If your OBD-II scanner displays P0063, your vehicle’s Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected a low-voltage condition in the heated oxygen sensor heater control circuit for Bank 2 Sensor 3.
The generic SAE definition for P0063 is:
HO2S Heater Control Circuit Low Bank 2 Sensor 3
This code indicates that voltage in the heater control circuit has dropped below the expected range or that the circuit is drawing more current than the ECM considers normal.
Bank 2 Sensor 3 is generally the third oxygen sensor located on the side of the engine opposite cylinder number one. On vehicles equipped with this sensor configuration, it is typically positioned downstream of an additional or secondary catalytic converter.
Not every vehicle uses a Bank 2 Sensor 3. P0063 is mainly found on vehicles with:
- Multiple catalytic converters
- Three oxygen sensors on each exhaust bank
- Advanced catalyst-monitoring systems
- Dual exhaust systems
- Certain diesel and luxury-vehicle exhaust layouts
Common causes of P0063 include:
- Shorted oxygen sensor heater
- Heater control wire shorted to ground
- Melted wiring near the exhaust
- Water or corrosion inside the connector
- Incorrect oxygen sensor
- Failed oxygen sensor heater
- Damaged ECM control circuit
- ECM heater driver failure
P0063 usually does not cause major drivability problems because Sensor 3 primarily monitors emissions-system performance. However, the fault can prevent readiness monitors from completing and cause the vehicle to fail an emissions inspection.
For additional diagnostic information, visit:
- Complete OBD-II Code Library: https://my.prostreetonline.com/dtc-obdii/
- Body B-Code Library: https://my.prostreetonline.com/dtc-doctor/b-code-obd-ii-codes/
- Chassis C-Code Library: https://my.prostreetonline.com/dtc-doctor/c-code-obd-ii-codes/
P0063 Quick Facts
| Item | Information |
|---|---|
| OBD-II Code | P0063 |
| Description | HO2S Heater Control Circuit Low Bank 2 Sensor 3 |
| Category | Powertrain |
| System | Emissions |
| Sensor | Bank 2 Sensor 3 |
| Typical Location | After an Additional or Secondary Catalytic Converter |
| Severity | Low to Moderate |
| Safe to Drive? | Usually |
| Typical Repair Cost | $75–650 |
What Does P0063 Mean?
P0063 means the ECM has detected lower-than-expected voltage in the Bank 2 Sensor 3 heater control circuit.
A low circuit condition can occur when:
- The heater draws excessive current
- The control wire shorts to ground
- The heater element becomes internally shorted
- Damaged wiring lowers circuit resistance
- Moisture or corrosion creates an unintended electrical path
- The ECM control driver remains grounded
The internal heater helps the oxygen sensor reach operating temperature quickly. When the heater circuit voltage remains too low, the ECM stores P0063 and illuminates the Check Engine Light.
What Is Bank 2 Sensor 3?
Bank 2 is the side of the engine that does not contain cylinder number one.
Sensor 3 refers to the third oxygen sensor positioned along that exhaust bank.
Depending on the vehicle, Bank 2 Sensor 3 may be located:
- After a secondary catalytic converter
- Behind an underfloor catalytic converter
- Farther downstream than Bank 2 Sensor 2
- Near the rear portion of the exhaust system
Its functions may include:
- Monitoring secondary catalytic converter efficiency
- Measuring oxygen content after multiple catalysts
- Verifying emissions-system operation
- Supporting OBD-II catalyst readiness monitors
- Detecting deterioration in an additional converter
Sensor layouts vary by manufacturer, engine, and exhaust configuration. Always confirm the exact location with service information before replacing parts.
Does Every Vehicle Have Bank 2 Sensor 3?
No.
Most vehicles use one or two oxygen sensors on each exhaust bank.
Bank 2 Sensor 3 is generally limited to vehicles with complex exhaust and catalyst-monitoring systems.
A vehicle can only set P0063 if its ECM is programmed to monitor a third oxygen sensor on Bank 2.
