Comprehensive diagnostic guide for P0167

O2 Sensor Heater Circuit Low (Bank 2 Sensor 3)

What This Code Means

• Standard definition (OBD-II): P0167 = O2 Sensor Heater Circuit Low (Bank 2 Sensor 3). This is a powertrain-related DTC that indicates the heater element for the Bank 2 Sensor 3 oxygen sensor is not reaching the expected heating condition, causing delayed sensor response and inaccurate air-fuel readings.
• Open Source code reference: The provided definition in Portuguese reads i.e., O2 sensor heater circuit malfunction for sensor 3 on bank 2. This aligns with the general concept of a heater circuit fault affecting that specific sensor.
• Relevance: DTCs in OBD-II are monitored by the vehicle's powertrain control module (PCM/ECU). The network and sensors are designed to monitor O2 sensor heater operation as part of the emissions-related readiness checks (Emissions Testing context).

What This Code Means

• P0167 indicates the heater circuit for Bank 2 Sensor 3 is not operating within expected parameters. Without proper heating, the O2 sensor cannot reach its stable operating temperature quickly or reliably, which can lead to delayed sensor response and suboptimal fuel control.
• This can affect emissions readiness and may contribute to rich/lean conditions if the sensor's readings are delayed or inaccurate.

Symptoms

• Check Engine/ MIL illumination with P0167 stored in ECU.
• Longer catalyst warm-up times or poor monitoring of downstream O2 sensors.
• Potential for degraded fuel economy or driveability symptoms if the sensor's readings are delayed during cold starts or transient operation.
• In some cases, the vehicle runs normally but the MIL remains on until the fault is repaired and codes are cleared.
  Note: Symptoms can be vehicle-specific and may be influenced by other O2 sensor codes or engine/ exhaust conditions.

Probable Causes

• Faulty Bank 2 Sensor 3 O2 heater element or internal sensor failure: 45-60%
• Damaged or corroded wiring, connectors, or harness to Bank 2 Sensor 3 heater circuit: 20-35%
• Open or high-resistance circuit due to a blown fuse, relay, or power supply issue to the heater: 3-10%
• Grounding issues or shorts to ground in the heater circuit: 3-10%
• PCM/ECU control or software fault affecting the heater output (less common): 1-5%

Notes:

• The above percentages are approximate field estimates; exact causes vary by vehicle and design (especially the exact sensor location and wiring harness routing for Bank 2 Sensor 3). A thorough diagnostic should verify wiring, power, and sensor condition before replacement.

Diagnostic Approach

1) Verify the fault and gather data

• Use a scan tool to confirm P0167 is present and check for related codes (e.g., other O2 sensor codes, heater circuit-related codes for other sensors, or misfire/lean/rich codes). Record freeze-frame data and vehicle conditions at the time of the fault.
• Confirm the sensor bank/position: Bank 2 Sensor 3 is typically a downstream oxygen sensor on bank 2 (the exact location can vary by engine family). If your vehicle does not have a Bank 2 Sensor 3, or uses a different sensor indexing, verify with the factory service information.

2) Visual inspection

• Inspect the Bank 2 Sensor 3 harness, connectors, and the immediate wiring for visible damage, abrasion, pin corrosion, or moisture intrusion.
• Check for melted insulation, exposed conductors, or signs of heat damage near the sensor and connector.
• Inspect fuses/relays related to the O2 heater circuit if accessible (vehicle-specific fuse/relay layout).

3) Electrical checks (power/ground and heater circuit)

• With engine off, inspect the heater circuit wires from the battery/ECU/PCM supply pathway to the sensor heater. Look for signs of wire damage or loose grounds.
• With key on (engine off) or engine running as appropriate for the vehicle, measure heater circuit voltage at the sensor connector reference (as specified in the service manual). The heater circuit should show supply voltage when commanded/on.
• Measure resistance of the O2 heater element (at the sensor connector). Compare measured resistance to the OEM/service spec. A circuit that is open or shows abnormally high resistance indicates a faulty sensor or wiring issue.
• If the heater is not energizing, backprobe to verify if the ECU/PCM is supplying power to the heater, or if the fault is upstream (fuse/relay/trace).

4) Functional test with live data

• Use a scan tool to observe the Bank 2 Sensor 3 heater status (ON/OFF) and the sensor's voltage/current reading while the engine is at operating temperature.
• For a healthy heater circuit, the heater should energize (ON) and allow the sensor to reach operating temperature relatively quickly after startup. If the heater never turns ON or remains OFF, suspect heater element, wiring, or ECU control logic.

5) Sensor health determination

• If electrical checks show good power supply and ground, but the heater resistance is out of spec or the heater never energizes, replace Bank 2 Sensor 3.
• If wiring or harness damage is found, repair or replace the affected wiring/connector. If damage is localized to the sensor end connector, replacing the Sensor 3 assembly with a new harness is often practical.
• If the ECU/PCM is suspected (e.g., no heater command despite good wiring), consult service information for possible software updates or reprogramming; in rare cases this may require OEM-level diagnostics.

6) Post-repair verification

• Clear P0167 and any related codes.
• Start the engine and monitor live data to confirm Bank 2 Sensor 3 heater is energized and the sensor heats to normal operating temperature. Ensure the sensor begins to report accurate readings as the catalyst reaches light-off temperature.
• If applicable, perform an emissions readiness check and verify that the downstream sensor data stabilizes as expected after multiple drive cycles.

Location considerations (general guidance)

• Bank 2 Sensor 3 is commonly a downstream O2 sensor on bank 2 (the exact positioning varies by engine design). Some vehicles use downstream sensors labeled 3 or 4; others may not have a Sensor 3 at all. Always confirm with the factory service information for your specific engine code and model year.

Repair Options

• Replace Bank 2 Sensor 3 oxygen sensor (including new connector seals if required) when the heater circuit itself is determined to be faulty or the sensor is physically damaged.
• Repair or replace damaged wiring/connector harness to the Bank 2 Sensor 3 heater circuit; reseal and re-seat connectors, ensuring proper pin alignment and protection from moisture.
• Replace faulty fuse/relay or repair power supply to the heater circuit if the fault is upstream.
• Update or re-flash ECU/PCM if a software/firmware issue is suspected and supported by the manufacturer.

Documentation

• Explain that P0167 is an O2 sensor heater circuit fault for Bank 2 Sensor 3, which can affect how quickly and accurately the oxygen sensor provides data to the ECU, with potential impacts on emissions and fuel economy.
• Outline the diagnostic steps taken, the parts likely to be involved (sensor vs wiring vs power supply), and the expected repair scope (sensor replacement, wiring repair, or ECU-related service if necessary).
• Discuss potential cost ranges and timelines, noting that exact costs vary by vehicle and parts availability.

Safety Considerations

• Use appropriate PPE when handling exhaust and sensors; exhaust components can be hot after engine operation.
• Disconnect battery before servicing electrical connectors in the O2 heater circuit to avoid short circuits or electric shock.
• Follow OEM service information for torque specs, sensor replacement procedures, and any special cautions (e.g., sensor anti-seize requirements, wiring harness routing, and contamination prevention).
• After any repair, verify no other related DTCs reappear and confirm the emissions readiness monitors pass during road testing or drive cycle.

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II
• Open-Source OBD2 Data: N/A (MIT)

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

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