P0155 Code: O2 Heater Circuit (Bank 2 Sensor 1)
The P0155 trouble code means the PCM detected a fault in the oxygen (O2) sensor heater circuit for Bank 2 Sensor 1 (the upstream/front sensor on Bank 2). The heater helps the sensor reach operating temperature quickly so fuel control can stabilize and emissions stay low.
What Does P0155 Mean?
Heated oxygen sensors use an internal heater so the sensor reaches operating temperature quickly after startup. If the PCM detects an open circuit, short, or abnormal heater current/response for the Bank 2 upstream sensor, it sets P0155.
Where Is Bank 2 Sensor 1 Located?
Bank 2 Sensor 1 (B2S1) is the upstream/front oxygen sensor on Bank 2. It is typically installed in the exhaust manifold or the exhaust pipe near the manifold, before the catalytic converter.
Symptoms of P0155
- Check Engine Light (CEL)
- Longer time to enter closed loop after cold start
- Reduced fuel economy (sometimes)
- Roughness during warm-up (sometimes)
- Increased emissions (common)
Common Causes of P0155
Heater circuit / sensor issues
- Failed heater element inside the O2 sensor
- Damaged wiring near hot exhaust components
- Loose connector, corrosion, bent pins
Power/ground problems
- Blown fuse feeding the O2 heater circuit
- Faulty relay (on some vehicles)
- Poor ground path for the heater circuit
Less common
- PCM/ECM driver issue (rare)
- Aftermarket wiring changes creating high resistance
How Serious Is P0155?
P0155 is usually not an immediate breakdown code. Many vehicles drive normally, but warm-up performance can be worse, fuel economy may drop, and emissions can increase. Heater faults can also interfere with readiness completion on some vehicles.
How to Diagnose P0155
- Confirm the code and check for related heater or catalyst codes.
- Inspect the harness for melting, rubbing, or broken wires near the exhaust.
- Inspect the connector for corrosion, water intrusion, or loose pins.
- Check the heater fuse (and relay if equipped) used for O2 sensors.
- Verify heater circuit integrity (open/short conditions are common triggers for heater codes).
How to Fix P0155 (Most Effective Repairs)
| Repair | Most likely when |
|---|---|
| Replace Bank 2 Sensor 1 O2 sensor | Heater element failure or persistent heater fault with wiring intact |
| Repair wiring/connector | Harness damage or corrosion found |
| Replace fuse/repair power supply | O2 heater fuse is blown or power feed fault is present |
| Repair ground connection | Ground fault causing heater circuit malfunction |
P0155 Repair Cost Estimates
| Repair | Estimated Cost |
|---|---|
| O2 sensor replacement (B2S1) | $120 – $350 |
| Wiring/connector repair | $50 – $250 |
| Fuse/relay repair | $10 – $150 |
External Resources
Authoritative references that support emissions and diagnostics topics.
FAQs
Is P0155 upstream or downstream?
P0155 is Bank 2 Sensor 1, which is the upstream/front oxygen sensor on Bank 2.
Will P0155 cause drivability problems?
Often no, but warm-up performance may be rougher and fuel economy can drop. Emissions typically increase until the issue is repaired.
Can P0155 contribute to P0430?
It can contribute to fuel control and catalyst monitoring, but P0430 typically requires its own diagnosis.