Before buying a sensor, verify that the vehicle actually has one. Otherwise, the parts counter may happily sell you a solution to a sensor arrangement your exhaust system never received.
Why Does Sensor 3 Need a Heater?
Oxygen sensors must reach a high operating temperature before producing accurate readings.
The internal heater allows Bank 2 Sensor 3 to warm up quickly after startup.
This enables the ECM to:
- Begin catalyst monitoring sooner
- Complete readiness tests faster
- Reduce cold-start emissions
- Verify secondary catalyst operation
- Detect sensor and catalyst failures earlier
Without a working heater, the sensor may eventually become hot enough through exhaust heat, but it will take longer than the ECM expects.
How the Heater Control Circuit Works
A typical oxygen sensor heater circuit includes:
- Battery voltage
- Heater fuse
- Heater relay or power feed
- Oxygen sensor heater element
- ECM-controlled ground circuit
- Wiring harness
- Electrical connectors
On many vehicles, one side of the heater receives battery voltage.
The ECM controls the opposite side by switching the ground circuit on and off through an internal transistor.
The ECM may monitor:
- Circuit voltage
- Current draw
- Heater resistance
- Duty cycle
- Warm-up time
- Sensor response
If the control circuit voltage remains below the expected range, P0063 may be stored.
What Does “Circuit Low” Mean?
“Circuit low” generally means the ECM sees less voltage than expected on the heater control circuit.
This may be caused by:
- A short to ground
- Excessive current draw
- An internally shorted heater
- Melted wires touching the exhaust
- Crossed wiring
- A stuck ECM ground driver
Circuit low does not necessarily mean the battery voltage itself is low.
It usually refers to the voltage the ECM measures on the specific oxygen sensor heater control circuit.
How the ECM Detects P0063
The ECM typically checks the heater circuit during cold starts and under specific operating conditions.
It compares:
- Commanded heater operation
- Actual circuit voltage
- Current flow
- Heater resistance
- Sensor warm-up speed
P0063 may be triggered when:
- Control circuit voltage remains too low
- Heater current is excessive
- The control wire is shorted to ground
- The heater element is internally shorted
- The ECM commands the heater off but the circuit remains grounded
- The sensor does not warm as expected
Depending on the vehicle, the Check Engine Light may illuminate after one failed test or after the condition repeats across multiple drive cycles.
P0062 vs P0063 vs P0064
| Code | Description |
| P0062 | HO2S Heater Control Circuit Bank 2 Sensor 3 |
| P0063 | HO2S Heater Control Circuit Low Bank 2 Sensor 3 |
| P0064 | HO2S Heater Control Circuit High Bank 2 Sensor 3 |
Generally:
- P0062 indicates a general heater circuit malfunction.
- P0063 indicates a low-voltage or excessive-current condition.
- P0064 indicates a high-voltage or insufficient-current condition.
Manufacturer-specific diagnostic logic may vary.
Symptoms of P0063
Common symptoms include:
- Check Engine Light
- Failed emissions inspection
- Catalyst monitor not ready
- Oxygen sensor monitor incomplete
- Increased cold-start emissions
- Additional heater circuit codes
- Repeated blown heater fuse in some cases
Most drivers will not notice:
- Rough idle
- Reduced engine power
- Poor acceleration
- Major fuel economy changes
Because Sensor 3 generally monitors catalyst operation rather than controlling the air/fuel mixture, drivability symptoms are uncommon.
Common Causes of P0063
1. Heater Control Wire Shorted to Ground
A damaged control wire may contact:
- The exhaust system
- The vehicle body
- A heat shield
- Another grounded wire
- A metal bracket
This can pull circuit voltage low and trigger P0063.
2. Internally Shorted Oxygen Sensor Heater
The heater element inside Bank 2 Sensor 3 may develop an internal short.
This increases current draw and lowers circuit voltage.
3. Melted Wiring Near the Exhaust
Sensor 3 wiring often runs close to hot exhaust components.
If the harness becomes loose, the insulation may melt against:
- Catalytic converters
- Exhaust pipes
- Mufflers
- Heat shields
This is one of the most important areas to inspect.
