BMW P0155: O2 Sensor Heater Circuit Malfunction Bank 2 Sensor 1 — Diagnosis and Repair

P0155 means O2 Sensor Heater Circuit Malfunction Bank 2 Sensor 1. The DME records it when heater current or warm-up behavior is implausible; diagnosis must separate an electrical signal fault from a real system fault. Use OBDThink to preserve the recording module and freeze frame for P0155, then test heater circuit of the pre-catalyst lambda sensor on bank 2 without guessing or swapping parts. What Does P0155 Mean? This standardized powertrain DTC concerns heater circuit of the pre-catalyst lambda sensor on bank 2. On BMW vehicles the exact test plan and component layout vary by engine, chassis and DME software, so verify the VIN in BMW service information. The decisive clue is not the code alone: heater current or warm-up behavior is implausible. Compare commanded behavior with the measured signal before condemning a component. Code: P0155 Definition: O2 Sensor Heater Circuit Malfunction Bank 2 Sensor 1 Module: DME (gasoline) or DDE where applicable Key evidence: heater current or warm-up behavior is implausible Typical causes: open bank-2 heater, supply fuse fault, connector resistance, heat-damaged loom, or DME driver fault Severity: diagnose promptly Note: confirm engine and wiring variant by VIN First preserve the freeze frame. If heater current or warm-up behavior is implausible, inspect heater circuit of the pre-catalyst lambda sensor on bank 2 and its supporting system in the same operating condition. Symptoms • O2 Sensor Heater Circuit Malfunction Bank 2 Sensor 1 commonly appears with delayed closed-loop control, bank-specific fuel-trim drift, fuel smell and catalyst stress. • The freeze frame may show the fault while heater current or warm-up behavior is implausible, which is more useful than the warning lamp alone. • Target and actual values separate a persistent defect from an intermittent connector or harness interruption. • A companion fault from the same module may identify whether heater circuit of the pre-catalyst lambda sensor on bank 2 is the cause or a consequence. Possible Causes Start with accessible circuit and connection checks, then prove the sensor or actuator, and leave expensive mechanical work until last. • Low cost: inspect the connector, terminal tension, contamination and the harness around heater circuit of the pre-catalyst lambda sensor on bank 2. • Low cost: check hoses, ducts, grounds, fuses and supply paths that directly affect heater circuit of the pre-catalyst lambda sensor on bank 2. • Medium cost: test the named sensor or actuator dynamically; the defining evidence is that heater current or warm-up behavior is implausible. • Medium cost: correct the system condition rather than masking it; likely branches include open bank-2 heater, supply fuse fault, connector resistance, heat-damaged loom, or DME driver fault. • High cost: only after circuit and mechanical evidence, consider control-unit repair or major mechanical work using VIN-specific BMW service data. Diagnosis Steps with OBDThink OBDThink is an independent BMW coding and diagnostic mobile app and is not affiliated with BMW AG. Available live data and freeze frame detail depend on the vehicle, adapter and module. • 1. Scan every control unit with OBDThink; save P0155, the recording DME, status, frequency and freeze frame before clearing anything. • 2. Reproduce the recorded operating condition safely and graph target versus actual values. Graph the affected pre-catalyst lambda signal and heater status against the opposite bank; inspect the exhaust and hot-zone harness. • 3. With ignition safely isolated where required, inspect and electrically test heater circuit of the pre-catalyst lambda sensor on bank 2; load-test power and ground rather than relying on continuity alone. • 4. Separate circuit from mechanism: manipulate the harness while monitoring data, then perform the relevant smoke, vacuum, pressure, airflow or waveform test. • 5. Confirm the repair by clearing the code, completing a cold start and controlled drive cycle, and rescanning all related modules. IF heater current or warm-up behavior is implausible AND wiring/load test fails -> repair the circuit ELSE IF command is correct but mechanism does not respond -> test heater circuit of the pre-catalyst lambda sensor on bank 2 ELSE compare companion faults and BMW VIN-specific test plan THEN clear, drive, and rescan The fastest distinction is to watch the relevant command and actual value while testing heater circuit of the pre-catalyst lambda sensor on bank 2; a fixed signal and a responding mechanism point in different directions. Repair • Low cost: clean and secure the correct connector, repair chafed wiring, restore a fuse/ground, or replace a split hose only when testing proves it. • Medium cost: replace the confirmed sensor, valve, relay or solenoid and perform any BMW service-data adaptation that genuinely applies. • Medium cost: repair the verified airflow, vacuum, exhaust or fuel-delivery defect that caused the implausible reading. • High cost: repair the pump, turbocharger, timing hardware, cylinder-head passage or DME only after VIN-specific testing rules out cheaper causes. After repair, verify that heater current or warm-up behavior is implausible no longer occurs, readiness can complete, and P0155 does not return as pending or confirmed. Can You Drive with P0155? A short trip is usually possible, but prolonged rich running can overheat and damage the catalyst. Treat P0155 as measured evidence, not a parts order. A saved freeze frame, a target/actual comparison and a load-tested circuit usually reveal the least expensive correct repair.