The last oxygen sensor on bank 2 should see very little oxygen once the exhaust has passed through two catalytic converters. If its voltage stays low, the engine computer thinks oxygen is getting in somewhere. A P0163 code means the bank 2 sensor 3 voltage stayed too low for too long.
This guide explains why a sensor this far back reads low, how to test it and how to fix the problem.
P0163 Code Breakdown
Every OBD-II code follows the same five-character pattern set by the SAE J2012 standard. Each character narrows down which system has the fault. This table shows what each part of the code tells you.
| Character | Meaning | What It Tells You |
|---|---|---|
| P | Powertrain | The fault is in the engine or transmission systems. |
| 0 | Generic (SAE) code | The definition is the same on every OBD-II vehicle. |
| 1 | Fuel and air metering | The fault involves the sensors that measure air and fuel. |
| 63 | Specific fault | O2 Sensor Circuit Low Voltage (Bank 2 Sensor 3) |
What the P0163 Code Means
The SAE J2012 standard defines the P0163 code as O2 Sensor Circuit Low Voltage (Bank 2 Sensor 3). Sensor 3 sits after the second catalytic converter on the side of the engine opposite cylinder 1.
With warm converters, sensor 3 usually holds a steady reading around 0.5 to 0.8 volt. When the powertrain control module (PCM) sees it stay below about 0.2 volt during conditions when it should read higher, it sets the code.
The most common reason is outside air leaking into the exhaust near the sensor. A short to ground in the signal wire is the next most likely cause.
Symptoms of a Low Bank 2 Sensor 3 Reading
Drivability rarely changes, since sensor 3 does not control fuel. Watch for these signs of a P0163 code:
- Check engine light on
- Catalyst monitor that will not complete
- Failed emissions test
- Exhaust noise or smell from a leak near the back of the vehicle
What Causes the P0163 Code?
A low reading this far back points to air leaks or wiring faults first. These are the common causes:
- Exhaust leak near the sensor. Rusted pipes, holes and loose clamps let air in.
- Signal wire shorted to ground. Damaged insulation touching metal pulls the voltage low.
- Failed oxygen sensor. A worn sensor may stick low.
- Heater fault. A sensor that stays cool makes little voltage.
- Lean bank 2. A severe lean condition on that side lowers every downstream reading.
- Corroded connector. Resistance weakens the signal.
How to Diagnose the P0163 Code
You need a scan tool with live data and a multimeter. Drive at least 15 minutes so all converters are hot.
Check Bank 2 Fuel Trims
Look at long-term fuel trims for both banks. High positive numbers on bank 2 mean that side runs lean, which could affect every bank 2 sensor. If trims are normal, focus on the sensor, its wiring and exhaust leaks near it.
Compare Both Sensor 3 Readings
Graph bank 1 sensor 3 and bank 2 sensor 3 together. Add a little propane near the intake at idle. Both should rise toward 0.8 volt within several seconds, though slower than the front sensors. If bank 1 rises and bank 2 stays low, the bank 2 sensor or its wiring is at fault, or an exhaust leak sits near it.
Inspect the Exhaust and Wiring
With the exhaust cold, check the pipes around bank 2 sensor 3 for holes, soot marks and loose joints. Follow the wiring to its connector and look for spots where it rubs the body or touches hot parts.
How to Fix the P0163 Code
Repair the cause, clear the code and drive until the monitors complete.
- Repair exhaust leaks near the sensor, such as a rusted pipe or loose flange.
- Fix a shorted signal wire.
- Correct bank 2 lean running if fuel trims are high.
- Replace bank 2 sensor 3 if it fails the propane test.
- Repair the heater circuit if heater codes appear too.
When you replace the sensor, compare the new part with the old one before you install it. The connector, wire length and number of wires should match. Add a small amount of anti-seize to the threads if the new sensor does not have it, and keep it off the tip.
Repair Cost Breakdown
Most P0163 code repairs involve the exhaust pipe or the sensor. This table shows typical costs.
| Repair | DIY Cost | Typical Shop Cost |
|---|---|---|
| Bank 2 sensor 3 replacement | $30 to $130 | $120 to $350 |
| Exhaust pipe section | $30 to $150 | $150 to $500 |
| Wiring repair | $10 to $30 | $100 to $300 |
| Vacuum leak repair | $10 to $80 | $100 to $400 |
Is It Safe to Drive with a P0163 Code?
Usually, yes. The engine runs on the front sensors, so it drives normally. You will fail an emissions test until the fault is fixed.
An exhaust leak under the vehicle can let fumes into the cabin. If you smell exhaust inside, open the windows and get the leak repaired quickly.
Related Codes
These codes often show up with this one or point to the same system:
| Code | Meaning |
|---|---|
| P0160 | O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 2) |
| P0161 | O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 2) |
| P0162 | O2 Sensor Circuit Malfunction (Bank 2 Sensor 3) |
| P0164 | O2 Sensor Circuit High Voltage (Bank 2 Sensor 3) |
| P0165 | O2 Sensor Circuit Slow Response (Bank 2 Sensor 3) |
Fixing a Low Bank 2 Sensor 3 Reading
A P0163 code means the bank 2 sensor 3 voltage stays too low. Exhaust leaks, shorted wiring and worn sensors cause most cases.
- Check bank 2 fuel trims for a lean condition.
- Compare both sensor 3 readings during a propane test.
- Look for exhaust leaks around the sensor.
- Replace the sensor only if it fails to rise.
Frequently Asked Questions
Why Is Sensor 3 Slower Than the Front Sensors?
Two catalytic converters sit ahead of sensor 3. They store and release oxygen, which smooths out changes in the exhaust. So the signal at sensor 3 changes slowly by design. A slow reaction is normal, but a reading that never rises is not.
Can a Rusty Exhaust Cause the P0163 Code?
Yes. Rust holes near the sensor are a top cause on older vehicles. Exhaust pulses pull outside air through the holes, and the sensor reads that oxygen as lean. A pipe repair can clear the code without a new sensor.
Will a New Converter Fix This Code?
Not usually. A low sensor 3 reading points to air leaks, wiring or the sensor itself. Converter problems tend to set efficiency codes instead. Test the sensor and exhaust before spending money on a converter.
Can a Bad Front Sensor Cause This Code?
Indirectly. A faulty bank 2 front sensor can make that side run lean, and the lean exhaust reaches sensor 3 too. If you also see front sensor codes or high fuel trims on bank 2, fix those first and then recheck sensor 3.