P0155 code: O2 Sensor Heater Circuit (Bank 2, Sensor 1)
P0155 means o2 Sensor Heater Circuit (Bank 2, Sensor 1). The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0155 means
P0155 is the Bank 2 twin of P0135: the heater circuit in the upstream oxygen sensor on the other cylinder bank (the side with cylinder 2) isn't drawing the right current. Oxygen sensors have a built-in heater so they reach operating temperature quickly after a cold start. Almost always the sensor's own heater element has failed, so replacing the sensor is the usual fix — but a blown fuse or a wiring fault can cause it too. It only applies to V6/V8/V-style engines with two banks.
P0155 symptoms
- Check-engine light, often with no drivability change
- Slightly worse fuel economy, especially on short trips
- Possible failed emissions test
What it costs to fix P0155
Typical range: $150–$450 · about ~0.3–1 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Upstream oxygen (O2) sensor | $50–$250 | ~0.3–1 hrs |
| Fuse | $1–$10 | ~0.1–0.3 hrs |
| Wiring / connector repair | $10–$120 | ~0.5–1.5 hrs |
The sensor is the usual fix, a low-hundreds job. Check the cheap things first — a blown fuse or chafed wire occasionally causes it for almost nothing. OEM sensors on some makes cost more than aftermarket.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0155 for my exact vehicle →
How to fix P0155
Moderate — doable at home with common tools and patience
- Identify which sensor is Bank 2 Sensor 1
Bank 2 is the cylinder bank containing cylinder 2 — on many transverse V6s that's the bank at the firewall, but it varies by make, so confirm for your engine before buying or unbolting anything. Replacing the wrong sensor is the most common mistake with bank 2 codes.
- Rule out the shared fuse
Test the O2 heater fuse; if it's blown you'd usually see heater codes from multiple sensors at once. One lone P0155 with a good fuse points squarely at that sensor or its local wiring.
- Inspect the wiring at the bank 2 manifold
Check the sensor's pigtail for heat damage where it passes near the bank 2 exhaust manifold and confirm the connector is latched and corrosion-free. Rear-bank harnesses are often routed tightly and can sag onto hot metal over the years.
- Test the heater element with a multimeter
Unplug the sensor and measure across its heater pins: continuity in the single-digit-to-low-teens ohm range means the heater is alive, while an open reading condemns the sensor. Also verify the harness side has power and ground with the engine running.
- Replace the Bank 2 Sensor 1 sensor
Swap in a new upstream sensor on bank 2, using penetrating oil, an O2 socket, and anti-seize on the threads. On engines where this sensor faces the firewall, expect to work by feel or from underneath.
DIY or shop? Electrically this is the same friendly diagnosis as any heater code — fuse, wiring, and a two-pin resistance check. What tips it toward a shop on some vehicles is pure access: the bank 2 upstream sensor is frequently the hardest-to-reach sensor on the engine, jammed between the rear manifold and the firewall. If you can see and reach it, do it yourself; if you can only barely touch it, a shop with a lift and swivel sockets will save your knuckles and probably the sensor's wiring too.
Tools for the DIY steps: Multimeter · O2 sensor socket and swivel extensions · Penetrating oil · Anti-seize compound · Flashlight or inspection mirror · Jack and jack stands (if accessing from below)
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0155.
Start a case with P0155 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P0155?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0155: common questions
Can I drive with P0155?
The code doesn't answer that on its own; what it does tell you is that this is a low-urgency fault affecting emissions and warm-up fuel economy. Fix it before an emissions test.
Is P0155 the same as P0135?
Same fault, opposite bank: P0135 is the upstream sensor's heater on Bank 1, P0155 is the upstream sensor's heater on Bank 2 (the cylinder-2 side). Diagnosis and repair are identical.
Does P0155 mean a new O2 sensor?
Usually — the failed heater is inside the sensor, so the sensor gets replaced. Check the fuse and wiring first in case one of those cheap items is the cause.
How much does it cost to fix P0155?
Typically a low-hundreds repair if it's the sensor. Less if it's a fuse or wiring fix. A seized or hard-to-reach sensor adds labor.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0155 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P0155 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.