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P0163 Code Explained: O2 Sensor Circuit Low Voltage (Bank 2 Sensor 3) Causes, Symptoms & Fixes

P0163 code illustration showing the Bank 2 Sensor 3 oxygen sensor with a low-voltage warning, secondary catalytic converter, Check Engine Light, Pro Street TV logo, and www.ProStreetOnline.com.

If your OBD-II scanner displays P0163, your vehicle’s Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected that the Bank 2 Sensor 3 oxygen (O2) sensor voltage has remained below the manufacturer’s expected operating range for a specified period.

The generic OBD-II definition for P0163 is:

O2 Sensor Circuit Low Voltage (Bank 2 Sensor 3)

Bank 2 Sensor 3 is the third oxygen sensor located on the engine bank that does not contain cylinder number one. It is typically positioned after the secondary catalytic converter on vehicles equipped with multiple catalytic converters and three oxygen sensors per bank.

Unlike upstream oxygen sensors that control fuel delivery, Bank 2 Sensor 3 primarily monitors secondary catalytic converter efficiency and overall emissions system performance.

The PCM uses Bank 2 Sensor 3 to monitor:

When the PCM detects that the Bank 2 Sensor 3 voltage remains consistently lower than the calibrated threshold, it stores P0163 and usually illuminates the Check Engine Light.

Common causes include:

Unlike P0162, which indicates a general circuit malfunction, P0163 specifically indicates that the oxygen sensor signal voltage is too low.

What Does the P0163 Code Mean?

A zirconia oxygen sensor generates its own voltage by comparing oxygen levels inside the exhaust system to outside air.

Normally, Bank 2 Sensor 3 produces a relatively stable downstream voltage.

When the PCM continuously detects abnormally low voltage, it interprets the condition as either:

The code does not automatically mean the engine is running lean.

Where Is Bank 2 Sensor 3 Located?

Bank 2 Sensor 3 is mounted after the secondary catalytic converter on the cylinder bank opposite cylinder number one.

On vehicles equipped with three oxygen sensors per bank:

Many vehicles do not have a third oxygen sensor, making P0163 relatively uncommon.

Bank 2 Sensor 1 vs. Sensor 2 vs. Sensor 3

Understanding oxygen sensor locations makes diagnosis much easier.

Bank 2 Sensor 1

Located before the catalytic converter.

Responsible for:

Bank 2 Sensor 2

Located after the primary catalytic converter.

Responsible for:

Bank 2 Sensor 3

Located after the secondary catalytic converter.

Responsible for:

Because Sensor 3 primarily verifies emissions performance, P0163 rarely produces noticeable drivability issues.

How the Bank 2 Sensor 3 Oxygen Sensor Works

The downstream oxygen sensor measures the amount of oxygen remaining after exhaust gases pass through the secondary catalytic converter.

The PCM compares information from:

to evaluate the efficiency of the complete catalytic converter system.

If Sensor 3 consistently reports a voltage lower than expected, the PCM stores P0163.

What Does “Low Voltage” Mean?

Low voltage means the oxygen sensor signal remains below the manufacturer’s acceptable operating range.

Possible causes include:

The low-voltage condition may result from an actual exhaust-related issue or an electrical problem within the sensor circuit.

How the PCM Detects P0163

The PCM continuously monitors:

If Bank 2 Sensor 3 remains below the programmed voltage threshold for a specified time, the PCM stores P0163.

Most manufacturers require multiple failed drive cycles before permanently illuminating the Check Engine Light.

Why Bank 2 Sensor 3 Is Important

Although Sensor 3 does not directly control fuel delivery, it is essential for emissions compliance.

It helps the PCM evaluate:

Without accurate Sensor 3 information, the PCM cannot properly verify secondary catalyst performance.

Can a Bad Oxygen Sensor Cause P0163?

Yes.

A deteriorated Bank 2 Sensor 3 oxygen sensor is one of the most common causes of P0163.

Typical failures include:

As oxygen sensors age, their voltage output may gradually decrease until the PCM detects a low-voltage condition.

Can Wiring Problems Cause P0163?

Absolutely.

Electrical problems frequently trigger P0163.

Common wiring issues include:

Because Sensor 3 is located near the exhaust system, wiring is frequently exposed to high temperatures.

