P0163 code: O2 Sensor Circuit Low Voltage (Bank 2, Sensor 3)
P0163 means o2 Sensor Circuit Low Voltage (Bank 2, Sensor 3). The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0163 means
This code reports that the third oxygen sensor on bank 2 — a position that exists only on vehicles with a second catalytic converter on that side — is stuck reporting low voltage, the electrical signature of an endlessly lean exhaust. Sitting after two converters, this sensor sees the most thoroughly cleaned exhaust in the system and has no role in fueling the engine, so the code is about monitoring integrity rather than performance. A pinned-low signal usually means the sensor has failed, the signal wire is shorted to ground somewhere along its long underbody run, or an exhaust leak just upstream is letting fresh air wash over the tip. Because outside air reads as lean, even a small leak at a flange or gasket near the sensor can hold the signal down.
P0163 symptoms
- Check-engine light and nothing else in most cases
- Failed emissions inspection
- No drivability changes to speak of
What it costs to fix P0163
Typical range: $100–$450 · about ~0.3–1.5 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| O2 sensor (Bank 2, Sensor 3) | $30–$200 | ~0.3–1 hrs |
| Wiring or connector repair | $5–$60 | ~0.5–1.5 hrs |
| Exhaust leak repair (gasket or flange) | $15–$100 | ~0.5–1.5 hrs |
Rear-of-vehicle sensors are usually easy to access, keeping labor short. Rust is the main cost driver — both for freeing a seized sensor and because rusted exhaust joints near the sensor are a common source of the leaks that trigger this code.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0163 for my exact vehicle →
How to fix P0163
Easy — basic tools, most owners can do this
- Confirm the sensor position and read the freeze frame
P0163 is the third oxygen sensor on bank 2 — the side without cylinder 1 — mounted after the second converter on that side, usually the furthest-back sensor under the car. Note the freeze-frame engine temperature, load, and speed, and check whether the bank 1 sensor 3 low-voltage code (P0143) set too: both at once points to a lean engine, not one bad sensor.
- Rule out a lean engine and bank 2 misfires
Scan for P0174, P0171, and misfire codes, and compare long-term fuel trims between banks. Misfiring bank 2 cylinders or a genuinely lean bank push extra oxygen through both converters, and the last sensor in line simply reports it; in that case the engine is the repair, not the sensor.
- Watch it rise during a sustained rich event
Behind two converters, sensor 3 moves slowly, so a quick throttle blip may not budge it. Hold a steady enrichment instead — propane at the intake or a sustained hard acceleration. A healthy sensor eventually climbs into the upper part of its range and falls again during a long closed-throttle coast; one pinned near zero through both is dead or shorted.
- Split sensor from wiring with the connector undone
Key off and sensor unplugged, measure resistance from the harness-side signal terminal to chassis ground. A dead short near zero ohms means the wire is grounded somewhere along its run; if fitted, run the same test on the bank 1 sensor 3 harness as a reference, since the computer's own input circuitry can show some resistance on a healthy wire.
- Inspect the underbody run and the joints just ahead of it
Look where the lead crosses brackets, heat shields, and the crossmember for insulation worn through to bare copper, and open the connector for water or salt corrosion. Then check the flange or clamp between the two bank 2 converters and the sensor's own port — soot tracks or a rust hole there let fresh air wash over the tip and hold it low.
- Replace the sensor and secure its wiring
With no lean condition, no short, and no leak found, fit a new sensor 3 with anti-seize on the threads and route the lead exactly as the original, using every clip. Clear the code and drive several warm cycles; the catalyst monitor needs to complete before an inspection station will see the system as ready.
DIY or shop? Most owners with ramps or jack stands can handle P0163 at home: the sensor is reached from underneath, and the decisive checks — lean and misfire codes, a sustained-enrichment test, and a resistance reading to ground — need only a scan tool and a multimeter. Leave it to a shop when the lean condition is real and needs a smoke test to locate, when the leak is a rusted joint between converters that has to be cut and welded, or when the sensor is corroded into its port so badly that removing it risks the threads.
Tools for the DIY steps: Scan tool with live data and freeze frame · Digital multimeter · Propane enrichment kit · O2 sensor socket · Jack stands or ramps · Penetrating oil
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0163.
Start a case with P0163 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P0163?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0163: common questions
Can an exhaust leak really cause P0163?
It can. Exhaust pulses can draw outside air in through a leak, and oxygen-rich outside air reads as lean — which drives the sensor voltage low. A leak at a flange or gasket just upstream of the sensor is a known cause worth checking before replacing anything.
Do I even need this third sensor?
Your vehicle was certified with it, so yes — the computer expects it, and the check-engine light will stay on without it. It exists to verify the second catalytic converter on that bank is working, which only matters for emissions, but that includes passing inspection.
How do I know which sensor is Bank 2, Sensor 3?
Bank 2 is the cylinder bank without cylinder 1, and Sensor 3 is the last sensor in that bank's exhaust path, after the second catalytic converter — typically the sensor furthest toward the rear of the vehicle on that side. A model-specific diagram removes the guesswork.
Is the fix for P0163 expensive?
Usually modest. Downstream sensors tend to be the cheaper ones, access at the rear of the exhaust is generally good, and a wiring or exhaust-gasket fix can cost even less than a sensor. The exception is a badly rusted exhaust that fights the repair.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0163 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P0163 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.