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DTC code page

P0155: O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)

Quick answer: The upstream oxygen sensor heater on Bank 2 is not warming the sensor the way the ECU expects.

Drivers also search this fault as bank 2 sensor 1 heater circuit, upstream O2 heater bank 2, oxygen sensor heater malfunction bank 2 sensor 1.

Severity: medium Family: powertrain Related paths: 9
Meaning

What P0155 usually means

P0155 is the Bank 2 counterpart to P0135. It points to the heater circuit for the upstream oxygen sensor on Bank 2 Sensor 1. The sensor may still read exhaust oxygen eventually, but if the heater is slow or dead the engine can stay in open loop longer, readiness can suffer, and Bank 2 fuel-control diagnostics become less reliable during warm-up.

Fast triage

Start here before chasing parts

  • Scan first: save freeze-frame and pending codes before clearing anything.
  • Confirm the complaint: compare the stored code with current drivability symptoms.
  • Use context: trims, live data, and related codes usually narrow the fault faster than guesswork.
  • Work simplest to hardest: leaks, connectors, maintenance items, and known patterns before expensive components.
Initial checks

What to check first

  • Verify which side of the engine is Bank 2 before testing or ordering parts.
  • Inspect the Bank 2 upstream sensor connector and nearby harness for heat damage and corrosion.
  • Check shared heater power supply or fuse first because one feed issue can affect more than one O2 heater code.
Driving risk

Can you keep driving?

P0155 usually is not a stop-driving code, but it can delay closed-loop operation and make Bank 2 mixture diagnosis less clean until it is fixed.

Moderate urgency: This code often allows short-term driving, but the right fix usually comes faster when you diagnose it early instead of waiting for more codes.
Likely causes

Common causes behind this code

  • Failed heater element inside the Bank 2 upstream oxygen sensor
  • Open or short in the Bank 2 heater circuit wiring
  • Shared fuse or power-supply problem feeding the oxygen-sensor heaters
  • Connector corrosion, poor terminal fit, or heat damage near the exhaust
  • Ground-side resistance that prevents the heater from operating correctly

Cause phrases often tied to this code: failed oxygen sensor heater, blown fuse, heater wiring fault, connector damage, high resistance.

Diagnostic order

Suggested workflow

  1. Confirm sensor location and inspect the Bank 2 Sensor 1 harness near the exhaust manifold.
  2. Check for battery voltage and a working ground path at the heater circuit.
  3. Measure heater resistance only after wiring, fuse, and connector basics are checked.
  4. If other Bank 2 fuel-trim codes are present, separate heater warm-up delay from a true mixture fault.
  5. After repair, confirm the engine enters closed loop normally and Bank 2 warm-up behavior looks normal.
Avoid guesswork

Common mistakes

  • Ordering the wrong sensor because Bank 1 and Bank 2 locations were never confirmed.
  • Replacing the sensor without checking the shared heater fuse or feed circuit.
  • Mixing P0155 up with a Bank 2 lean or rich fault and missing the heater-only problem.
Repair path

Practical fix guidance

  • Repair fuse, power, ground, or connector problems before replacing the sensor if the heater itself is not proven open.
  • Replace the correct Bank 2 upstream sensor when the heater element is confirmed faulty.
  • After the fix, verify Bank 2 trim and readiness recover normally instead of assuming the light staying off is enough.
Vehicle context

Affected brands in this MVP

Brand hubs help broaden internal linking now and can evolve into make-specific diagnostic notes later.

Aliases and common searches

English phrases tied to P0155

Useful when the driver knows the wording but not the exact DTC yet.

  • bank 2 sensor 1 heater circuit
  • upstream O2 heater bank 2
  • oxygen sensor heater malfunction bank 2 sensor 1
Related search intent

Queries this page can answer naturally

  • P0155 code meaning
  • what does P0155 mean
  • O2 heater circuit bank 2 sensor 1
  • Bank 2 upstream O2 heater fault
FAQ

Quick questions about P0155

Is P0155 basically the Bank 2 version of P0135?

Yes. Both are upstream oxygen-sensor heater faults; P0135 is Bank 1 Sensor 1 and P0155 is Bank 2 Sensor 1.

Can a fuse cause P0155?

Yes. Shared heater power-supply issues are common enough that the fuse and feed should be checked early.

Will P0155 by itself make the engine run badly?

Often only mildly, but cold-start fuel control and readiness can be affected until the heater works again.