P0163 Quick Facts

ItemInformation
DTCP0163
Generic DefinitionO2 Sensor Circuit Low Voltage (Bank 2 Sensor 3)
SystemFuel & Emissions
Sensor LocationBank 2 Sensor 3
SeverityLow to Moderate
Safe to Drive?Yes (Usually)
Common SymptomsCheck Engine Light, failed emissions inspection, incomplete readiness monitors
Common CausesFailed oxygen sensor, damaged wiring, exhaust leaks, connector corrosion
Typical Repair Cost$100–700+
Related CodesP0162, P0164, P0165, P0166, P0167

Common Vehicles That Experience P0163

P0163 is commonly found on certain:

Vehicles equipped with three oxygen sensors per cylinder bank are the most likely to store this diagnostic trouble code.

What Does P0163 Really Mean?

The wording of P0163 often causes drivers to assume the engine is running lean.

The code does not automatically mean:

Instead, it means the PCM has detected that the Bank 2 Sensor 3 oxygen sensor signal remains lower than expected, preventing accurate emissions monitoring.

The problem may involve:

Think of P0163 as the PCM saying:

“The third oxygen sensor on Bank 2 is producing a voltage signal that’s lower than expected. I need the sensor and its electrical circuit inspected before I can accurately monitor secondary catalytic converter performance.”

Common P0163 Scan Tool Patterns

Monitoring live scan-tool data is one of the fastest ways to diagnose P0163.

Unlike P0162, which indicates a general circuit malfunction, P0163 specifically indicates the Bank 2 Sensor 3 oxygen sensor voltage remains lower than the manufacturer’s expected operating range.

Professional scan tools allow technicians to monitor oxygen sensor voltage, signal stability, catalyst monitor operation, and electrical performance to determine whether the low-voltage condition is caused by a failed oxygen sensor, exhaust leak, damaged wiring, poor ground, or PCM issue.

Pattern 1: Sensor Voltage Remains Low

The most common scan-tool pattern is:

Possible causes include:

Pattern 2: Other Oxygen Sensors Operate Normally

Compare:

If:

The fault is usually isolated to the Bank 2 Sensor 3 circuit.

This comparison helps eliminate engine fuel-control problems.

Pattern 3: Secondary Catalyst Monitor Fails

Monitor:

Common observations include:

Without an accurate downstream voltage signal, the PCM cannot properly evaluate secondary catalyst efficiency.

Pattern 4: Voltage Drops During Harness Movement

While monitoring live data:

If voltage changes suddenly, suspect:

Harness movement testing often identifies hidden electrical faults.

Pattern 5: Low Voltage Only After Warm-Up

Some vehicles only store P0163:

This often indicates:

Pattern 6: Low Voltage With Normal Heater Operation

Some scan tools indicate:

Possible causes include:

A properly functioning heater does not guarantee a healthy sensing element.

Common Symptoms of P0163

Because Bank 2 Sensor 3 primarily monitors emissions, drivability symptoms are generally minimal.

Common symptoms include:

Most drivers notice only the illuminated Check Engine Light.

Check Engine Light

The Check Engine Light is usually the first symptom.

Most manufacturers require:

before storing P0163.

Failed Emissions Inspection

P0163 commonly causes emissions failures because:

Even if the vehicle drives normally, it will often fail an emissions inspection.

Increased Exhaust Emissions

Without an accurate Bank 2 Sensor 3 signal:

Slight Fuel Economy Changes

Although uncommon, some vehicles may experience:

Since Sensor 3 does not directly control fuel delivery, these changes are usually very small.

Is P0163 Serious?

P0163 is generally considered a low-to-moderate severity diagnostic trouble code.

Most vehicles remain safe to drive.

However, delaying repairs may eventually result in:

Repairs should be completed before emissions testing.

Can You Drive With P0163?

Yes.

Driving is generally safe if:

Repairs should be scheduled promptly if:

P0163 vs Related Trouble Codes

Understanding related Bank 2 Sensor 3 codes simplifies diagnosis.

P0162

O2 Sensor Circuit Malfunction (Bank 2 Sensor 3)

General electrical fault affecting the oxygen sensor circuit.

P0163

O2 Sensor Circuit Low Voltage (Bank 2 Sensor 3)

The oxygen sensor voltage remains below manufacturer specifications.

P0164

O2 Sensor Circuit High Voltage (Bank 2 Sensor 3)

The oxygen sensor voltage remains above manufacturer specifications.

P0165

O2 Sensor Circuit Slow Response (Bank 2 Sensor 3)

The oxygen sensor reacts slower than expected.

P0166

O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 3)

The PCM detects no usable oxygen sensor signal.

P0167

O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 3)

Electrical fault affecting the oxygen sensor heater circuit.

