OBD codes / P0164
P0164
ModerateO2 Sensor Circuit High Voltage (Bank 2, Sensor 3)
No urgency for the engine itself — drive normally and schedule the repair. If you also notice a fuel smell, black exhaust, or a rich code like P0175, treat the mixture problem as the priority, because sustained rich running is what actually damages catalytic converters.
What this code 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.
Symptoms you might notice
- 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
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 →
Frequently asked
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.
Seeing P0164 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0164 for my vehicleRelated trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0164 from your phone — see our honest guide to the best OBD2 Bluetooth adapters.
Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.