4. Water or Corrosion in the Connector
Moisture and corrosion may create an unintended electrical path to ground.
Inspect for:
- Green corrosion
- Water intrusion
- Dirty terminals
- Damaged weather seals
- Bent or loose pins
5. Incorrect Oxygen Sensor
Universal or incorrect replacement sensors may have:
- Different heater resistance
- Incorrect wire assignments
- Excessive current draw
- Poor splice connections
Use a high-quality direct-fit sensor whenever possible.
6. Damaged Wiring From Previous Repairs
Poorly repaired or incorrectly spliced wiring may cause:
- Crossed heater wires
- Weak insulation
- Exposed conductors
- Short circuits
- Incorrect connector pinning
7. Failed Oxygen Sensor Heater
A heater does not always fail completely open.
It may deteriorate internally and begin drawing too much current before total failure.
8. Shorted Relay or Power Circuit
A damaged relay or power feed may cause abnormal circuit behavior.
This is less common than a sensor or wiring fault but should be considered if multiple heater codes are present.
9. ECM Control Driver Stuck Grounded
The ECM’s internal heater-control transistor may fail in the grounded position.
This is uncommon and should only be suspected after the sensor and wiring have been thoroughly tested.
10. Incorrect ECM Programming or Module Fault
Rarely, software or internal ECM problems may cause incorrect heater control.
Always verify technical service information before replacing an ECM.
Is P0063 Serious?
P0063 is generally considered a low- to moderate-severity diagnostic trouble code.
The vehicle will usually continue running normally.
However, the code deserves prompt attention because a shorted heater circuit can cause:
- Blown fuses
- Damaged wiring
- Overheated connectors
- ECM driver damage
- Incomplete readiness monitors
- Failed emissions testing
A visible short or melted wiring should be repaired immediately.
Can You Drive With P0063?
Yes, in many cases.
Because Bank 2 Sensor 3 normally monitors emissions rather than fuel delivery, the engine may continue operating without noticeable problems.
However, driving with an active short circuit may:
- Continue overheating wiring
- Blow a shared fuse
- Disable other oxygen sensor heaters
- Damage the ECM driver
- Cause additional trouble codes
The car may drive normally, but the wiring harness could be quietly preparing a more expensive sequel.
How to Diagnose P0063
Step 1: Scan for Additional Codes
Check for:
- P0061
- P0062
- P0064
- Other oxygen sensor heater codes
- Catalyst-efficiency codes
- System-voltage codes
- Fuse or relay-related faults
Record freeze-frame data before clearing codes.
Multiple heater codes may indicate a shared fuse, relay, or power-feed problem.
Step 2: Verify the Vehicle Uses Bank 2 Sensor 3
Confirm that the vehicle is equipped with:
- Bank 2
- Sensor 3
- A dedicated heater circuit for that sensor
Use manufacturer service information or a reliable exhaust diagram.
Step 3: Identify Bank 2
Locate cylinder number one.
The opposite cylinder bank is Bank 2.
Do not identify Bank 2 based only on driver-side or passenger-side position, because engine layouts vary.
Step 4: Locate Sensor 3
Trace the Bank 2 exhaust path downstream.
Sensor 3 is generally located after an additional catalytic converter and farther downstream than Sensor 2.
Step 5: Inspect the Harness
Look for:
- Melted insulation
- Bare copper
- Burned wires
- Chafing
- Pinched sections
- Loose routing clips
- Contact with the exhaust
- Damaged previous repairs
Pay special attention to hidden wiring above heat shields.
Step 6: Inspect the Connector
Disconnect the sensor and inspect both connector halves.
Look for:
- Corrosion
- Water intrusion
- Bent pins
- Loose terminals
- Burned plastic
- Missing seals
- Broken locking tabs
Repair connector problems before replacing the sensor.
Step 7: Check the Heater Fuse
Inspect the correct oxygen sensor heater fuse.
If it is blown:
- Do not immediately replace it.
- Disconnect Bank 2 Sensor 3.
- Inspect the wiring for a short.
