P0167 O2 Sensor Heater Circuit Malfunction Bank 2 Sensor 3
The error code P0167 indicates a malfunction in the heater circuit of the oxygen (O2) sensor located on Bank 2, Sensor 3 (S3). This generic powertrain code applies to most vehicles produced since 1996, although specific diagnostic procedures may vary slightly by manufacturer and model.
Function of the O2 Sensor Heater Circuit
Modern oxygen sensors are equipped with an integrated heating element. Its role is crucial: to quickly heat the sensor so it can reach its optimal operating temperature (usually around 600°F or 315°C) as soon as the engine starts. A hot sensor allows the engine management system to enter “closed loop” mode more quickly, a state where it continuously adjusts the air-fuel mixture based on the O2 sensor readings. This significantly improves combustion efficiency, reduces pollutant emissions, and ensures stable idling.
Symptoms of Code P0167
It is common for the P0167 code to illuminate without any drastic symptoms immediately noticeable to the driver. However, the following signs may appear:
- Illumination of the Malfunction Indicator Lamp (MIL) on the dashboard.
- Possible increase in pollutant emissions (failure in emissions testing).
- Slightly increased fuel consumption.
- Slightly rough or lean idle.
- In some cases, the engine may enter a degraded mode (“limp mode”).
Potential Causes of the Malfunction
Several elements can be the cause of the P0167 code:
- Faulty O2 Sensor: The internal heating element is burnt out or short-circuited.
- Wiring Problems: Cut, frayed, melted, or corroded wires leading to the sensor.
- Damaged Connector: Poor contact, oxidation, or loose pins at the sensor or PCM connector.
- Blown Fuse: The fuse protecting the sensor heater circuit has blown.
- Ground Problem: A poor ground for the heater circuit.
- PCM Failure: Rare, but possible, an internal issue with the control module.
Diagnosis and Solutions for Resolving Code P0167
A methodical approach is essential to diagnose and repair the root cause.
Step 1: Visual Inspection
Start with a thorough inspection. Locate the O2 sensor on Bank 2, Sensor 3 (usually after the catalytic converter). Examine the sensor itself, the wiring harness, and its connector for any obvious signs of physical damage, corrosion, or burns caused by the exhaust system. Also, check the condition of the relevant fuses in the fuse box.
Step 2: Checking Power and Ground
Required Equipment: Digital Multimeter (voltmeter/ohmmeter).
- With the ignition on (engine off – KOEO), disconnect the O2 sensor connector.
- Using the voltmeter, check for the presence of +12V at the heater circuit power supply pin (refer to the repair manual to identify the pins). Connect the multimeter’s ground to the battery.
- If battery voltage (≈12V) is present: The problem is likely not with the power supply. Next, check the continuity of the heater circuit ground (with the ignition off). If the ground is good, the O2 sensor itself is very likely faulty and needs to be replaced.
- If battery voltage is absent: Check and replace the relevant fuse if necessary. If the fuse is blown, look for a short to ground on the power supply wire before replacing the fuse. If the fuse is intact, look for a break (open) in the power supply wire between the PCM/relay and the connector.
Step 3: Checking Sensor Resistance
With the ignition off and the sensor disconnected, measure the resistance of the heating element between the two corresponding pins on the sensor (off the vehicle). The value varies by model (often between 2 and 10 Ω). An infinite resistance (open circuit) or zero resistance (short circuit) confirms sensor failure.
Conclusion and Call to Action
Although sometimes asymptomatic, the P0167 code should not be ignored. An O2 sensor that does not heat properly prevents the engine management system from operating optimally, which can lead to increased fuel consumption and premature wear of the catalytic converter.
If the diagnostic steps described above seem complex, it is highly recommended to consult a professional mechanic. Equipped with an advanced automotive scanner and precise wiring diagrams, they can identify and resolve the problem efficiently, ensuring optimal performance and compliance with pollution standards for your vehicle.