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P0155 is the Bank 2 version of P0135 - a heater circuit fault, not a sensor signal fault. If both P0135 and P0155 appear simultaneously, a shared fuse for O2 sensor heaters is the most likely cause. Check the fuse box for an O2 HTR fuse before purchasing two sensors - a single blown fuse sets heater codes for all sensors on that circuit. See OEM O2 sensors on Amazon ↗
🗺️ Where Is the Problem?
Exhaust diagram - P0155 heater circuit fault in the upstream O2 sensor on Bank 2
These are statistical causes across ALL vehicles - your exact car may rank differently
For example, on a Honda 4-cyl the downstream O2 sensor causes P0155 64% of the time, but on a GM 5.3L V8 the catalytic converter is the cause 71% of the time. Get a probability ranking built specifically for your year, make, model, and mileage.
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🎯 Top Causes & Probability
60%
#1 - Most Likely
Heater Element Failure in Bank 2 S1 Sensor
The ceramic heater inside the O2 sensor has burned out after high-mileage thermal cycling. Resistance measurement of the heater pins definitively identifies this failure. Without heater function, the sensor relies only on exhaust heat - insufficient for cold starts.
🔩 Part
$30–$150
👨🔧 Labor
$50–$150
⚡ DIY Difficulty
Easy
25%
#2 - Check First
Wiring Fault or Blown Fuse
Many vehicles share a common heater fuse across all O2 sensors. A single blown fuse disables all sensor heaters simultaneously. If P0135, P0141, and P0155 all appear together, start with the fuse before purchasing sensors.
🔩 Part
$2–$40
👨🔧 Labor
$0–$80
⚡ DIY Difficulty
Easy
15%
#3 - Less Common
PCM/ECM Driver Failure
The PCM controls heater activation via a solid-state driver. A failed driver disables the heater circuit output for Bank 2. This cause is rare and should be the final step in diagnosis after excluding all wiring and sensor causes.
🔩 Part
$200–$1,200
👨🔧 Labor
$100–$300
⚡ DIY Difficulty
Hard
🚗 Most Affected Vehicles
🔧 Step-by-Step Diagnosis
- Check O2 Heater Fuse - Before touching any sensors, find the O2 sensor heater fuse in the under-hood fuse box (labeled O2 HTR, HO2S HTR, or similar). Test with a test light or multimeter. A blown fuse that keeps blowing indicates a wiring short to ground in the heater supply circuit.
- Test B2S1 Heater Element Resistance - Unplug the Bank 2 upstream sensor connector. Identify the two heater circuit pins using the wiring diagram. Measure resistance between them. A healthy heater reads 5–20 ohms. An open reading (OL) confirms the heater element is burned out.
📍 Find a Trusted Shop Near You
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Tips for Choosing a Shop
- Ask if they charge a diagnostic fee and whether it applies toward the repair
- Request a written estimate before approving any work
- Ask specifically about the part brand - OEM vs. aftermarket matters for this code
- Check Google reviews for recent mentions of the specific repair you need