- Test the heater resistance.
- Check whether other sensors share the circuit.
A replacement fuse that immediately blows is not defective. It is simply delivering the same bad news more efficiently.
Step 8: Measure Heater Resistance
Disconnect the sensor and measure resistance across the heater terminals.
Possible results include:
- Near-zero resistance: internally shorted heater
- Resistance below specification: excessive current draw likely
- Infinite resistance: open heater
- Resistance within specification: continue testing the circuit
Always compare the reading with manufacturer specifications.
Step 9: Test for a Short to Ground
With the sensor disconnected, test the heater control wire for continuity to ground.
There should not be unintended continuity unless the ECM is actively commanding the circuit.
If a short remains after disconnecting the ECM, the wiring is damaged.
Step 10: Check Heater Power
Verify battery voltage is available at the heater power terminal when commanded.
If power is missing, inspect:
- Fuse
- Relay
- Power feed
- Junction points
- Shared heater circuits
Although P0063 points toward a low control circuit, the entire circuit should still be verified.
Step 11: Test the ECM Control Wire
Check the control circuit between the sensor and ECM for:
- Continuity
- Short to ground
- Short to voltage
- Excessive resistance
- Crossed wiring
Voltage-drop testing under load may reveal faults that a continuity test misses.
Step 12: Command the Heater With a Scan Tool
If bidirectional controls are available, command the Bank 2 Sensor 3 heater on and off.
Monitor:
- Circuit voltage
- Heater current
- Control duty cycle
- Sensor warm-up response
If the circuit remains grounded when commanded off, suspect a wiring short or ECM driver fault.
Step 13: Replace the Sensor if Necessary
Replace Bank 2 Sensor 3 if testing confirms:
- Heater resistance below specification
- Excessive current draw
- Internal short
- Failure to respond correctly despite good wiring
Use an OEM or quality direct-fit sensor.
Step 14: Verify the Repair
After completing repairs:
- Clear all diagnostic trouble codes.
- Perform a cold start.
- Monitor heater circuit voltage.
- Confirm proper sensor warm-up.
- Complete the manufacturer’s drive cycle.
- Confirm readiness monitors complete.
- Verify P0063 does not return.
Common Repairs and Costs
| Repair | Estimated Cost |
| Oxygen sensor replacement | $175–600 |
| Wiring repair | $100–450 |
| Connector replacement | $75–275 |
| Heater fuse replacement | $10–50 |
| Relay replacement | $50–225 |
| Exhaust-damaged harness repair | $150–650 |
| ECM circuit diagnosis | $150–500 |
| ECM replacement | $1,000–2,500+ |
Repair costs depend on sensor accessibility, labor rates, exhaust configuration, and the extent of any wiring damage.
Common Diagnostic Mistakes
Avoid these common mistakes:
- Assuming every vehicle has a Sensor 3
- Replacing Bank 2 Sensor 2 by mistake
- Guessing which side is Bank 2
- Replacing the sensor without checking for a short to ground
- Installing another fuse without finding the short
- Missing melted wiring above a heat shield
- Using an incorrect universal oxygen sensor
- Replacing the ECM before testing the control wire
- Ignoring other heater codes that share the same fuse
The sensor is often guilty, but the exhaust-melted wiring deserves a fair trial before the parts cannon is loaded.
Vehicles Commonly Affected
P0063 is relatively uncommon because few vehicles use Bank 2 Sensor 3.
It may appear on certain:
- Audi vehicles
- BMW vehicles
- Mercedes-Benz models
- Volkswagen vehicles
- Toyota and Lexus models
- Nissan and Infiniti vehicles
- General Motors trucks and SUVs
- Diesel-powered vehicles
- Luxury vehicles with multiple catalytic converters
Exact sensor arrangements vary by model, engine, year, and exhaust configuration.
Always confirm the vehicle’s sensor layout before ordering replacement parts.
