P0164 code: O2 Sensor Circuit High Voltage (Bank 2, Sensor 3)
P0164 means o2 Sensor Circuit High 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 P0164 means
P0164 flags the opposite condition from P0163: the post-second-catalyst sensor on bank 2 is reporting persistently high voltage, which on this type of sensor means a rich exhaust. After the gas has passed through two catalytic converters, the sensor should read fairly steady and moderate — a signal pinned high for long periods is not believable, so the computer flags the circuit. The realistic causes are a failing or contaminated sensor, or the signal wire shorted to a voltage source, commonly its own heater feed after insulation wears through. A genuinely rich-running engine can contribute, but that almost always announces itself first through upstream codes like P0175. Only vehicles with a second converter on bank 2 have this sensor, and it plays no part in how the engine is fueled.
P0164 symptoms
- Check-engine light with normal driving
- Failed emissions test
- Rich-running symptoms (fuel smell, poor mileage) only if a mixture problem is the root cause
What it costs to fix P0164
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 |
A straightforward sensor swap sits at the low end. Tracing an intermittent short to voltage takes diagnostic time, and any repair on a heavily rusted exhaust system can run longer than the book time suggests.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0164 for my exact vehicle →
How to fix P0164
Easy — basic tools, most owners can do this
- Compare sensor 3 with bank 2 sensor 2
A genuinely rich exhaust would show up on the sensor ahead of it too. If bank 2 sensor 2 reads normally while sensor 3 sits pinned high, the mixture isn't the problem and the fault is in this sensor or its wiring; if both read high, look at the engine first.
- Check for rich codes and bank 2 trims anyway
Scan for P0175 and P0172 and look at fuel trims for both banks. Strongly negative trims on bank 2 alone hint at a leaking injector on that side; a rich condition is the priority repair, because it overheats converters while this sensor merely reports it.
- Open the connector and look for water bridging the pins
Far back under the car, this connector takes a steady bath of road spray. Unplug it and look for moisture, salt crust, or green corrosion linking the heater power terminal to the signal terminal; clean and dry it, add dielectric grease, and see whether the reading drops back to normal.
- Measure the unplugged signal wire for voltage
With the sensor unplugged and the key on, put a meter on the harness-side signal terminal. A healthy wire shows nothing or a small fixed bias; a reading close to battery voltage says the signal line has found a power source along its run — trace it back looking for a spot where the heater and signal wires have chafed together.
- Replace the sensor if the harness is clean
A dry connector and a sound harness leave the sensor itself, which can short internally between its heater and signal elements. Fit the replacement with anti-seize, clip the lead away from the pipe, and confirm the reading settles to a steady mid-range value after a warm drive.
DIY or shop? Everything here is within reach of a careful DIYer with jack stands, a multimeter, and a scan tool — a wet or corroded connector in particular is a common, nearly free fix. The sensor is accessible from below, though rust can make removal a fight. Hand it off if bank 2 sensor 2 also reads high and fuel trims point to a rich engine, since that diagnosis moves into injectors and fuel pressure, or if the short is hiding in a section of harness you can't reach without dropping heat shields.
Tools for the DIY steps: Scan tool with live data · Digital multimeter · Electrical contact cleaner · Dielectric grease · O2 sensor socket · Jack stands
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0164.
Start a case with P0164 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 P0164?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0164: common questions
What makes an O2 sensor read high voltage constantly?
Either the exhaust really is rich all the time, the sensor element has failed or been fouled, or the signal wire is touching a voltage source. Since exhaust after two catalytic converters is rarely rich for long, the sensor and wiring are the usual suspects for P0164.
Is P0164 related to P0430?
They involve the same area of the exhaust. P0430 is catalyst efficiency low on bank 2, and the downstream sensors are how the computer measures that efficiency. A faulty sensor 3 can prevent that monitoring from working properly, so fixing P0164 keeps converter diagnostics honest.
Can I just unplug the sensor if the car runs fine?
No — an unplugged sensor sets its own code (a no-activity fault like P0166), the check-engine light stays on, and you will not pass an OBD emissions inspection. There is no way to opt out of a sensor the vehicle was built with.
Do I need a special tool to replace this sensor?
An oxygen-sensor socket — a deep socket with a slot for the wire — makes the job much easier, and penetrating oil helps with rusted threads. It is a manageable DIY job on many vehicles if the sensor is accessible and not seized.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0164 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 P0164 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.