P0163 Code: O2 Sensor Circuit Low Voltage (Bank 2 Sensor 3)

What the P0163 code means

Most vehicles carry two oxygen sensors per bank: one before the catalytic converter and one after it. Some models, especially those that fit two converters in series to meet stricter regulations, add a third one at the end of the line.

The P0163 code belongs to that third sensor on bank 2, which is the side of the engine that does not hold cylinder number one. Its job is to evaluate the second catalytic converter.

The code means the voltage of its signal fell below the expected minimum. A healthy sensor in that position keeps a steady signal at mid-range values, not low, so a signal stuck low points to an open circuit, a short to ground or a worn-out sensor.

The location shapes the diagnosis. Being the sensor farthest from the engine, its wiring is the longest and the most exposed: it runs through a good part of the underside of the vehicle, where rubbing, road salt and water punish it. The wire fails more often than the sensor.

Keep in mind that sensors are always numbered in the direction of exhaust flow, from the engine toward the tailpipe. Sensor 1 is the closest to the engine, sensor 2 is the next one and sensor 3 is the last. Mixing up that order is easy and leads to removing the wrong sensor, especially on vehicles where all three look physically identical and sit a meter and a half (about 5 feet) of pipe apart.

It is worth knowing why some vehicles carry three sensors per bank. The strictest emissions regulations call for two catalytic converters in series, one close to the engine that heats up fast and another under the floor that works at steady conditions. Each one needs to be evaluated separately, and that is where the third sensor comes in.

That means this code does not appear on most vehicles, and if your scan tool shows it you should confirm that the model really has that sensor before you go looking for it. Some generic tools list codes that the vehicle cannot generate.

P0163 code symptoms

• Check engine light on.
• Engine runs with no noticeable change.
• The catalytic converter monitor does not reach ready status.
• Failed emissions inspection.
• Catalytic converter codes may be stored alongside it.
• Slightly higher fuel use on some vehicles.
• The code shows up on a vehicle that does not have three sensors per bank, which points to a scan tool error.

Likely causes of the P0163 code

1. Wiring damaged under the vehicle by rubbing, stones or road salt. The main suspect because of how long the route is.
2. Connector with water or corrosion.
3. Sensor worn out by mileage.
4. Signal wire shorted to ground.
5. Sensor contaminated by burning oil or coolant.
6. Exhaust leak near the sensor, which throws off its reading.
7. Circuit ground with high resistance.
8. Universal sensor with poorly made splices.

How to diagnose the P0163 code step by step

1. Identify the sensor physically before anything else: the third one on bank 2 is the one farthest from the engine on that side.
2. Raise the vehicle and follow the wire along its whole route. This is the check that solves the most cases because of the length of the run.
3. Watch the signal in live data. It should stay steady at mid-range values, not stuck low.
4. Check the connector for water, green corrosion and backed-out pins.
5. Rule out a short to ground on the signal wire with the computer connector unplugged.
6. Check the circuit ground and its voltage drop.
7. Compare with the equivalent sensor on bank 1 if the vehicle has one.
8. Look for exhaust leaks near the sensor.
9. Confirm that your model really has three sensors per bank before you go looking for it. Some generic scan tools list codes that the vehicle cannot generate.

How to fix the P0163 code

• Repair damaged wiring with solder and heat-resistant sleeving, securing it along the original route.
• Clean or replace the corroded connector and protect it with dielectric grease.
• Replace the sensor if its signal stays stuck low with the circuit in good shape.
• Repair exhaust leaks near the sensor.
• Restore the circuit ground down to bare metal.
• Avoid universal sensors that need splicing on a circuit this long.
• Deal with the oil burning if it contaminated the sensor.
• Check the reading with another scan tool if the vehicle does not have that sensor, because it may be a tool error.

Apply penetrating oil ahead of time before removing the sensor: because of its exposure to water and salt, the thread is often seized.

Technical reference data

• Expected signal of a downstream sensor with a healthy converter: steady between 0.6 and 0.8 volts.
• Threshold that sets the code: signal below 0.2 volts for a sustained period.
• Bank 2 is the side of the engine that does not hold cylinder number one.
• Sensor 3 only exists on vehicles with two catalytic converters in series per bank.
• Usual torque: 40 to 50 N·m (about 30 to 37 lb-ft).
• The third sensor only exists on vehicles with two catalytic converters in series per bank, called for by stricter regulations.

Brand-specific notes

Being the sensor farthest from the engine, its wiring covers the longest distance in the whole system. That makes it the most exposed to rubbing, chewing and moisture, and it explains why the wire fails more often than the sensor itself. Before you order the part, follow the entire wire with a flashlight.

If the vehicle has equivalent sensors on both banks, compare their readings. The healthy one gives you a direct reference and saves you from digging through specifications.

Frequently asked questions about P0163