
Frequently asked questions
Can I drive with a P0064 code stored?
Yes, in most cases the vehicle remains driveable with no immediate mechanical risk. However, you should address it promptly because the downstream O2 sensor is needed for catalyst efficiency monitoring, and ignoring it can mask a failing catalytic converter until more expensive damage occurs.
Is Bank 2 Sensor 3 the same as the post-cat sensor?
Sensor 3 numbering means it is the third sensor in the exhaust stream on Bank 2, which on most V-configuration engines is behind the catalytic converter. On some vehicles with two cats per bank there may be a Sensor 3 after the second converter. Always verify sensor location with a vehicle-specific wiring diagram.
Why does my fuel economy drop with a heater circuit fault?
A cold downstream sensor provides inaccurate voltage signals that can confuse fuel trim logic in some calibrations and delay closed-loop operation on cold starts, leading to slightly richer mixtures until the sensor self-heats via exhaust flow alone, which takes considerably longer than with a functioning heater.
Could a faulty PCM cause P0064 without a bad sensor?
Yes, though it is uncommon. The PCM's output driver for the heater circuit can fail and send continuous high voltage or fail to pull the circuit low. Always verify the sensor and wiring first before suspecting the PCM, as PCM replacement is expensive and rarely the root cause.
Disabling P0064 in software
RaceTune can permanently disable P0064 — 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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