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DTC codes / P01xx · Fuel and air metering / P0164

P0164O2 Sensor Circuit High Voltage (Bank 2 Sensor 3)

P0164 indicates that the powertrain control module (PCM) has detected a sustained high voltage signal from the downstream oxygen sensor on bank 2, which is the side of the engine that does not contain cylinder number one. The sensor is reporting a voltage above the normal range, typically above 1.1 volts, which the PCM interprets as an excessively rich exhaust condition or a circuit fault.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaFuel and air metering

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms
  • A slight decrease in fuel economy due to the PCM commanding a leaner mixture based on the false rich signal
  • Possible rough idle or hesitation if the false signal is severe enough to disrupt fuel trim
  • In rare cases, a sulfur or rotten egg smell from the exhaust if the engine is actually running rich
  • Failed emissions test due to the stored trouble code and potential increase in tailpipe emissions

Common causes, most likely first

  1. A failed downstream oxygen sensor that is stuck at a high voltage output
  2. A short to voltage in the sensor signal wire between the sensor and the PCM
  3. A short to voltage in the sensor heater circuit that is back-feeding the signal circuit
  4. Contaminated sensor element from excessive oil ash, coolant, or silicone poisoning
  5. A faulty PCM driver for the oxygen sensor circuit, though this is less common
  6. Exhaust leaks upstream of the sensor allowing outside air to be drawn in and misread
  7. A rich-running condition that is actually present, such as a leaking fuel injector or high fuel pressure

How to diagnose and fix it

  1. Use a scan tool to verify the code and check live data for the bank 2 sensor 3 voltage to confirm it is stuck high
  2. Inspect the sensor wiring and connector for damage, corrosion, or signs of voltage back-feeding from the heater circuit
  3. Check for exhaust leaks between the engine and the sensor that could cause a false lean reading and subsequent rich command
  4. Test the sensor signal circuit for a short to voltage using a digital multimeter with the key on and sensor disconnected
  5. If the circuit tests normal, remove the sensor and inspect for contamination or physical damage, replacing if necessary
  6. After repair, clear the codes and perform a drive cycle to verify the sensor switches normally and the code does not return
  7. If the code persists after sensor replacement, diagnose the PCM and its connectors for internal faults

Why a high voltage reading is not always a bad sensor

  • A short to voltage in the sensor heater circuit can force the signal wire high, so always check for voltage on the signal wire with the sensor disconnected before condemning the sensor.
  • Exhaust leaks upstream of the sensor can cause a false lean condition that the PCM tries to correct by adding fuel, which can drive the downstream sensor voltage high and set this code.
  • A stuck-high downstream sensor can be caused by a rich-running engine from a leaking injector or high fuel pressure, so fuel trim data must be reviewed before replacing parts.
  • Some vehicles use a wide-band oxygen sensor for the downstream position, and a high voltage reading on these sensors may indicate a different failure mode than a traditional narrow-band sensor.
  • The PCM may set P0164 as a result of a faulty ground connection for the sensor, which can cause the reference voltage to appear high on the signal circuit.

Can I keep driving with P0164?

The vehicle is generally safe to drive with this code because the PCM will default to a safe fuel strategy, but prolonged driving with a false rich signal can lead to increased fuel consumption and emissions. Avoid heavy acceleration and towing until the fault is repaired, and address the issue promptly to prevent potential damage to the catalytic converter.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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