30 Common Causes of P0163

The most common causes include:

  1. Failed Bank 2 Sensor 3 oxygen sensor
  2. Open signal wire
  3. High circuit resistance
  4. Exhaust leak
  5. Broken wiring harness
  6. Connector corrosion
  7. Loose electrical connector
  8. Melted wiring near the exhaust
  9. Poor ground connection
  10. Internal sensor deterioration
  11. Carbon contamination
  12. Oil contamination
  13. Coolant contamination
  14. Moisture intrusion
  15. Heat damage
  16. Rodent damage
  17. Previous wiring repairs
  18. Incorrect replacement sensor
  19. Damaged PCM connector
  20. Charging system voltage problems
  21. Secondary catalytic converter damage
  22. Exhaust modifications
  23. Wiring short to ground
  24. Weak heater element
  25. Electrical interference
  26. Internal connector damage
  27. PCM software issue
  28. Internal PCM driver fault
  29. Harness routing damage
  30. PCM failure (rare)

Final Thoughts

The P0163 O2 Sensor Circuit Low Voltage (Bank 2 Sensor 3) code indicates the PCM has detected that the third oxygen sensor on Bank 2 is consistently producing a voltage signal lower than expected. While a deteriorated oxygen sensor is one of the most common causes, exhaust leaks, damaged wiring, connector corrosion, poor grounds, high circuit resistance, and electrical faults can all produce the same low-voltage condition.

Proper diagnosis should determine whether the fault originates in:

The next section of this guide covers:

Following a structured diagnostic process prevents unnecessary oxygen sensor replacement while restoring accurate secondary catalyst monitoring and proper OBD-II readiness.

Related Pro Street Diagnostic Guides

How to Diagnose the P0163 Code

Diagnosing P0163 requires determining why the Bank 2 Sensor 3 oxygen sensor is producing a voltage signal that remains lower than the manufacturer’s expected operating range.

Unlike P0162, which indicates a general circuit malfunction, P0163 specifically indicates that the oxygen sensor voltage is consistently too low.

The low-voltage condition may be caused by:

Proper diagnosis should determine whether the problem originates in the oxygen sensor, the electrical circuit, the exhaust system, or the PCM before replacing expensive components.

Safety Precautions

Before beginning diagnosis:

Bank 2 Sensor 3 is typically mounted near the secondary catalytic converter where temperatures frequently exceed 800°F (425°C).

Tools Required

Professional diagnosis may require:

An oscilloscope provides the most accurate method for analyzing oxygen sensor voltage patterns.

Step 1 – Verify the Code

Connect a professional scan tool.

Record:

Monitor:

Always save freeze-frame information before clearing diagnostic trouble codes.

Step 2 – Check for Related Trouble Codes

P0163 commonly appears with:

Related codes often simplify diagnosis.

Code CombinationLikely Diagnosis
P0163 onlyLow-voltage sensor fault
P0163 + P0162Electrical circuit problem
P0163 + P0166Sensor signal failure
P0163 + P0420Secondary catalyst concern
Multiple oxygen sensor codesWiring or PCM issue

Repair related faults before replacing major components.

Step 3 – Monitor Live Oxygen Sensor Data

Allow the engine to reach operating temperature.

Observe:

Normal operation:

Abnormal operation:

These conditions indicate additional testing is required.

Step 4 – Compare Other Oxygen Sensors

Compare:

If:

The fault is usually isolated to Bank 2 Sensor 3 or its circuit.

Comparing all oxygen sensors helps eliminate engine fuel-control issues.

Step 5 – Inspect the Oxygen Sensor

Inspect Bank 2 Sensor 3 for:

Physical contamination can affect voltage output.

Step 6 – Inspect the Electrical Connector

Disconnect the oxygen sensor connector.

Inspect for:

Poor electrical connections commonly produce low-voltage conditions.

Step 7 – Inspect the Wiring Harness

Inspect wiring between the oxygen sensor and PCM.

Look for:

Heat-damaged wiring is one of the leading causes of P0163.

Step 8 – Test Signal Circuit Continuity

Using a digital multimeter:

Measure continuity between:

Inspect for:

Repair wiring faults before replacing the oxygen sensor.

Step 9 – Verify Ground Integrity

Inspect the oxygen sensor ground circuit.

Measure:

Inspect for:

Poor grounds commonly create low-voltage sensor signals.

Step 10 – Inspect for Exhaust Leaks

Inspect the exhaust system before Bank 2 Sensor 3.

