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DTC codes / P00xx · Fuel and air metering and auxiliary emission controls / P0063

P0063HO2S Heater Control Circuit Low (Bank 2 Sensor 3)

P0063 means the powertrain control module (PCM) has detected an abnormally low voltage on the heater control circuit for the downstream oxygen sensor on bank 2, which is the side of the engine that does not contain cylinder number one. The PCM commands the heater on to bring the sensor up to operating temperature quickly, and it monitors the circuit for a voltage that stays below the expected threshold, indicating a short to ground, an open circuit, or excessive resistance.

SystemPowertrain
Code typeGeneric (all makes)
SeverityLow
Fix difficultyIntermediate
AreaFuel and air metering and auxiliary emission controls

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms.
  • A slight decrease in fuel economy because the sensor takes longer to reach closed-loop operation.
  • Increased emissions during cold starts or extended idle periods.
  • In some vehicles, a rough idle or hesitation when the engine is cold.
  • A pending code that may clear itself after several drive cycles if the fault is intermittent.

Common causes, most likely first

  1. A damaged or corroded heater element inside the bank 2 sensor 3 oxygen sensor.
  2. A short to ground in the heater control wire between the sensor and the PCM.
  3. An open circuit in the heater power feed or ground circuit, often due to a broken wire or poor connection.
  4. A faulty PCM driver for the heater circuit, though this is less common.
  5. Water intrusion or corrosion in the sensor connector causing high resistance.
  6. Aftermarket sensor with an incorrect heater resistance that does not match the vehicle's specification.

How to diagnose and fix it

  1. Inspect the bank 2 sensor 3 connector and wiring for corrosion, chafing, or loose pins, and repair as needed.
  2. Measure the resistance of the sensor heater element with a multimeter and compare it to the manufacturer's specification; replace the sensor if out of range.
  3. Check for continuity and short to ground on the heater control circuit between the sensor and the PCM; repair any wiring fault.
  4. Verify that the heater power feed and ground are intact and have low resistance; clean or repair grounds as necessary.
  5. Clear the code and perform a test drive to confirm the repair, monitoring the heater circuit voltage with a scan tool.
  6. If the wiring and sensor are good, test the PCM output for the heater control circuit; replace the PCM only if it fails the test.

What the heater circuit voltage really tells you

  • A low voltage on the heater control circuit often indicates a short to ground, but it can also be caused by an open heater element that prevents the circuit from pulling up to the expected voltage.
  • The bank 2 sensor 3 is typically the downstream sensor on the bank that does not contain cylinder one, so misidentifying the bank can lead to replacing the wrong sensor.
  • Some vehicles use a pulse-width modulated signal to control the heater, and a low voltage code can set if the duty cycle is not achieved even when the wiring is intact.
  • A faulty oxygen sensor heater can cause the sensor to remain inactive, leading to a false lean or rich code elsewhere, so always diagnose the heater circuit first.
  • After replacing a sensor, ensure the new unit has the correct heater resistance for the application; universal sensors with incorrect resistance are a common cause of repeat codes.

Can I keep driving with P0063?

You can generally continue driving with this code, but avoid extended idling and cold-start short trips until it is repaired, as the sensor may not reach operating temperature and emissions will be higher. If the check engine light begins flashing or you notice drivability issues, have it diagnosed promptly.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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