P0155 - O2 Sensor Heater Circuit Malfunction (Bank 2, Sensor 1)
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
P0155 indicates that the powertrain control module (PCM) has detected a malfunction in the heater circuit of the oxygen (O2) sensor located in Bank 2, Sensor 1 (upstream of the catalytic converter). Oxygen sensors must reach an operating temperature of approximately 600°F (315°C) to provide accurate voltage signals. The PCM monitors the heater circuit via current draw or by timing how long it takes for the sensor to enter closed-loop operation. If the resistance is out of spec or the circuit is open, this DTC is triggered.
Possible Causes
Internal heater element failure in the O2 sensor (open circuit)
Damaged wiring or corroded connectors leading to the sensor
Blown fuse for the oxygen sensor heater circuit
Faulty engine control module (PCM/ECU) ground driver
Symptoms
Recommended Solution
- Visual Inspection: Check the connector at Bank 2 Sensor 1 for corrosion, terminal tension, or heat damage to the wiring harness.
- Fuse Check: Inspect the O2 heater fuse in the power distribution center.
- Resistance Test: Disconnect the sensor and measure resistance across the heater pins (typically the two wires of the same color, often white). Specs are usually 2-20 Ohms. Infinite resistance (OL) indicates a failed sensor.
- Voltage Test: Verify 12V power at the harness connector with the key on.
- Component Replacement: If the heater resistance is out of spec, replace the oxygen sensor.
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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