Look for:

Exhaust leaks may introduce outside oxygen, causing the sensor to report a falsely low voltage.

Step 11 – Test for High Circuit Resistance

Using a multimeter:

Measure:

High resistance can reduce sensor voltage and trigger P0163.

Step 12 – Evaluate Secondary Catalyst Performance

Monitor:

If Sensor 2 operates normally while Sensor 3 consistently reports low voltage, the problem is usually isolated to Sensor 3 or its electrical circuit.

Step 13 – Review Technical Service Bulletins

Before replacing expensive components:

Review manufacturer Technical Service Bulletins (TSBs).

Look for updates involving:

Software updates occasionally resolve false low-voltage codes.

Step 14 – Review Freeze-Frame Data

Compare current operating conditions with stored freeze-frame information.

Review:

Freeze-frame data often identifies the operating conditions that triggered P0163.

Step 15 – Inspect PCM Connector Integrity

Inspect PCM connectors for:

Poor PCM connections may interrupt oxygen sensor communication.

Step 16 – Test the Oxygen Sensor Using an Oscilloscope

An oscilloscope provides the most accurate diagnosis.

Evaluate:

A consistently low waveform confirms the low-voltage condition.

Step 17 – Verify Charging System Voltage

Measure charging voltage.

Normal charging voltage should remain between:

Low charging voltage can contribute to unstable oxygen sensor operation.

Step 18 – Confirm Sensor Power Supply

Verify:

Improper electrical supply may contribute to abnormal sensor voltage.

Step 19 – Inspect Previous Repairs

Inspect for:

Improper repairs frequently create intermittent low-voltage conditions.

Step 20 – Confirm the Diagnosis

Before replacing any major component, verify:

Completing these diagnostic steps prevents unnecessary oxygen sensor replacement while accurately identifying the root cause of P0163.

Step 21 – Replace the Bank 2 Sensor 3 Oxygen Sensor

If testing confirms the Bank 2 Sensor 3 oxygen sensor has failed internally and consistently produces a low-voltage signal, replacement is the proper repair.

General replacement procedure:

  1. Allow the exhaust system to cool completely.
  2. Disconnect the oxygen sensor electrical connector.
  3. Remove the sensor using an oxygen sensor socket.
  4. Inspect the sensor threads and catalytic converter bung.
  5. Install an OEM or high-quality replacement oxygen sensor.
  6. Tighten the sensor to the manufacturer’s specified torque.
  7. Reconnect the electrical connector.
  8. Clear all diagnostic trouble codes.
  9. Verify proper sensor operation with a professional scan tool.

OEM oxygen sensors typically provide more accurate voltage output, faster response, and longer service life than inexpensive aftermarket sensors.

Step 22 – Repair Damaged Wiring

Inspect the complete Bank 2 Sensor 3 wiring harness.

Repair:

Wiring faults are one of the most common causes of P0163.

Step 23 – Repair Connector Problems

Inspect the complete oxygen sensor connector.

Repair or replace:

Poor electrical connections frequently reduce oxygen sensor voltage.

Step 24 – Repair Ground Circuit Problems

Inspect:

Measure:

Poor grounds commonly create low-voltage oxygen sensor signals.

Step 25 – Repair Exhaust Leaks

Inspect the exhaust system upstream of Bank 2 Sensor 3.

Repair:

Exhaust leaks allow outside oxygen into the exhaust stream, causing the oxygen sensor to report falsely low voltage.

Step 26 – Repair High-Resistance Circuits

Measure resistance throughout the sensor circuit.

Inspect:

Repair excessive resistance before replacing expensive components.

Step 27 – Repair Charging System Problems

Low charging voltage can affect oxygen sensor operation.

Inspect:

Normal charging voltage should remain between:

Correct charging system problems before replacing emissions components.

Step 28 – Update PCM Software

Before replacing the PCM:

Review manufacturer Technical Service Bulletins (TSBs).

Manufacturers occasionally release PCM software updates addressing:

Always verify the PCM contains the latest available calibration.

Step 29 – Verify Oxygen Sensor Operation

After repairs:

Monitor:

A healthy downstream oxygen sensor should produce a stable voltage signal that allows the PCM to accurately evaluate secondary catalytic converter performance.

Step 30 – Consider PCM Failure

PCM failure is extremely uncommon.

Only suspect the PCM after confirming:

PCM replacement should always be the final diagnostic step.

How to Fix P0163

The proper repair depends entirely on the diagnostic results.

