P0155 medium Severity

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

Check engine light illuminated; potential for reduced fuel economy, rough idle especially during cold start; generally minimal immediate drivability issues once warmed up

Overview

Generic OBD‑II P0155 indicates a fault in the heater circuit for the oxygen sensor upstream on Bank 2 (Sensor 1), often due to heater element failure, wiring issues, blown fuse, or PCM faults

Common Symptoms

  • Check Engine Light (CEL) illuminated
  • Poor fuel economy
  • Rough idle on cold start
  • Possible failed emissions test
  • Elevated emissions

Most Common Causes

Faulty oxygen sensor heater element high

Internal heater failure is frequently reported as the root cause in multiple technical references

Open or shorted heater circuit wiring high

Wiring harness damage or connector corrosion disrupting heater circuit continuity

Blown fuse in heater circuit medium

Fuse providing power to the O2 heater circuit can open and trigger P0155

Faulty PCM/ECM controlling heater circuit low

PCM failure is rare but documented as possible; confirm after eliminating sensor and wiring faults

Poor electrical connection or corrosion medium

Corroded terminals/connectors can increase resistance and trigger the code

Diagnostic Steps

  1. Scan vehicle with OBD‑II scanner
    Expected: P0155 code present; verify no other related codes (e.g., P0135, P0161)
    Interpretation: Confirm accuracy of P0155 and identify any simultaneous codes for comprehensive diagnosis
  2. Perform visual inspection of Bank 2 Sensor 1 O2 sensor and wiring
    Expected: No frayed wires, corrosion, or disconnected connectors
    Interpretation: Visible damage indicates wiring fault needing repair
  3. Check fuse for O2 sensor heater circuit
    Expected: Fuse intact with continuity
    Interpretation: Blown fuse indicates open circuit; replace and retest
  4. Measure heater circuit resistance with multimeter
    Expected: Resistance within manufacturer specification (low ohms)
    Interpretation: High resistance or open circuit suggests heater element or wiring fault
  5. Test voltage supply at heater circuit connector during crank
    Expected: Approximate battery voltage present
    Interpretation: No voltage suggests power supply or PCM driver issue
  6. Replace O2 sensor if heater element or resistance out of spec
    Expected: Code clears and does not return after test drive
    Interpretation: Successful repair if P0155 does not return

Repair Solutions

Replace Bank 2 Sensor 1 oxygen sensor medium
Estimated Cost: $150 - $400

Most common fix when heater element internally fails

Repair or replace wiring harness/connectors medium
Estimated Cost: $50 - $300

Costs vary depending on extent of wiring damage

Replace blown heater circuit fuse easy
Estimated Cost: $5 - $20

Simple and low cost; must confirm underlying cause of fuse blow

PCM diagnosis and repair/update hard
Estimated Cost: $200 - $1200

Only after ruling out sensor and wiring issues; rare

Common Misdiagnoses

Avoid these common diagnostic mistakes:

  • Replacing catalytic converter instead of faulty O2 sensor
  • Replacing O2 sensor when wiring issue is the actual cause

Frequently Asked Questions

Can you explain the meaning of P0155?

When your OBD-II scanner reads P0155, it means: O2 Sensor Heater Circuit Malfunction (Bank 2, Sensor 1). This code is related to the vehicle's Emissions.

Should I stop driving if I have P0155?

You should treat P0155 as a medium issue. Check engine light illuminated; potential for reduced fuel economy, rough idle especially during cold start; generally minimal immediate drivability issues once warmed up

How do I know if I have code P0155?

You may experience the following: Check Engine Light (CEL) illuminated, Poor fuel economy, Rough idle on cold start.

Why is my car throwing a P0155 code?

Potential culprits include: Faulty oxygen sensor heater element, Open or shorted heater circuit wiring, Blown fuse in heater circuit. A proper diagnosis is recommended.

Estimated repair costs for different causes of P0155

Expect to pay around $20 if the issue is a Replace blown heater circuit fuse, but up to $1200 if the PCM diagnosis and repair/update needs replacement.

Is P0155 a generic or manufacturer-specific code?

The P0155 code is a generic powertrain code, meaning it applies to almost all makes and models, such as Honda, Toyota, VW, Ford, and Chevy.

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