How to Prevent P0063
Reduce the likelihood of P0063 by:
- Securing oxygen sensor wiring away from the exhaust
- Reinstalling heat shields after service
- Using OEM-quality direct-fit sensors
- Avoiding poor-quality wiring splices
- Repairing damaged connector seals
- Inspecting the harness during exhaust repairs
- Correcting oil and coolant leaks
- Investigating repeated fuse failures
- Maintaining battery and charging-system health
Frequently Asked Questions
What does P0063 mean?
P0063 means the ECM has detected a low-voltage condition in the Bank 2 Sensor 3 oxygen sensor heater control circuit.
Where is Bank 2 Sensor 3 located?
It is generally located on the side of the engine opposite cylinder number one and downstream of an additional or secondary catalytic converter.
The exact location varies by vehicle.
Does every vehicle have Bank 2 Sensor 3?
No.
Only vehicles equipped with a third oxygen sensor on Bank 2 can set P0063.
Is P0063 serious?
Usually not from a drivability standpoint.
However, a shorted heater circuit can damage wiring, blow fuses, or damage the ECM driver.
Can I drive with P0063?
Usually, yes.
However, damaged or overheating wiring should be repaired promptly.
What commonly causes P0063?
Common causes include:
- Heater wire shorted to ground
- Internally shorted oxygen sensor
- Melted wiring
- Corroded connector
- Incorrect replacement sensor
- ECM driver failure
Will replacing the oxygen sensor fix P0063?
It may if the heater is internally shorted.
The wiring and control circuit should always be tested first.
What is the difference between P0062 and P0063?
P0062 indicates a general Bank 2 Sensor 3 heater circuit malfunction.
P0063 specifically indicates a low-voltage or excessive-current condition.
What is the difference between P0063 and P0064?
P0063 indicates the heater circuit voltage is too low.
P0064 indicates the circuit voltage is too high.
Can P0063 blow a fuse?
Yes.
An internally shorted heater or grounded wire can draw excessive current and blow the oxygen sensor heater fuse.
Can P0063 cause an emissions failure?
Yes.
The code can prevent oxygen sensor and catalyst readiness monitors from completing.
Final Thoughts
The P0063 code indicates that the ECM has detected low voltage in the Bank 2 Sensor 3 oxygen sensor heater control circuit. The most common causes include an internally shorted heater, damaged wiring grounded against the exhaust, corrosion inside the connector, or an incorrect replacement sensor.
Because this sensor usually monitors emissions rather than fuel delivery, the vehicle may continue driving normally. However, an electrical short can damage wiring, repeatedly blow fuses, or overload the ECM heater driver.
Confirm the vehicle actually uses Bank 2 Sensor 3, inspect the harness around hot exhaust components, test heater resistance, and check the control circuit for a short to ground before replacing parts. Proper diagnosis is considerably cheaper than repeatedly donating new fuses to the same unresolved electrical problem.
Related Articles
Bank 2 Sensor 3 Heater Codes
- P0061 Code Explained: HO2S Heater Resistance Bank 2 Sensor 3
- P0062 Code Explained: HO2S Heater Control Circuit Bank 2 Sensor 3
- P0064 Code Explained: HO2S Heater Control Circuit High Bank 2 Sensor 3
Other Bank 2 Heater Codes
- P0050 Code Explained: HO2S Heater Control Circuit Bank 2 Sensor 1
- P0051 Code Explained: HO2S Heater Control Circuit Low Bank 2 Sensor 1
- P0052 Code Explained: HO2S Heater Control Circuit High Bank 2 Sensor 1
- P0056 Code Explained: HO2S Heater Control Circuit Bank 2 Sensor 2
- P0057 Code Explained: HO2S Heater Control Circuit Low Bank 2 Sensor 2
- P0058 Code Explained: HO2S Heater Control Circuit High Bank 2 Sensor 2
Browse the complete Pro Street diagnostic libraries:
- Complete OBD-II Guide: https://my.prostreetonline.com/dtc-obdii/
- B-Code Guide: https://my.prostreetonline.com/dtc-doctor/b-code-obd-ii-codes/
- C-Code Guide: https://my.prostreetonline.com/dtc-doctor/c-code-obd-ii-codes/