Common repairs include:

Verifying the Repair

After completing repairs:

  1. Clear all diagnostic trouble codes.
  2. Start the engine.
  3. Allow the engine to reach operating temperature.
  4. Monitor Bank 2 Sensor 3 voltage.
  5. Verify stable downstream oxygen sensor activity.
  6. Complete a full drive cycle.
  7. Confirm oxygen sensor and catalyst readiness monitors complete.
  8. Verify no pending or permanent DTCs return.
  9. Perform a final scan to confirm a successful repair.

A successful repair restores accurate secondary catalyst monitoring, completes emissions readiness monitors, and eliminates the low-voltage condition.

Typical Repair Costs

RepairTypical Cost
Professional diagnosis$100–250
Bank 2 Sensor 3 replacement$175–500
Wiring repair$100–400
Open circuit repair$100–350
High-resistance circuit repair$100–400
Exhaust leak repair$150–700
Connector replacement$100–300
Ground circuit repair$100–250
Battery replacement$150–350
Alternator replacement$400–1,000
PCM software update$100–250
PCM replacement$800–2,000+

Repair costs vary depending on vehicle design, labor rates, oxygen sensor accessibility, and the root cause of the low-voltage condition.

Common Diagnostic Mistakes

Avoid these common mistakes:

Many P0163 repairs involve correcting wiring or exhaust leaks rather than replacing the oxygen sensor.

Manufacturer-Specific Notes

Ford

Inspect:

Heat-damaged wiring is a common cause of P0163 on Ford vehicles.

General Motors (Chevrolet/GMC)

Verify:

Poor grounds and damaged wiring commonly trigger P0163 on GM applications.

Toyota/Lexus

Inspect:

Toyota factory scan tools provide enhanced downstream oxygen sensor diagnostics.

Honda/Acura

Inspect:

Connector corrosion commonly contributes to intermittent low-voltage conditions.

Nissan/Infiniti

Verify:

High exhaust temperatures frequently damage Sensor 3 wiring over time.

BMW/Mercedes-Benz

Inspect:

Factory diagnostic software provides advanced oxygen sensor circuit analysis.

Hyundai/Kia

Inspect:

Electrical connector corrosion is a common source of P0163.

Frequently Asked Questions

What usually fixes P0163?

The most common repairs include replacing the Bank 2 Sensor 3 oxygen sensor, repairing damaged wiring, fixing exhaust leaks, replacing faulty connectors, repairing poor grounds, correcting high-resistance circuits, or updating PCM software.

Can I drive with P0163?

Yes. Most vehicles remain drivable, but repairs should be completed before emissions testing because P0163 commonly prevents secondary catalyst readiness monitors from completing.

Does P0163 always mean the oxygen sensor is bad?

No. Exhaust leaks, damaged wiring, connector corrosion, poor grounds, high-resistance circuits, and PCM communication problems can all trigger P0163 without the oxygen sensor itself being defective.

Can an exhaust leak cause P0163?

Yes. An exhaust leak ahead of Bank 2 Sensor 3 can introduce fresh oxygen into the exhaust stream, causing the sensor to report an abnormally low voltage and triggering P0163.

Can P0163 cause a failed emissions inspection?

Yes. Because Bank 2 Sensor 3 monitors secondary catalyst efficiency, P0163 commonly prevents OBD-II readiness monitors from completing and usually causes an emissions inspection failure.

Is P0163 a serious code?

P0163 is generally considered a low-to-moderate severity diagnostic trouble code. While it rarely affects drivability, it can increase emissions, interrupt secondary catalyst monitoring, and prevent emissions compliance if left unrepaired.

Final Thoughts

The P0163 O2 Sensor Circuit Low Voltage (Bank 2 Sensor 3) code indicates the PCM has detected that the third oxygen sensor on Bank 2 is consistently producing a voltage signal lower than expected. While a deteriorated oxygen sensor is one of the most common causes, exhaust leaks, damaged wiring, connector corrosion, poor grounds, high-resistance circuits, and electrical faults can all produce the same low-voltage condition.

A complete diagnosis should always verify:

Following a structured diagnostic process prevents unnecessary parts replacement while restoring accurate secondary catalyst monitoring, emissions compliance, and complete OBD-II readiness.

Continue Your Pro Street Bank 2 Sensor 3 Series

Related guides include:

These guides provide comprehensive coverage of downstream oxygen sensor diagnostics, secondary catalyst monitoring, emissions system troubleshooting, and advanced OBD-II repair procedures.

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